The WASA-FRS project at GSI and its perspective
T.R. Saito, P. Achenbach, H. Alibrahim Alfaki, F. Amjad, M. Armstrong, K.-H. Behr , J. Benlliure, Z. Brencic, T. Dickel, V. Drozd, S. Dubey, H. Ekawa, S. Escrig, M. Feijoo-Fontan, H. Fujioka, Y. Gao, H. Geissel, F. Goldenbaum, A. Grana Gonzalez, E. Haettner, M.N. Harakeh, Y. He, H. Heggen, C. Hornung, N. Hubbard, K. Itahashi, M. Iwasaki, N. Kalantar-Nayestanaki, A. Kasagi, M. Kavatsyuk, E. Kazantseva, A. Khreptak, B. Kindler, R. Knoebel, H. Kollmus, D. Kostyleva, S. Kraft-Bermuth, N. Kurz, E. Liu, B. Lommel, V. Metag, S. Minami, D.J. Morrissey, P. Moskal, I. Mukha, A. Muneem, M. Nakagawa, K. Nakazawa, C. Nociforo, H.J. Ong, S. Pietri, J. Pochodzalla, S. Purushothaman, C. Rappold, E. Rocco, J.L. Rodríguez-Sanchez, P. Roy, R. Ruber, S. Schadmand, C. Scheidenberger, P. Schwarz, R. Sekiya, V. Serdyuk, M. Skurzok, B. Streicher, K. Suzuki, B. Szczepanczyk, Y.K. Tanaka, X. Tang, N. Tortorelli, M. Vencelj, H. Wang, T. Weber, H. Weick, M. Will, K. Wimmer, A. Yamamoto, A. Yanai, J. Yoshida, J. Zh
abstract
A novel technique to study bound states of exotic hadrons in subatomic nuclei, such as hypernuclei and mesic nuclei, has been developed by employing the Fragment Separator FRS and the WASA central detector at GSI. Two experiments, S447 for studying light hypernuclei, especially hypertriton and a ????nn bound state, and S490 for searching for ????? mesic-nuclei, were recently performed. Data analyses are currently in progress, and light charged particles such as protons and ????? are clearly observed and identified in the both experiments. For S447, light nuclear fragments that can also be residual nuclei from decays of hypernuclei of interests have been analysed by the FRS, and a momentum resolution, ?????????????, of 5 × 10?4 has been achieved. Further data analyses are to be completed. The WASA-FRS project will be continued and extended with the FRS at FAIR Phase 0, and upgrading of the WASA magnet and detectors is currently in progress. Furthermore, construction
of a larger detector system with the Super-FRS at FAIR Phase 1 is also under consideration.
Search for eta-mesic nuclei: A review of experimental and theoretical advances
A. Khreptak, M. Skurzok, P. Moskal
abstract
In the mid-1980s, theoreticians predicted possible exotic states of an eta meson and a nucleus bound by the strong interaction, so-called mesic nucleus. This led to extensive experimental efforts aimed at discovering such unstable states as well as understanding the underlying interactions via eta meson production reactions. As experiments yielded new data, more and more sophisticated theoretical models were developed to understand the fundamental eta-nucleon and eta-nucleus interactions. After more than 35 years of research in this field, several signals have been identified as possible indications of hypothetical eta-mesic nuclei, but there is still no general agreement or clear confirmation of their existence. In the paper, we review the study of the eta-mesic nuclei with an emphasis on recent research activities.
The eta- and eta'-nucleus interactions and the search for eta, eta'- mesic states
S. D. Bass, V. Metag, P. Moskal
abstract
The isoscalar eta and eta? mesons are special in QCD, being linked both to chiral symmetry and to non-perturbative glue associated with the axial anomaly. The properties of these mesons in medium are sensitive to how these dynamics work in the nuclear environment. In contrast to pionic and kaonic atoms which are mainly bound by the Coulomb interaction with some corrections due to the strong force (Coulomb assisted binding), the eta and eta' as neutral mesons can only be bound by the strong interaction. Is this interaction strong enough? This topic has inspired a vigorous program of experiments, conducted in close contact with theory, One has to determine the complex eta, eta'-nucleus potential. Does the real part V provide a sufficiently deep potential? Is the imaginary part W small enough to allow for narrow states that can more easily be detected experimentally, i.e. |W|<<|V|? The eta' effective mass is observed to be suppressed by ~40 MeV at nuclear matter density. Bound state searches are ongoing. This article gives an overview of the status of knowledge in this field together with an outlook to future experiments.
Status of the search for eta-mesic nuclei with particular focus on eta-Helium bound states
M. Skurzok
abstract
In this paper the search for eta-mesic nuclei with particular focus on light eta-He bound states is reviewed. A brief description of recent theoretical studies and experimental results is presented.
Search for the eta mesic 3He in the pd->dppi0 reaction with the WASA-at-COSY facility
P. Adlarson, ..., E. Czerwiński, A. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
The excitation function for the pd -> dppi0 reaction has been measured by WASA-at-COSY experiment with the aim of searching for 3He-eta mesic nuclei. The measurement in the vicinity of eta meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the eta-mesic Helium decays via the formation of an intermediate N*(1535) resonance. No direct signal of the eta-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the pd -> (3He-eta)bound -> dppi0 process. It varies between 13 nb to 24 nb for the bound state with width in the range Gamma (5,50) MeV.
Differential Cross Sections for Neutron-Proton Scattering in the Region of the d*(2380) Dibaryon Resonance
P. Adlarson, ..., E. Czerwiński, A. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Differential cross-sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized np scattering performed in the energy region of the d*(2380) dibaryon resonance covering the range of beam energies Tn=0.98?1.29 GeV (s=2.32?2.44 GeV). The experiment was carried out with the WASA-at-COSY setup having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp->np + p_spectator. In this way, the np differential cross-section sigma(theta) was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power Ay(theta) measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled D33-G33 waves
Three-nucleon dynamics in dp breakup collisions using the WASA detector at COSY-Jülich
P. Adlarson, ..., E. Czerwiński, A. Khreptak, W. Krzemień, P. Moskal, M. Skurzok, M.J. Zieliński, et al.
abstract
The differential cross section for the 1 H (d, pp)n breakup reaction at deuteron beam energy of 340 MeV
has been measured with the use of the WASA detector at COSY-Jülich. The set of proton-proton coincidences
registered at the Forward Detector has been analyzed on a dense grid of kinematic variables, giving in total
around 5600 data points. The cross-section data are compared to theoretical predictions based on the state-of-
the-art nucleon-nucleon potentials, combined with a three-nucleon force or the Coulomb interaction or carried
out in a relativistic regime.
Study of the N* momentum distribution for experimental eta-mesic 3He searches
N. G. Kelkar, D. Bedoya Fierro, H. Kamada, M. Skurzok
abstract
The proximity of the etaN threshold to the mass of the N*(1535) allows us to consider the eta-nucleus interaction below the eta threshold as a series of excitations, decays of the N* on the constituent nucleons and the eventual decay of the N* to a nucleon and a pion. Experimental searches for eta-mesic nuclei rely on this model in their analysis of data where an eta-mesic nucleus could have been formed. However, the momentum distribution of an N* is often approximated to be the same as that of a nucleon inside the nucleus. Our aim is to obtain an estimate of the error introduced by this assumption and hence we calculate the momentum distribution of the N* formed inside 3He. This distribution is found to be narrower than that of a nucleon inside 3He. The latter affects the outgoing particles kinematics and reduces the determined acceptance of their experimental registration by the detection setup. This reduction is crucial for the determination of cross sections in the search for eta-mesic helium.
Search for eta mesic 3He with the WASA-at-COSY facility in the pd-> 3He 2gamma and pd-> 3He 6gamma reactions
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
We report on the experimental search for the bound state of an eta meson and 3He nucleus performed using the WASA-at-COSY detector setup. In order to search for the eta-mesic nucleus decay, the pd->3He2gamma and pd->3He6gamma channels have been analysed. These reactions manifest the direct decay of eta meson bound in 3He nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to an 3He-eta nucleus width Gamma above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the eta-mesic 3He nucleus formation followed by the eta meson decay which varies between 2 nb and 15 nb depending on possible bound state parameters.
Non-mesonic decay of the eta-mesic 3He via pd->(3He-eta)bound 3He2gamma(6gamma) reaction
M. Skurzok, S. Hirenzaki, S. Kinutani, H. Konishi, P. Moskal, H. Nagahiro, O. Rundel
abstract
In this article a theoretical model for the eta-mesic 3He non-mesonic decay channels is presented. We present the resultant relative momentum distribution of bound 3He-eta as well as in-medium branching ratios of eta->2gamma and eta->3pi0, which are crucial for the Monte Carlo simulations of measured processes and thus for the experimental data interpretation. As an example we also apply the model for the estimation of the detection efficiency of the WASA-at-COSY detector.
Search for eta-mesic Helium with WASA-at-COSY
M. Skurzok
abstract
We report on the search for 4 He-eta and 3 He-eta mesic nuclei with WASA-at-COSY detection system. The description of the experimental method as well as recent status of the data analysis are presented.
Search for the 3He-eta Bound State via pd -> pdpi0 Reaction
A. Khreptak, M. Skurzok, O. Rundel
abstract
We present status and perspectives of the search for the eta-mesic helium nuclei via pd -> pdpi0 reaction with the WASA-at-COSY. In this report, the experimental method is shortly described and preliminary excitation function is presented.
Spectroscopy of eta'-mesic Nuclei with WASA at GSI/FAIR
Y.K. Tanaka, S. Bagchi, J. Benlliure, T. Dickel, V. Drozd, H. Ekawa, H. Fujioka, H. Geissel, F. Goldenbaum, C. Guo, E. Haettner, M.N. Harakeh, R.S. Hayano, S. Hirenzaki, C. Hornung, Y. Igarashi, N. Ikeno, K. Itahashi, M. Iwasaki, D. Jido, N. Kalantar-Nayestanaki, R. Kanungo, B. Kindler, R. Knöbel, D. Kostyleva, N. Kurz, N. Kuzminchuk, B. Lommel, Y. Ma, S.Y. Matsumoto, V. Metag, S. Minami, P. Moskal, I. Mukha, T. Nagae, H. Nagahiro, M. Nakagawa, H.J. Ong, H. Outa, S. Pietri, W.R. Plass, A. Prochazka, S. Purushothaman, C. Rappold, J. Ritman, J.L. Rodríguez-Sánchez, R. Ruber, O. Rundel, T.R. Saito, C. Scheidenberger, R. Sekiya, V. Serdyuk, H. Simon, B. Sitar, M. Skurzok, P. Strmen, B. Sun, I. Szarka, M. Takechi, I. Tanihata, S. Terashima, H. Weick, A. Yamamoto, J. Zhao
abstract
We plan to conduct an experimental search for eta'-mesic nuclei in order to investigate in-medium properties of the eta meson. A 2.5 GeV proton beam is employed to produce eta'-mesic 11C nuclei with the 12C(p,d) eta' at 11C reaction. Simultaneous measurements of the forward ejected deuterons and decay protons from eta'-mesic nuclei will allow us to achieve high experimental sensitivity. The experiment will be performed at GSI by making full use of the fragment separator FRS and the WASA detector system. The plan of this proposed experiment is described.
N-N-N* model calculations for experimental eta-mesic 3He searches
N. G. Kelkar, H. Kamada, M. Skurzok
abstract
The possibility for the existence of the exotic NNN* states is explored with the objective of calculating the N* momentum distribution inside such nuclei. Even though the latter is an essential ingredient for the analysis of the experimental data on the pd->pdpi0, pd->ppppi- and pd->pnnpi+ reactions aimed at finding an eta-mesic 3He, the data analysis is usually performed by approximating the N* momentum distribution by that of a nucleon. Here, we present calculations performed by solving the three-body Faddeev equations to obtain the momentum distribution of the N* inside possible (N* )+np, (N* )0np and (N* )+-d states. The N*
momentum distributions are found to be much narrower than those of the nucleons and influence the data selection criteria.
Etaprime and Eta Mesons with Connection to Anomalous Glue
S. D. Bass, P. Moskal
abstract
We review the present understanding of etaprime and eta meson physics and these mesons as a probe of gluon dynamics in low-energy QCD. Recent highlights include the production mechanism of eta and etaprime mesons in proton-nucleon collisions from threshold to high-energy, the etaprime effective mass shift in the nuclear medium, searches for possible eta and etaprime bound states in nuclei as well as precision measurements of eta decays as a probe of light-quark masses. We discuss recent experimental data, theoretical interpretation of the different measurements and the open questions and challenges for future investigation.
Examination of the Production of an Isotensor Dibaryon in the pp->pppi+pi- Reaction
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Exclusive measurements of the quasi-free pp->pppi+pi- reaction have been performed by means of pd collisions at Tp = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region Tp=1.08-1.36 GeV (sqrt(s) = 2.35 - 2.46 GeV), which includes the regions of N*(1440) and Delta(1232)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor DeltaN dibaryon resonance with I(JP)=2(1+) produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong and more recently calculated by Gal and Garcilazo.
Backward single-pion production in the pd->3Hepi0 reaction with WASA-at-COSY
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
New data on the production of single neutral pions in the pd->3Hepi0 reaction are presented. For fifteen proton beam momenta between pp=1.60GeV/c and pp=1.74GeV/c, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum.
Search for C violation in the decay eta->pi0 e+e- with WASA-at-COSY
P. Adlarson, ...,P. Moskal,...A. Pyszniak,..., Z. Rudy,..., M. Skurzok, et al. (WASA-at-COSY Collaboration)
abstract
We report on the investigation of the rare decay eta->pi0 e+e which is of interest to study both C violation in the electromagnetic interaction and to search for contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Juelich, Germany. In total 3×10^7 events of the reaction p+d->3He eta have been recorded at an excess energy of Q=59.8MeV. Based on this data set the C parity violating decay eta->pi0 g* -> pi0e+e- via a single-photon intermediate state has been searched for, resulting in new upper limits of Gamma(eta->pi0e+e-)/Gamma(eta->pi+pi-pi0)<3.28×10^-5 and Gamma(eta->pi0e+e-)/Gamma(eta-> all)<7.5×10^-6 (CL=90%), respectively.
Isotensor Dibaryon in the pp->pppi+pi- Reaction?
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Exclusive measurements of the quasi-free pp->pppi+pi- reaction have been carried out at WASA@COSY by means of pd collisions at Tp = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region Tp=1.08-1.36 GeV, which is the region of N*(1440) and Delta(1232)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor DeltaN dibaryon resonance with I(JP)=2(1+) produced associatedly with a pion is able to overcome these deficiencies.
Total and differential cross sections of eta-production in proton-deuteron fusion for excess energies between Q_eta=13MeV and Q_eta=81MeV
P. Adlarson, ...,E. Czerwiński, A. Khreptak, W. Krzemień, P. Moskal, O. Rundel, M. Skurzok, I. Schätti-Ozerianska, M. Zieliński, et al. (WASA-at-COSY Collaboration)
abstract
New data on both total and differential cross sections of the production of eta mesons in proton-deuteron fusion to 3He-eta in the excess energy region 13.6MeV < Q < 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p_p=1.60GeV/c and p_p=1.74GeV/c. While significant structure of the total cross section is observed in the energy region 20 MeV < Q < 60MeV, a previously reported sharp variation around Q ~ 50MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was reported elsewhere. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a large interval.
Constraining the optical potential in the search for eta-mesic 4He
M. Skurzok, P. Moskal, N.G. Kelkar, S. Hirenzaki, H. Nagahiro, N. Ikeno
abstract
A consistent description of the dd-> 4He eta and dd-> (4He-eta)bound X cross sections was recently proposed with a broad range of real (V0) and imaginary (W0), eta-4He optical potential parameters leading to a good agreement with the d d -> 4He eta data. Here we compare the predictions of the model below the eta production threshold, with the WASA-at-COSY excitation functions for the dd -> 3He N pi reactions to put stronger constraints on (V0, W0). The allowed parameter space (with |V_0| < sim 60 MeV and |W_0| < sim 7 MeV estimated at 90% CL ) excludes most optical model predictions of eta-4He nuclei except for some loosely bound narrow states.
Importance of d-wave contributions in the charge symmetry breaking reaction dd->4Hepi0
P. Adlarson, ...,E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, M. Skurzok, M. Zieliński et al. (WASA-at-COSY Collaboration)
abstract
This letter reports the first measurement of the contribution of higher partial waves in the charge symmetry breaking reaction dd->4Hepi0 using the WASA-at-COSY detector setup at an excess energy of Q=60 MeV. The determined differential cross section can be parametrized as dsigma/domega=a+bcos2theta?, where theta? is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a=(1.55+-0.46(stat)+0.32-0.8(syst))pb/sr and b=(13.1+-2.1(stat)+1.0-2.7(syst))pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the Delta isobar to the dd->4Hepi0 reaction and is therefore crucial for a quantitative understanding of quark mass effects in nuclear production reactions.
Spin dependence of eta meson production in proton-proton collisions close to threshold
P. Adlarson, ...,E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, M. Skurzok, M. Zieliński et al. (WASA-at-COSY Collaboration)
abstract
Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and
the high degree of the polarized proton beam of COSY, the reaction ~pp->pp eta has been measured
close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined
with the precision improved by more than one order of magnitude with respect to previous results
allowing a first accurate comparison with theoretical predictions. The determined analyzing power
is consistent with zero for an excess energy of Q=15 MeV signaling s wave production with no
evidence for higher partial waves. At Q=72 MeV the data reveals strong interference of Ps and
Pp partial waves and cancellation of (Pp) and Ss?Sd contributions. These results rule out the
presently available theoretical predictions for the production mechanism of the eta meson.
Isoscalar single-pion production in the region of Roper and d*(2380) resonances
P. Adlarsona, W. Augustyniak, W. Bardan, M. Bashkanov, FS. Bergmann, M. Berlowski, H. Bhatt, A. Bondar, M. Buscher, H. Calen, I. Ciepal, H. Clement, E. Czerwinski, K. Demmich, R. Engels, A. Erven, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, A. Goswami, K. Grigoryev, CO. Gullstrom, L. Heijkenskjold, V. Hejny, N. Husken, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, G. Khatri, A. Khoukaz, O. Khreptak, DA. Kirillov, S. Kistryn, H. Kleines, B. Klos, W. Krzemien, P. Kulessa, A. Kupsc, A. Kuzmin, K. Lalwani, D. Lersch, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, HP. Morsch, P. Moskal, H. Ohm, W. Parol, EP. del Rio, NM. Piskunov, D. Prasuhn, D. Pszczel, K. Pysz, A. Pyszniak, J. Ritman, A. Roy, Z. Rudy, O. Rundel, S. Sawant, S. Schadmand, I. Schatti-Ozerianska, T. Sefzick, et al.
abstract
Exclusive measurements of the quasi-free pn -> pp pi(-) and pp -> pp pi(0) reactions have been performed by means of pd collisions at T-p= 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region T-p= 0.95-1.3 GeV (root s = 2.3-2.46 GeV), which includes the regions of triangle(1232), N*(1440) and d*(2380) resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below T-p = 1 GeV. We observe a substantial increase of this cross section around 1 GeV, which can be related to the Roper resonance N*(1440), the strength of which shows up isolated from the triangle resonance in the isoscalar (N pi)(I=0) invariant-mass spectrum. No evidence for a decay of the dibaryon resonance d*(2380) into the isoscalar (NN pi)(I=0) channel is found. An upper limit of 180 mu b (90% CL.) corresponding to a branching ratio of 9% has been deduced. (c) 2017 The Author(s). Published by Elsevier B.V.
Search for the eta-mesic Helium in Proton-Deuteron Reaction
O. Rundel, M. Skurzok, O. Khreptak, P. Moskal
abstract
We briefly report on the search for eta-mesic helium nuclei with WASA-at-COSY detection setup. The description of the experimental method as well as the status of the data analysis of the proton?deuteron reactions are presented.
The pd -> eta 3He Reaction and eta 3He Bound State? The B*B*rho System
E. Oset, J.J. Xie, W.H. Liang, P. Moskal, M. Skurzok, C. Wilkin, M. Bayar, P. Fernandez Soler, Z.F. Sun
abstract
We analyze the data on cross sections and asymmetries for the pd(dp) -> eta 3He reaction close to threshold and look for bound states of the eta 3He system. Fitting these data in terms of an eta 3He optical potential, we find a local Breit?Wigner form of the eta 3He amplitude T below threshold with a clear peak in |T|2, which corresponds to an eta 3He binding of about 0.3 MeV and a width of about 3 MeV. However, this corresponds to a pole in the complex plane above threshold. We also discuss a state found for BB*rho with J = 3.
Measurement of the omega->pi+pi-pi0 Dalitz plot distribution
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Using the production reactions pd->3Heomega and pp->pp omega, the Dalitz plot distribution for the omega->pi+pi-pi0 decay is studied with the WASA detector at COSY, based on a combined data sample of (4.408+-0.042)*10^4 events. The Dalitz plot density is parametrised by a product of the P-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables Z and phi. For the first time, a deviation from pure P-wave phase space is observed with a significance of 4.1 sigma. The deviation is parametrised by a linear term 1+2 alpha Z, with alpha determined to be +0.147+-0.036, consistent with the expectations of rho-meson-type final-state interactions of the P-wave pion pairs.
Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3Henpi0 and dd->3Hepi- processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd-> 4He eta reaction ranging from Q = -70 MeV to Q = 30 MeV. The luminosity was determined based on the dd-> 3Hen reaction and the quasi-free proton-proton scattering via dd -> ppn_spectator n_spectator reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd->(4He-eta)bound->3Henpi0 and dd->(4He-eta)bound->3Hepi- processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N*(1535) momentum distribution in the anticipated mesic-4He. Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in 4He, we determined that (for the mesic bound state width in the range
from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for npi0 and p pi- channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N* -3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for n pi0 and p pi- channels respectively.
Determination of the eta 3He threshold structure from the low energy pd -> eta 3He reaction
J.-J. Xie, W.-H. Liang, E. Oset, P. Moskal, M. Skurzok and C. Wilkin
abstract
We analyze the data on cross sections and asymmetries for the pd(dp) -> eta 3He reaction close to threshold and look for bound states of the eta 3He system. Rather than parameterizing the scattering matrix, as is usually done, we develop a framework in which the eta 3He optical potential is the key ingredient, and its strength, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the eta 3He loop function incorporates the range of the interaction given by the empirical 3He density. We find a local Breit Wigner form of the eta 3He amplitude T
below threshold with a clear peak in |T|^2 , which corresponds to an eta binding of about 0.3 MeV and a width of about 3 MeV. By fitting the potential we can also evaluate the eta 3He scattering length, including its sign, thus resolving the ambiguity in the former analyses.
Measurements of branching ratios for eta decays into charged particles
P. AdlarsoN, W. Augustyniak, W. Bardan, M. Bashkanov, FS. Bergmann, M. Berlowski, H. Bhatt, A. Bondar, M. Buscher, H. Calen, I. Ciepal, H. Clement, D. Coderre, E. Czerwinski, K. Demmich, R. Engels, A. Erven, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, A. Goswami, K. Grigoryev, CO. Gullstrom, L. Heijkenskjold, V. Hejny, N. Husken, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, FA. Khan, G. Khatri, A. Khoukaz, DA. Kirillov, S. Kistryn, H. Kleines, B. Klos, W. Krzemien, P. Kulessa, A. Kupsc, A. Kuzmin, K. Lalwani, D. Lersch, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, M. Mikirtychiants, HP. Morsch, P. Moskal, H. Ohm, I. Ozerianska, EP. del Rio, NM. Piskunov, D. Prasuhn, D. Pszczel, K. Pysz, A. Pyszniak, J. Ritman, A. Roy, Z. Rudy, O. Rundel, S. Sawant, S. Schadmand, et al.
abstract
The WASA-at-COSY experiment has collected 3 x 10(7) events with eta mesons produced via the reaction pd -> He-3 eta at T = 1.0 GeV. Using this data set, we evaluate the branching ratios of the decays eta -> pi(+)pi(-)gamma, eta -> e(+)e(-)gamma, eta -> pi(+)pi(-)e(+)e(-), and eta -> e(+)e(-)e(+)e(-). The branching ratios are normalized to the eta -> pi(+)pi(-) pi(0) decay. In addition an upper limit on a CP-violating asymmetry in eta -> pi(+)pi(-)e(+)e(-) is extracted.
Search for an Isospin I =3 Dibaryon
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d*(2380) with I(JP)=0(3+) there should also exist a dibaryon resonance with mirrored quantum numbers I(JP)=3(0+). We report here on a search for such a NN-decoupled state in data on the pp -> pp pi+ pi+ pi- pi- reaction.
On Quasibound N*-Nuclei
N. G. Kelkar, D. Bedoya Fierro, P. Moskal
abstract
The possibility for the existence of unstable bound states of the S11 nucleon resonance N?(1535) and nuclei is investigated. These quasibound states are speculated to be closely related to the existence of the quasibound states of the eta mesons and nuclei. Within a simple model for the NN? interaction involving a pion and eta meson exchange, N??nucleus potentials for N??3He and N??24Mg are evaluated and found to be of a Woods?Saxon-like form which supports two to three bound states. In the case of N??3He, one state bound by only a few keV and another by 4 MeV is found. The results are however quite sensitive to the NN?? and NN?? vertex parameters. A rough estimate of the width of these states, based on the mean free path of the exchanged mesons in the nuclei, leads to very broad states with ? ? 80 and 110 MeV for N??3He and N??24Mg respectively.
Upper limits for the production of the eta-mesic Helium in the dd ->3Henpi0 and dd -> 3Heppi- reactions
M. Skurzok, W. Krzemień, O. Rundel, P. Moskal
abstract
We performed a search for 4 He-eta bound state in dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility using a ramped beam technique. The measurement was carried out with high statistics and high acceptance. The signature of eta-mesic nuclei was searched for by the measurement of the excitation functions in the vicinity of the eta production threshold for each of the considered channels. We did not observe the narrow structure which could be interpreted as a bound state. The preliminary upper limits of the total cross sections for the bound state production and decay varies from 21 nb to 36 nb for the dd->3He n pi0 channel, and from 5 nb to 9 nb for the dd->3He p pi- channel for the bound state width ranging from 5 to 50 MeV.
Measurement of the vec{n} p->d pi0 pi0 Reaction with Polarized Beam in the Region of the d*(2380) Resonance
P. Adlarson, ..., E. Czerwiński, M. Hodana, J. Klaja, W. Krzemień, P. Moskal, I. Ozerianska, O. Rundel, M. Skurzok, M. Zieliński et al.
abstract
We report on a high-statistics measurement of the most basic double pionic fusion reaction vec{n}p -> dpi0pi0 over the energy region of the d*(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d? resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
Search for eta-mesic Nuclei with WASA-at-COSY
W. Krzemień, P. Moskal, M. Skurzok
abstract
We search for an evidence of ?-mesic He with the WASA detector. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Jülich. The experimental method is based on the measurement of the excitation functions for the two reaction channels: dd ?3He p?? and dd ?3He n?0, where the outgoing N?? pairs originate from the conversion of the ? meson on a nucleon inside the He nucleus. In this contribution, the experimental method is shortly described and the current status of the analysis is presented.
Luminosity determination for the deutron-deutron reactions using free and quasi-free reactions with WASA-at-COSY detector
M. Skurzok, P. Moskal, W. Krzemień
abstract
Two methods of the luminosity determination for the experiment performed by WASA col- laboration to search for 4He-eta bound state are presented. During the measurement the tech- nique of continous change of the beam momentum in one accelerator cycle (called ramped beam) was applied. This imposes the requirement to determine not only the total integrated luminosity, but also its variation as a function of the beam momentum.
Determination of the COSY Proton Beam Polarization Using the WASA Detector
I. Schätti-Ozerianska, P. Moskal, M. Zieliński
abstract
The dynamics of ?-meson production and the interaction of ? mesons with nucleons can be studied using the pp ? pp? reaction via measurements of the analyzing power Ay. To this end, we have performed a measurement of the pp ? pp? reaction using the WASA-at-COSY detector, which provides large acceptance and is ?-symmetric. The experiment was carried out for the beam momenta of 2026 MeV/c and 2188 MeV/c. In this article, we present a method and results for the determination of the degree of the beam polarization.
ABC Effect and Resonance Structure in the Double-Pionic Fusion to 3He
P. Adlarson, ..., E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zielinski, et al.
abstract
Exclusive and kinematically complete measurements of the double pionic fusion to 3He have been performed in the energy region of the so-called ABC effect, which denotes a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY. Similar to the observations in the basic pn->dpi0pi0 reaction and in the dd->4Hepi0pi0 reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. Differential cross sections are well described by the hypothesis of d* resonance formation during the reaction process in addition to the conventional t-channel Delta Delta mechanism. The deduced d* resonance width can be understood from collision broadening due to Fermi motion of the nucleons in initial and final nuclei.
Study of the polarization degree for the -> p p ->pp eta measurement with WASA
I. Ozerianska, P. Moskal, M. Hodana
abstract
Understanding of the production processes of the eta meson will strongly rely on the precise determination of spin observables. So far these observables have been determined only for few excess energies and with low statistics (Winter et al. Eur. Phys. J. A18, 355 2003; Czyzykiewicz et al. Phys. Rev. Lett. 98, 122003 2007; Balestra et al. Phys. Rev. C69, 064003 2004). In the year 2010 WASA detector was used for the measurement of the p?p?pp? reaction with the polarized proton beam of COSY (Moskal and Hodana J. Phys. Conf. Ser 295, 012080 2011). The measurement was done for the excess energy of Q = 15 MeV and Q = 72 MeV. In total about 106 events corresponding to the p?p?pp? reaction have been collected.
Measurement of the np->npi0i0 Reaction in Search for the Recently Observed d*(2380) Resonance
P. Adlarson,..., E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zielinski, et al.
abstract
Exclusive measurements of the quasi-free np->nppi0pi0 reaction have been performed by means of dp collisions at Td = 2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region sqrt_s = (2.35 - 2.46) GeV, which includes the region of the ABC effect and its associated d*(2380) resonance. Adding the d* resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Faeldt and Wilkin as well Albadajedo and Oset. The ABC effect, {it i.e.} the low-mass enhancement in the pi0pi0-invariant mass spectrum, is found to be very modest - if present at all, which might pose a problem to some of its interpretations.
Neutron-Proton Scattering in the Context of the d*(2380) Resonance
P. Adlarson, ..., E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zielinski, et al.
abstract
New data on quasifree polarized neutron-proton scattering, in the region of the recently observed d* resonance structure, have been obtained by exclusive and kinematically complete high-statistics measurements with WASA at COSY. This paper details the determination of the beam polarization, checks of the quasifree character of the scattering process, on all obtained Ay angular distributions and on the new partial-wave analysis, which includes the new data producing a resonance pole in the 3D3-3G3 coupled partial waves at (2380+-10-i40+-5) MeV -- in accordance with the d* dibaryon resonance hypothesis. The effect of the new partial-wave solution on the description of total and differential cross section data as well as specific combinations of spin-correlation and spin-transfer observables available from COSY-ANKE measurements at Td = 2.27 GeV is discussed.
Charge Symmetry Breaking in dd->4Hepi0 with WASA-at-COSY
P. Adlarson, ..., E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zielinski, et al.
abstract
Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4He{pi}0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13(sys) +- 8(ext)) pb and first data on the differential cross section are consistent with s-wave pion production.
Cross section ratio and angular distributions of the reaction p + d -> (3)He + eta at 48.8 MeV and 59.8 MeV excess energy
P. Adlarson, E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zielinski, et al.
abstract
We present new data for angular distributions and on the cross section ratio of the p+d -> (3)He + eta reaction at excess energies of Q = 48.8 MeV and Q = 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum Jülich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.
Measurement of the eta -> pi + pi - pi0 Dalitz plot distribution
P. Adlarson,..., E. Czerwiński, M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zieliński, et al.
abstract
Dalitz plot distribution of the eta-> pi+pi-pi0 decay is determined using a data sample of 1.2*10^7 eta mesons from pd->3He eta reaction at 1 GeV collected by the WASA detector at COSY.
Evidence for a New Resonance from Polarized Neutron-Proton Scattering
P. Adlarson, ..., E. Czerwiński, M. Hodana, J. Klaja, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zieliński et al.
abstract
Exclusive and kinematically complete high-statistics measurements of quasifree polarized vec_n p scattering have been performed in the energy region of the narrow resonance structure d* with I(JP)=0(3+), M ~2380 MeV/c2 and Gamma 70 MeV observed recently in the double-pionic fusion channels pn->dpi0pi0 and pn->dpi+pi-. The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process d p->np+p_spectator. That way the np analyzing power Ay was measured over a large angular range. The obtained Ay angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new Ay data into the SAID analysis produces a pole in the 3D3->3G3 waves as expected from the d* resonance hypothesis.
Few-body aspects of the near threshold pseudoscalar meson production
P. Moskal
abstract
During last decade large samples of data have been collected on the production of the ground-state pseudoscalar mesons in collisions of proton or deuteron beam with hydrogen or deuterium target. These measurements have been performed in the vicinity of the kinematical threshold for meson production where only a few partial waves in both initial and final state are expected to contribute to the production process. This simplifies significantly the interpretation of the data, yet still appears to be challenging due to the three or four particle final state systems with a complex hadronic potential. We review experiments and phenomenology of the near threshold production of the ground-state mesons in the few-body final states as for example: nucleus-meson and nucleon-nucleon-meson, and report on the status of the search of the mesic-nuclei (a meson-nucleus bound states). Experimental advantages of measurements close to the kinematical threshold are discussed, and general features of the production mechanism of the eta and eta prime mesons in the nucleon-nucleon collisions are presented emphasising results of measurements of spin and izospin dependence of the production cross sections.
Study of the eta meson production with polarized proton beam
M. Hodana, P. Moskal, I. Ozerianska, M. Zieliński
abstract
The pp-> pp eta reaction was investigated at excess energies of 15 MeV and 72 MeV using the azimuthally symmetric WASA detector and a polarized proton beam of the Cooler Synchrotron COSY. The aim of the studies is the determination of partial wave contributions to the production process of the eta meson in nucleon-nucleon collisions. Here we present preliminary results of the extraction of the position of the interaction region with respect to the WASA detector and preliminary results on the degree of polarization of the COSY proton beam used in the experiment.
Search for the manifestation of the mesic-nuclei on the dd-->3HeNpi excitation function measured with WASA-at-COSY
W. Krzemień, P. Moskal, M. Skurzok
abstract
We search for an evidence of eta-mesic 4He with the WASA-at-COSY detector. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Juelich. The experimental method is based on the measurement of the excitation functions for the two reaction channels: dd-->3Heppi- and dd-->3Henpi0, where the outgoing N-pi pairs originate from the conversion of the eta meson on a nucleon inside the He nucleus. In this contribution, the experimental method is shortly described and preliminary excitation functions from the 2010 data are presented.
Search for eta-Mesic 4He with WASA-at-COSY
W. Krzemien, P. Moskal, M. Skurzok
abstract
An exclusive measurement of the excitation functions for the dd ->3He p ?- and dd -> 3He n ?0 -> 3He n gamma gamma reactions was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were collected in two dedicated experiments in 2008 and in 2010. The experimental method and the current status of the analysis are presented.
COSY Proposal/Beam Request: Search for the eta -mesic 3He with WASA at COSY
P. Moskal, W. Krzemien, M. Skurzok
abstract
We propose to conduct a search for the 3He-eta bound state by the energy scan at the final states ppNpi, 3He6gamma and 3He2gamma measuring excitation functions of its production cross section in proton-deuteron reactions for processes corresponding to two anticipated mechanisms: (i) absorption of the eta meson by one of the nucleons, which subsequently decays into N-pi pair e.g.: pd-> (3He-eta)bound ->ppppi- , and (ii) decay of the eta-meson while it is still orbiting around a nucleus e.g.: pd-> (3He-eta)bound -> 3He6gamma reactions. This sproposal has been accepted in PAC Session No. 42 II/2013 and experiment (Exp. No. 186.3) was carried out in May 2014.
Measurement of the pn->pp pi0pi- Reaction in Search for the Recently Observed Resonance Structure in dpi0pi0 and dpi+pi-systems
P. Adlarson, ..., E. Czerwiński, M. Hodana, J. Klaja, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zieliński et al.
abstract
Exclusive measurements of the quasi-free $pn o pppi^0pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $sqrt s$ = (2.35 - 2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. No ABC effect, {it i.e.} low-mass enhancement is found in the $pi^0pi^-$-invariant mass spectrum -- in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s-wave. At the upper end of the covered energy region $t$-channel processes for Roper, $Delta(1600)$ and $DeltaDelta$ excitations provide a reasonable description of the data, but at low energies the measured cross sections are much larger than predicted by such processes. Adding a resonance amplitude for the resonance at $m$=~2.37 GeV with $Gamma$ =~70 MeV and $I(J^P)=~0(3^+)$ observed recently in $pn o dpi^0pi^0$ and $pn o dpi^+pi^-$ reactions leads to an agreement with the data also at low energies.
Isospin decomposition of the basic double-pionic fusion in the region of the ABC effect
P. Adlarson, W. Augustyniak, W. Bardan, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, K. Demmich, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, A. Goswami, K. Grigoryev, CO. Gullstrom, F. Hauenstein, L. Heijkenskjold, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, FA. Khan, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, M. Krapp, W. Krzemien, P. Kulessa, A. Kupsc, K. Lalwani, D. Lersch, L. Li, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, M. Mikirtychiants, HP. Morsch, P. Moskal, BK. Nandi, S. Niedzwiecki, H. Ohm, I. Ozerianska, EP. del Rio, P. Plucinski, P. Podkopal, et al.
abstract
Exclusive and kinematically complete high-statistics measurements of the basic double-pionic fusion reactions pn -> d pi(0)pi(0), pn -> d pi(+)pi(-) and pp -> d pi(+)pi(0) have been carried out simultaneously over the energy region of the ABC effect using the WASA detector setup at COSY. Whereas the isoscalar reaction part given by the d pi(0)pi(0) channel exhibits the ABC effect, i.e. a low-mass enhancement in the pi pi-invariant mass distribution, as well as the associated resonance structure in the total cross section, the isovector part given by the d pi(+)pi(0) channel shows a smooth behavior consistent with the conventional t-channel Delta Delta process. The d pi(+)pi(-) data are very well reproduced by combining the data for isovector and isoscalar contributions, if the kinematical consequences of the isospin violation due to different masses for charged and neutral pions are taken into account. (C) 2013 Elsevier B.V. All rights reserved.
Investigation of the dd -> 3henpi0 reaction with the FZ Jülich WASA-at-COSY facility
P. Adlarson, ..., W. Bardan, I. Ciepał, E. Czerwiński, M. Hodana, J. Klaja, W. Krzemień, I. Ozerianska, P. Moskal, M. Skurzok,M. Zieliński, et al.
abstract
An exclusive measurement of the dd?3Hen?0 reaction was carried out at a beam momentum of pd= 1.2 GeV/c using the WASA-at-COSY facility. Information on the total cross section as well as differential distributions was obtained. The data are described by a phenomenological approach based on a combination of a quasifree model and a partial wave expansion for the three-body reaction. The total cross section is found to be ?tot=(2.89?0.01stat?0.06sys?0.29norm) ?b. The contribution of the quasifree processes (with the beam or target neutron being a spectator) accounts for 38% of the total cross section and dominates the differential distributions in specific regions of phase space. The remaining part of the cross section can be described by a partial wave decomposition indicating the significance of p-wave contributions in the final state.
Search for a dark photon in the pi0->e+e-gamma decay
P. Adlarson, ..., M. Hodana, W. Krzemień, P. Moskal, I. Ozerianska, M. Skurzok, M. Zieliński et al.
abstract
The presently world largest data sample of pi0 --> gamma e+e- decays containing nearly 5E5 events was collected using the WASA detector at COSY. A search for a dark photon U produced in the pi0 --> gamma U --> gamma e+e- decay from the pp-->pppi^0 reaction was carried out. An upper limit on the square of the U-gamma mixing strength parameter epsilon^2 of 5e-6 at 90% CL was obtained for the mass range 30 MeV
Search for the eta-mesic 4He with WASA-at-COSY detector
P. Adlarson, W. Augustyniak, W. Bardan, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, K. Demmich, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, A. Goswami, K. Grigoryev, CO. Gullstrom, F. Hauenstein, L. Heijkenskjold, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, FA. Khan, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, M. Krapp, W. Krzemien, P. Kulessa, A. Kupsc, K. Lalwani, D. Lersch, L. Li, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, M. Mikirtychiants, HP. Morsch, P. Moskal, BK. Nandi, S. Niedzwiecki, H. Ohm, I. Ozerianska, EP. del Rio, P. Plucinski, P. Podkopal, et al.
abstract
An exclusive measurement of the excitation function for the dd->3Heppi- reaction was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta meson production in the dd->4He-eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the 4He-eta system varied from -51.4MeV to 22MeV. The integrated luminosity in the experiment was determined using the dd->3Hen reaction. The shape of the excitation function for the dd->3Heppi- was examined. No signal of the 4He-eta bound state was observed. An upper limit for the cross-section for the bound state formation and decay in the process dd->(4He-eta)bound->3Heppi- was determined on the 90% confidence level and it varies from 20nb to 27nb for the bound state width ranging from 5MeV to 35MeV, respectively.
Abashian-Booth-Crowe resonance structure in the double pionic fusion to He-4
P. Adlarson, W. Augustyniak, W. Bardan, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, KT. Brinkmann, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, K. Demmich, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, K. Grigoryev, CO. Gullstrom, F. Hauenstein, L. Heijkenskjold, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, C. Husmann, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, FA. Khan, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, W. Krzemien, P. Kulessa, A. Kupsc, K. Lalwani, D. Lersch, L. Li, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, M. Mikirtychiants, HP. Morsch, P. Moskal, BK. Nandi, S. Niedzwiecki, H. Ohm, I. Ozerianska, C. Pauly, EP. del Rio, Y. Petukhov, et al.
abstract
Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction dd?4He?0?0 have been performed in the energy range 0.8?1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the ?? invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic pn?d?0?0 reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at m=2.37 GeV + 2mN, i.e., at the same position as in the basic reaction. The observed resonance width ??160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a pn resonance formation during the reaction process.
Exclusive measurement of the eta->pi+ pi- gamma decay
P. Adlarson, C. Adolph, W. Augustyniak, W. Bardan, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, KT. Brinkmann, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, K. Grigoryev, CO. Gullstrom, C. Hanhart, L. Heijkenskjold, J. Heimlich, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, M. Jacewicz, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, O. Khakimova, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, F. Kren, W. Krzemien, P. Kulessa, A. Kupsc, K. Lalwani, S. Leupold, B. Lorentz, A. Magiera, R. Maier, B. Marianski, P. Marciniewski, UG. Meissner, M. Mikirtychiants, HP. Morsch, P. Moskal, BK. Nandi, S. Niedzwiecki, H. Ohm, A. Passfeld, C. Pauly, et al.
abstract
An exclusive measurement of the decay eta --> pi+ pi- gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd --> 3He X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13340pm140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta --> pi+ pi- gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi+ pi- system.
Search for the He-eta bound states with the WASA-at-COSY facility
M. Skurzok, P. Moskal, W. Krzemień
abstract
The existence of eta-mesic nuclei in which the eta meson is bound in a nucleus by means of the strong interaction was postulated already in 1986, albeit not yet confirmed it by experiment. The discovery of this new kind of an exotic nuclear matter would be very important as it might allow for a better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium (4He-eta) is carried out with high statistics and high acceptance with the WASA detector, installed at the cooler synchrotron COSY of the Research Center Juelich. The search is conducted via the measurement of the excitation function for selected decay channels of the 4He-eta system. In the experiment, performed in November 2010, two reactions dd -> (4He-eta)bs -> 3He p pi- and dd -> (4He-eta)bs -> 3He n pi0 were measured with a beam momentum ramped from 2.127GeV/c to 2.422GeV/c. The report includes the description of the experimental method and status of the measurement.
pi0 pi0 Production in proton-proton collisions at Tp=1.4 GeV
P. Adlarson, C. Adolph, W. Augustyniak, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, KT. Brinkmann, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, K. Grigoryev, CO. Gullstrom, L. Heijkenskjold, J. Heimlich, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, M. Jacewicz, M. Janusz, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, O. Khakimova, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, F. Kren, W. Krzemien, P. Kulessa, A. Kupsc, K. Lalwani, B. Lorentz, A. Magiera, R. Maier, B. Marianski, P. Marciniewski, M. Mikirtychiants, HP. Morsch, P. Moskal, BK. Nandi, S. Niedzwiecki, H. Ohm, A. Passfeld, C. Pauly, EP. del Rio, Y. Petukhov, N. Piskunov, et al.
abstract
The reaction pp->pppi0pi0 has been investigated at a beam energy of 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 +- 21_systematic +- 58_normalization) mub. In order to to study the production mechanism, differential kinematical distributions have been evaluated. The differential distributions indicate that both initial state protons are excited into intermediate Delta(1232) resonances, each decaying into a proton and a single pion, thereby producing the pion pair in the final state. No significant contribution of the Roper resonance N*(1440) via its decay into a proton and two pions is found
Studies of the eta meson with WASA at COSY and KLOE-2 at DAFNE
P. Moskal
abstract
One of the basic motivations of the KLOE-2 and WASA-at-COSY experiments
is the test of fundamental symmetries and the search for phenomena beyond the
Standard Model in the hadronic and leptonic decays of ground-state mesons and in
particular in decays of the eta meson. At COSY these mesons are produced in collisions
of proton or deuteron beam with hydrogen or deuterium pellet target, and at
DAFNE eta mesons originate from radiative decays of fi meson or from the fusion of
virtual gamma quanta exchanged between colliding electrons and positrons. This
contribution includes brief description of experimental techniques used by KLOE-2
and WASA-at-COSY as well as some of physics aspects motivating investigations
of production and decays of ? mesons.
Abashian-Booth-Crowe effect in basic double fusion: A new resonance?
P. Adlarson, C. Adolph, W. Augustyniak, V. Baru, M. Bashkanov, T. Bednarski, FS. Bergmann, M. Berlowski, H. Bhatt, KT. Brinkmann, M. Buscher, H. Calen, H. Clement, D. Coderre, E. Czerwinski, E. Doroshkevich, C. Ekstrom, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Fohl, K. Fransson, F. Goldenbaum, P. Goslawski, K. Grigoryev, V. Grishina, CO. Gullstrom, J. Hampe, C. Hanhart, L. Heijkenskjold, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, M. Jacewicz, M. Janusz, A. Jany, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, O. Khakimova, A. Khoukaz, S. Kistryn, J. Klaja, H. Kleines, B. Klos, F. Kren, W. Krzemien, P. Kulessa, S. Kullander, A. Kupsc, K. Lalwani, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski, M. Mikirtychiants, P. Moskal, HP. Morsch, BK. Nandi, S. Niedzwiecki, H. Ohm, et al.
abstract
We report on an exclusive and kinematically complete high-statistics measurement of the basic double-pionic fusion reaction pn->dpi0pi0 over the full energy region of the ABC effect, a pronounced low-mass enhancement in the pipi-invariant mass spectrum. The measurements, which cover also the transition region to the conventional t-channel DeltaDelta process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance with m=2.37??GeV, Gamma aprox 70 MeV and I(JP)=0(3+) in both pn and DeltaDelta systems. Necessary further tests of the resonance interpretation are discussed.
Measurement of the eta->pi+pi-pi0 decay with WASA-at-COSY detector
P. Adlarson, M. Zieliński
abstract
One of the objectives of the physics programme of the WASA-at-COSY facility is to study the isospin violating eta hadronic decays into pi+pi-pi0 systems driven by the term of QCD Lagrangian which depends on the d and u quark mass difference. These studies can be made in terms of the Dalitz plot parameters describing the density population which is proportional to the square of the amplitude |A(x, y)|2. This contribution describes the current status of the analysis of the eta->pi+pi-pi0 decay in the pd->3He-eta and as well in the pp->pp-eta reaction with WASA-at-COSY.
Study of the eta --> e+e-gamma decay with the WASA-at-COSY
M. Hodana
abstract
In October 2008, the WASA-at-COSY collected more than 107 events for the pd-->3He reaction. The aim is the determination of the invariant mass of the lepton pairs created in the Dalitz decay eta --> e+e-gamma. The e+e- invariant mass spectrum is directly related to the distribution of the four-momentum squared of the virtual photon from the eta-->gamma*gamma process and hence it allows for the study of the transition form factor which in turn reflects the structure of the decaying meson.
Search for the eta-mesic nuclei by means of COSY-11, WASA-at-COSY and COSY-TOF detector systems
P. Moskal, J. Smyrski
abstract
We review status and perspectives of the search for the light eta-mesic nuclei using COSY-11, WASA-at-COSY and COSY-TOF detector systems.
Measurement of the eta->3pi0 Dalitz plot distribution with the WASA detector at COSY
WASA-at-COSY Collaboration: C. Adolph, ..., E. Czerwiński, R. Czyżykiewicz, M. Hodana, M. Janusz, J. Klaja, P. Klaja, W. Krzemień, P. Moskal, M. Zieliński, et al.
abstract
In the first production run of the WASA experiment at COSY, the eta decay into three neutral pions was measured in proton?proton interactions at a proton beam kinetic energy of 1.4 GeV. The Dalitz plot of the three pions was studied using fully reconstructed events, and the quadratic slope parameter ? was determined to be . The result is consistent with previous measurements and further corroborates the importance of pion?pion final state interactions.
Studies of three-and four-body hypernuclei with heavy-ion beams, nuclear emulsions and machine learning
T.R. Saito, P. Achenbach, H. Alibrahim Alfaki, F. Amjad, M. Armstrong, K.-H. Behr, J. Benlliure, Z. Brencic, T. Dickel, V. Drozd, S. Dubey, H. Ekawa, S. Escrig, M. Feijoo-Fontan, Y. Gao, H. Geissel, F. Goldenbaum, A. Grana Gonzalez, E. Haettner, M. N. Harakeh, Y. He, H. Heggen, C. Hornung, N. Hubbard, K. Itahashi, N. Kalantar-Nayestanaki, A. Kasagi, M. Kavatsyuk, E. Kazantseva, A. Khreptak, R. Knoebel, H. Kollmus, D. Kostyleva, S. Kraft-Bermuth, N. Kurz, E. Liu, S. Minami, D.J. Morrissey, P. Moskal, I. Mukha, A. Muneem, M. Nakagawa, K. Nakazawa, C. Nociforo, H. J. Ong, S. Pietri, J. Pochodzalla, S. Purushothaman, C. Rappold, E. Rocco, J.L. Rodriguez-Sanchez, P. Roy, R. Ruber, N. Saito, S. Schadmand, C. Scheidenberger, P. Schwarz, R. Sekiya, V. Serdyuk, M. Skurzok, B. Streicher, S. Sugimoto, K. Suzuki, B. Szczepanczyk, M. Taki, Y.K. Tanaka, X. Tang, N. Tortorelli, M. Vencelj, H. Wang, T. Weber, H. Weick, M. Will, K. Wimmer, A. Yamamoto, A. Yanai, J. Yoshida, M. Yoshimoto, J. Zhao
abstract
Interests on few-body hypernuclei have been increased by recent results of experiments employing relativistic heavy ion beams. Some of the experiments have revealed that the lifetime of the lightest hypernucleus, hypertriton, is significantly shorter than 263 ps which is expected by considering the hypertriton to be a weakly-bound system. The STAR collaboration has also measured the hypertriton binding energy, and the deduced value is contradicting to its formerly known small binding energy. These measurements have indicated that the fundamental physics quantities of the hypertriton such as its lifetime and binding energy have not been understood, therefore, they have to be measured very precisely. Furthermore, an unprecedented ?nn bound state observed by the HypHI collaboration has to be studied in order to draw a conclusion whether or not such a bound state exists. These three-body hypernuclear states are studied by the heavy-ion beam data in the WASA-FRS experiment and by analysing J-PARC E07 nuclear emulsion data with machine learning.
WASA-FRS Experiments in FAIR Phase-0 at GSI
Y.K. Tanaka, P. Achenbach, H. Alibrahim Alfaki, F. Amjad, M. Armstrong, K.-H. Behr, J. Benlliure, Z. Brencic, T. Dickel, V. Drozd, S. Dubey, H. Ekawa, S. Escrig, M. Feijoo-Fontán, H. Fujioka, Y. Gao, H. Geissel, F. Goldenbaum, A. Gra?a González, E. Haettner, M.N. Harakeh, Y. He, H. Heggen, C. Hornung, N. Hubbard, K. Itahashi, M. Iwasaki, N. Kalantar-Nayestanaki, A. Kasagi, M. Kavatsyuk, E. Kazantseva, A. Khreptak, B. Kindler, R. Knoebel, H. Kollmus, D. Kostyleva, S. Kraft-Bermuth, N. Kurz, E. Liu, B. Lommel, V. Metag, S. Minami, D.J. Morrissey, P. Moskal, I. Mukha, A. Muneem, M. Nakagawa, K. Nakazawa, C. Nociforo, H.J. Ong, S. Pietri, J. Pochodzalla, S. Purushothaman, C. Rappold, E. Rocco, J.L. Rodríguez-Sánchez, P. Roy, R. Ruber, T.R. Saito, S. Schadmand, C. Scheidenberger, P. Schwarz, R. Sekiya, V. Serdyuk, M. Skurzok, B. Streicher, K. Suzuki, B. Szczepanczyk, X. Tang, N. Tortorelli, M. Vencelj, H. Wang, T. Weber, H. Weick, M. Will, K. Wimmer, A. Yamamoto, A. Yanai, J. Yoshida, J. Zhao
abstract
We have developed a new and unique experimental setup integrating the central part of the Wide Angle Shower Apparatus (WASA) into the Fragment Separator (FRS) at GSI. This combination opens up possibilities of new experiments with high-resolution spectroscopy at forward and measurements of light decay particles with nearly full solid-angle acceptance in coincidence. The first series of the WASA-FRS experiments have been successfully carried out in 2022. The developed experimental setup and two physics experiments performed in 2022 including the status of the preliminary data analysis are introduced.
Search for eta'-mesic nuclei using (p, d) reaction with FRS/Super-FRS at GSI/FAIR
Y. K. Tanaka, S. Bagchi, J. Benlliure, T. Dickel, V. Drozd, H. Ekawa, H. Fujioka, H. Geissel, F. Goldenbaum, C. Guo, E. Haettner, M. N. Harakeh, R.S. Hayano, S. Hirenzaki, C. Hornung, Y. Igarashi, N. Ikeno, K. Itahashi, M. Iwasaki, D. Jido, N. Kalantar-Nayestanaki, R. Kanungo, B. Kindler, R. Knöbel, D. Kostyleva, N. Kurz, N. Kuzminchuk, B. Lommel, Y. Ma, S. Y. Matsumoto, V. Metag, S. Minami, P. Moskal, I. Mukha, T. Nagae, H. Nagahiro, M. Nakagawa, H. J. Ong, H. Outa, S. Pietri, W. R. Plass, A. Prochazka, S. Purushothaman, C. Rappold, J. Ritman, J.L. Rodríguez-Sánchez, R. Ruber, O. Rundel, T. R. Saito, C. Scheidenberger, R. Sekiya, V. Serdyuk, H. Simon, B. Sitar, M. Skurzok, P. Strmen, B. Sun, I. Szarka, M. Takechi, I. Tanihata, S. Terashima, H. Weick, A. Yamamoto and J. Zhao
abstract
We plan a semi-exclusive measurement of the 12 C (p, dp) reaction to search for eta'-mesic nuclei, aiming at investigating in-medium properties of the eta'-meson. We employ a 2.5 GeV proton beam impinging on a carbon target to produce eta'-mesic 11 C nuclei via the 12 C (p, d) eta' 11 C reaction. Using coincidence measurements of the forward going deuterons, important for missing-mass spectroscopy, and decay protons emitted from the eta'-mesic nuclei. for event selection will provide a high experimental sensitivity to observe eta'-mesic nuclei. We will perform the measurements by combining the WASA detector system with the fragment separator FRS at GSI and also with the Super-FRS at FAIR in the future. The plan of the experiments and the present status are reported.
Analysis of the pd->pdpi0 Reaction Measured with WASA-at-COSY Facility in Order to Search for eta-mesic Helium
A. Khreptak, M. Skurzok, O. Rundel, P. Moskal
abstract
In this report, we briefly present the preliminary results of the search for 3He-eta bound system in pd->p d pi0 reaction.
Study of Three-Nucleon Dynamics in the dp breakup collisions using the WASA detector
P. Adlarson, ..., E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, I. Schätti-Ozerianska, M. Skurzok, M.J. Zieliński, et al.
abstract
Differential cross section for the 1H(d,pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of WASA detector at COSY-Juelich. The set of proton-proton coincidences registered at Forward Detector has been analysed on dense grid of kinematic variables, giving in total around 5600 data points. The cross section data are compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with three-nucleon force, Coulomb interaction or carried out in a relativistic regime.
Search for the exotic nuclear matter with WASA-at-COSY
P. Moskal
abstract
Search for the eta-mesic bound states with the WASA-at-COSY detector
M. Skurzok
abstract
The experiments dedicated to the search for eta-mesic Helium were performed with high statistics using WASA detection setups installed at the COSY accelerator in the Research Center Juelich. The search for the eta-mesic bound states is conducted via the measurement of the excitation function for selected decay channels of the He-eta systems using unique ramped beam technique. This report presents recent status of the data analysis.
Search for eta-mesic 3He in non-mesonic final state
O. Rundel, M. Skurzok and A. Khreptak
abstract
The experiment on searching for eta-mesic 3He nucleus was performed in May 2014 at COSY accelerator in Juelich by WASA-at-COSY Collaboration. The measurements were carried out using ramped beam technique which allows for the slow and continuous beam momentum change near the threshold of eta meson creation. The luminosity was obtained based on pd -> 3He? reaction and quasielastic proton-proton scattering. The bound state of eta-meson and 3He nucleus is searched for in pd -> 3He2gamma and pd -> 3He6gamma channels. The analysis is still in progress and the estimated upper limit value is on the level of few nanobarns.
Luminosity determination for the proton-deutron reactions using quasi-free reactions with WASA-at-COSY facility
A. Khreptak, O. Rundel and M. Skurzok
abstract
The scientific aim of our research is experimental confirmation of the existence of mesic-nucleus: a new exotic kind of nuclear matter consisting of nucleons and mesons. In this report we present the method of luminosity determination for experiment performed atWASA-at-COSY detector dedicated to search for 3He-eta bound state. This method is based on analysis of quasi-free reaction.
Luminosity determination for the proton-deuteron reaction using pd -> 3He eta channel with WASA-at-COSY detector
M. Skurzok, O. Rundel, A. Khreptak, P. Moskal
abstract
In this report one of the methods used for the luminosity determination for the experiment performed by WASA Collaboration to search for 3He-eta mesic nuclei is presented. The method is based on the analysis of pd -> 3He eta process.
Recent Results from WASA-at-COSY
H. Clement, P. Moskal, M. Skurzok
abstract
The detector system WASA-at-COSY has been operated at the Cooler Synchrotron COSY in the years from 2006 till 2015. In this article we report on recent results of the analyses of the meson production reactions in nucleon?nucleon, nucleon?deuteron, and deuteron?deuteron collisions with spin-polarized and unpolarized beams emphasizing the evidences for the existence of the dibaryon state in the proton-neutron system and the perspectives for the search of the eta-mesic helium.
Determination of the analysing power for the vec{p} p ->pp eta reaction using WASA-at-COSY detector system
P. Adlarson, ...,E. Czerwiński, O. Khreptak, W. Krzemień, P. Moskal, O. Rundel, M. Skurzok, M. Zieliński et al. (WASA-at-COSY Collaboration)
abstract
We report on the measurement of the analyzing power for the ~ pp -> pp eta reaction with beam
momenta of 2026 MeV/c and 2188 MeV/c performed with the WASA-at-COSY detector at the
Cooler Synchrotron COSY. The eta meson from the pp -> pp eta reaction was identified by the tech-
niques of missing mass and invariant mass. The angular distribution of the determined analyzing
power strongly disagrees with theoretical predictions. A comparison of the obtained A y angular
distribution with a series of associated Legendre polynomials revealed negligible contribution of
the Sd partial wave at Q = 15 MeV. However, at Q = 72 MeV, a significant interference of the Ps
and Pp partial waves was observed.
Searching for eta-mesic Helium with WASA-at-COSY facility
O. Rundel, O. Khreptak, M. Skurzok, W. Krzemien and P. Moskal
abstract
The search for the 4He-eta and 3He-eta bound states was performed with the WASA-at-COSY facility using a ramped beam technique in 2008, 2010 and 2014, respectively. The 2008 and 2010 data analyses has already been completed and resulted in the upper limits for the total cross sections for the eta-mesic 4He production in dd -> 3Henpi0 and dd -> 3Heppi- processes. No narrow structure which could be interpreted as a bound state was observed. The experiment carried out in 2014 collected the largest data sample for 3He-eta in the world. The data analysis is in progress. This article presents results of the 2010 data analysis and preliminary results of the 2014 data analysis.
Production and interaction of the eta meson with nucleons and nuclei
W. Krzemień, O. Khreptak, P. Moskal, I. Ozyrianska-Schaetti, O. Rundel, M. Skurzok and M. Zieliński
abstract
We report on the status of the search for eta-mesic nuclei and the studies of the interaction of the eta meson with nucleons. Recently we have completed the analysis of the new WASA-at-COSY data on the production of the eta meson with polarized proton beam. New results on the analyzing power for the p?p -> pp? reaction with more than an order of magnitude improved precision shed a new light on the production mechanism of the eta meson in nucleon-nucleon collisions. Also, the latest results of the search for eta-mesic nuclei are discussed.
Recent Results from WASA-at-COSY
H. Clement, P. Moskal, M. Skurzok
abstract
The detector system WASA-at-COSY has been operated at the Cooler Synchrotron COSY in the years from 2006 till 2015. In this article we report on recent results of the analyses of the meson production reactions in nucleon?nucleon, nucleon?deuteron, and deuteron?deuteron collisions with spin-polarized and unpolarized beams emphasizing the evidences for the existence of the dibaryon state in the proton-neutron system and the perspectives for the search of the eta-mesic helium.
Status and Perspectives of the Search for Eta-Mesic Nuclei
P. Moskal, M. Skurzok, W. Krzemień
abstract
In this report the search for eta-mesic nuclei is reviewed. The brief description ofeta-nucleus bound states for light nuclei like 4He and 3He.
Search for the eta-mesic Helium bound state with the WASA-at-COSY facility
M. Skurzok, W. Krzemien, O. Rundel, P. Moskal
abstract
We performed a search for 4He-eta bound state with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of eta-mesic nuclei is searched for in dd -> 3Henpi0 and dd -> 3Heppi- reactions by the measurement of the excitation functions in the vicinity of the {eta} production threshold. This paper presents the experimental method and the preliminary results of the data analysis for dd -> 3Henpi0 process.
Search for the 4He-eta bound state in dd->(4He-eta)_{bound}->3He n pi0 and dd->(4He-eta)_{bound}->3He p pi- reactions with the WASA-at-COSY facility
M. Skurzok , W. Krzemień, P. Moskal
abstract
In November 2010, the search for the 4He-{eta} bound state was per formed with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of eta - mesic nuclei is searched for in the measured excitation functions for the two reaction channels: dd ->3He n pi0 and dd ->3He p pi- near the eta production threshold. This report includes the description of the experimental method and the status of the data analysis.
Polarization determination for the studies of the eta meson production
I. Ozerianska, P. Moskal, M. Zieliński
abstract
The dynamics of ? meson production and the interaction of ? mesons with nucleons can be studied using the ?p p?pp? reaction via measurements of the analyzing power Ay. To this end, we have performed a measurement of the ?p p ?pp? reaction using the large acceptance and ? symmetric WASA-at-COSY detector, for beam momenta of 2026 MeV/c and 2188 MeV/c.
The eta-meson production with the polarized proton beam with WASA-at-COSY
I. Ozerianska, M. Hodana , P. Moskal
abstract
In November 2010, the azimuthal symmetric WASA detector and the polarized proton beam of COSY, have been used to collect a high statistics sample of (vec)p->ppeta reactions in order to determine the analyzing power as a function of the invariant mass spectra of the two particle subsystems. Here, we show studies of the infuence of the beam and target characteristics such as location and direction on the determination of the polarization.
Search for a dark photon with the WASA detector at COSY
Pawel Moskal for WASA at COSY Collaboration
abstract
49th Rencontres de Moriond QCD and High Energy Interactions
We present recent results on the search for the U boson based on the data collected by means of the WASA detector and the Cooler Synchrotron COSY.
Search for the eta-mesic 4He with WASA-at-COSY
W. Krzemien, P. Moskal, J. Smyrski and M. Skurzok
abstract
We conduct a search for the He ? ? bound state with the WASA-at-COSY facility measuring the excitation functions for the reaction channels: dd ? 3Hep?? and dd ? 3Hen?0, where the outgoing N ? ? pairs originate from the conversion of the ? meson on a nucleon inside the He nucleus. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Jülich with the WASA detector. The analysis of the 2008 data shows no signal of the 4He ? ? bound state. An upper limit for the cross-section for the bound state formation and decay in the process dd ? (4He ? ?)bound ? 3Hep??, was determined at the 90 % confidence level. In November 2010 a new data set was collected.
Search for the eta-mesic helium by means of WASA detector at COSY
P. Moskal, W. Krzemień, M. Skurzok
abstract
PoS Hadron2013 (2014) 163
The eta-mesic nuclei in which the eta meson is bound with nucleus via strong interaction was postulated about 25 years ago, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup and the Cooler Synchrotron COSY. The search is conducted via the measurement of the excitation function for the chosen decay channels of the 4He-eta system. Until now two reactions dd -> (4He-eta)bound ->3Heppi- and dd -> (4He-eta)bound ->3Henpi0 have been measured with the beam momentum varied continuously around the eta meson production threshold. This contribution includes description of recently published results of the WASA-at-COSY experiment as well as brief presentation of preliminary results from the analysis of new data sample with 20 times larger statistics.
Studies of Systematic Uncertainties of Polarization Estimation for Experiments with the WASA Detector at COSY
M. Hodana, P. Moskal, I. Ozerianska
abstract
In November 2010, the azimuthally symmetric WASA detector and the polarized proton beam of COSY have been used to collect a high statistics sample of ?p p ? pp? reactions in order to determine the analyzing power as a function of the invariant mass spectra of the two-particle subsystems. Here, we show studies of the influence of the beam and target characteristics such as location and direction on the determination of degree of the polarization.
Search for eta-mesic helium via deuteron-deuteron reactions with the WASA-at-COSY facility
M. Skurzok, P. Moskal, W. Krzemień
abstract
The eta-mesic nuclei in which the eta meson is bound with nucleus via strong interaction was postulated already in 1986, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup in the Forschungszentrum Julich. The search is conducted via the measurement of the excitation function for the chosen decay channels of the 4He-eta system. Untill now two reactions dd->(4He-eta)bs->3He p pi- and dd->(4He-eta)bs->3He n pi0 have been measured with the beam momentum ramped around the eta production threshold. This report includes the description of experimental method and status of the analysis.
Search for eta-mesic helium via the dd->(4He-eta)_bs -> 3He n pi 0 reaction with the WASA-at-COSY facility
M. Skurzok, W. Krzemień, P. Moskal
abstract
The existence of eta-mesic nuclei in which the $eta$ meson is bound in a nucleus by means of the strong interaction was postulated already in 1986 but it has not been yet confirmed experimentally. The discovery of this new kind of an exotic nuclear matter would be very important as it might allow for a better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium (4He-eta) is carried out with high statistics and high acceptance with the WASA detector, installed at the cooler synchrotron COSY of the Research Center Juelich. The search is conducted via the measurement of the excitation function for selected decay channels of the 4He-eta system. In the experiment, performed in November 2010, two reactions dd-->4He-eta-->3He p pi- and dd-->4He-eta-->3He n pi0 were measured with a beam momentum ramped from 2.127GeV/c to 2.422GeV/c. The proceedings will include description of the experimental method of the analysis.
Search for eta-mesic 4He with WASA-at-COSY detector.
W. Krzemień, P. Moskal, M. Skurzok, J. Smyrski
abstract
PoS Bormio2013 (2013) 036
Search for 4He-eta bound states with the WASA-at-COSY facility
M. Skurzok, W. Krzemien, P. Moskal
abstract
Test of charge conjugation invariance in the decay of the eta meson into pi(+)pi(-)pi(0)
M. Zieliński, P. Moskal
abstract
In this work we present the preliminary results of the analysis of the pp->pp
eta(->pp pi(+)pi(-)pi(0) reaction aiming to test the charge conjugation
symmetry C in strong interactions. Based on approximately $10^5$ identified
eta->pi(+)pi(-)pi(0) decay events we have extracted asymmetry parameters
sensitive to C symmetry violation for different isospin values of the final
state and we have established that all are consistent with zero within the
obtained accuracy.
Search for eta-mesic Helium with the WASA-at-COSY detector.
W. Krzemień, P. Moskal, J. Smyrski, M. Skurzok
abstract
A search for the 4He-eta bound state via exclusive measurement of the excitation function for the dd->3Heppi- reaction, was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta production in the dd -> 4He-eta reaction at 2.336 GeV/c. The corresponding excess energy in the 4He-eta system varied from -51.4 MeV to 22 MeV. The shape of the excitation function for the dd -> 3Heppi- was examined. No signal of the 4He-eta bound state was observed in the excitation function.
Study of the eta -> e+ e-gamma Decay Using WASA-at-COSY Detector System
M. Hodana, P. Moskal for the WASA - at - COSY Collaboration
abstract
At the turn of October and November 2008, the WASA-at-COSY collaboration performed an experiment to collect data on the eta meson decays in pd-->3He eta reactions. This report presents results of a study of the eta-->e+e-g conversion decay. The desired feature of this decay is that the final state e+e- pairs come from the conversion of a virtual gamma quantum and, therefore, they constitute a rich source of knowledge about the electromagnetic structure of decaying meson. This is a very important characteristic when it comes to study of a short-lived neutral particle like the eta meson, because the classical methods of particle scattering are not applicable here. The analysis performed on one third of the p-d data sample collected using the WASA-at-COSY detector, lead to the extraction of the eta transition form factor as a function of the e+e- mass and to the calculation of the slope parameter, related to the charge radius of the eta meson.
Search for the He-eta bound states with the WASA-at-COSY facility
M. Skurzok, W. Krzemień, P. Moskal
abstract
The existence of eta-mesic nuclei in which the $eta$ meson is bound in a nucleus by means of the strong interaction was postulated already in 1986 but it has not been yet confirmed experimentally. The discovery of this new kind of an exotic nuclear matter would be very important as it might allow for a better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium (4He-eta) is carried out with high statistics and high acceptance with the WASA detector, installed at the cooler synchrotron COSY of the Research Center Juelich. The search is conducted via the measurement of the excitation function for selected decay channels of the 4He-eta system. In the experiment, performed in November 2010, two reactions dd-->4He-eta-->3He p pi- and dd-->4He-eta-->3He n pi0 were measured with a beam momentum ramped from 2.127GeV/c to 2.422GeV/c. The poster will include description of the experimental method and status of the analysis.
Study of eta Meson Production with a Polarized Proton Beam
I. Ozerianska, P. Moskal, M. Hodana for the WASA-at-COSY Collaboration
abstract
Proceedings of the second International PrimeNet Workshop (2012) 87
These are the proceedings of the second PrimeNet Workshop, held in September 26-28, 2011, at the campus of Forschungszentrum J'{u}lich, Germany. This workshop is part of the activities in the project 'Study of Strongly Interacting Matter' (acronym HadronPhysics2), which is an integrating activity of the Seventh Framework Program of EU. This HP2 project contains several activities, one of them being the network PrimeNet having the focus on Meson Physics in Low-Energy QCD. This network is created to exchange information on experimental and theoretical ongoing activities on mainly eta and eta-prime physics at different European accelerator facilities and institutes.
Study of the eta --> e+ e- gamma decay
M. Hodana, P. Moskal for the WASA-at-COSY Collaboration
abstract
Proceedings of the second International PrimeNet Workshop (2012) 45
These are the proceedings of the second PrimeNet Workshop, held in September 26-28, 2011, at the campus of Forschungszentrum J'{u}lich, Germany. This workshop is part of the activities in the project 'Study of Strongly Interacting Matter' (acronym HadronPhysics2), which is an integrating activity of the Seventh Framework Program of EU. This HP2 project contains several activities, one of them being the network PrimeNet having the focus on Meson Physics in Low-Energy QCD. This network is created to exchange information on experimental and theoretical ongoing activities on mainly eta and eta-prime physics at different European accelerator facilities and institutes.
Search for eta-mesic 4He with WASA-at-COSY
W. Krzemień, P. Moskal, J. Smyrski for the WASA-at-COSY Collaboration
abstract
Proceedings of the second International PrimeNet Workshop (2012) 140
These are the proceedings of the second PrimeNet Workshop, held in September 26-28, 2011, at the campus of Forschungszentrum J'{u}lich, Germany. This workshop is part of the activities in the project 'Study of Strongly Interacting Matter' (acronym HadronPhysics2), which is an integrating activity of the Seventh Framework Program of EU. This HP2 project contains several activities, one of them being the network PrimeNet having the focus on Meson Physics in Low-Energy QCD. This network is created to exchange information on experimental and theoretical ongoing activities on mainly eta and eta-prime physics at different European accelerator facilities and institutes.
Search for the 4He-eta bound state with WASA-at-COSY
W. Krzemień
abstract
We conduct a search for the 4He-eta bound state with WASA-at-COSY facility, via a measurement
of the excitation functions for the dd ->3Heppi- reaction, where the outgoing p pi- pairs
originate from the conversion of the h meson on a nucleon inside the He nucleus. In June, 2008
first measurements of the excitation functions for the dd->3Heppi- reaction were performed. In
the experiment we used a slowly ramped COSY deuteron beam, scanning the range of momenta
corresponding to the variation of the excess energy for the 4He-eta system from -51.4 MeV to
22 MeV.
Study of the eta meson production with the polarised proton beam
P. Moskal, M. Hodana
abstract
The azimuthally symmetric WASA detector and the polarised proton beam of
COSY, enable investigations of energy and angular dependence of the beam analysing power
in the pp --> pp eta reaction. The aim of the studies is the determination of the partial wave
contributions via interference terms which are inaccessible from spin averaged observables. The
partial wave decomposition is mandatory for the understanding of the reaction dynamics and
for the determination of the ?-proton interaction, independently of the theoretical paradigm
used.
Search for eta-mesic helium using WASA-at-COSY.
P. Moskal
abstract
The installation of the WASA detector at the cooler synchrotron COSY opened the possibility to search for ??mesic helium with high statistics and high acceptance. A search for the 4He?? bound state is conducted via an exclusive measurement of the excitation function for the dd?3Hep?? reaction varying continuously the beam momentum around the threshold for the dd?4He? reaction. Ramping of the beam momentum and taking advantage of the large acceptance of the WASA detector allows to minimize systematical uncertainities.
Search for eta-mesic helium using the WASA-AT-COSY detector.
W. Krzemień, P. Moskal, J. Smyrski
abstract
Acta Phys. Polon. Supp. 2 (2009) 141-148
We conduct a search for the 4He-eta bound state with the WASA-at-COSY facility via the measurement of the excitation function for the reaction dd->3Heppi-. In first experiment performed in June 2008, we used COSY deuteron beam with a slowly ramped beam momentum corresponding to a variation of the excess energy for the 4He-eta system from -51.4 MeV to 22 MeV. Here we report on the status of the measurement and the data evaluation.
Studies of the eta meson decays with WASA
A. Kupsc, P. Adlarson, M. Berłowski, H. Bhatt, K. Chandwani, D. Coderre, M. Hodana, M. Janusz, Ch. Pauly, Ch. F. Redmer, N. Shah, J. Stepaniak, P. Vlasov, A. Winnemöller, J. Złomanczuk and L. Yurev
abstract
PoS CD09 (2009) 046
Studies of ? meson decays with the WASA detector are a major goal of the experimental program
at COSY-Juelich. In 2008 a sample of 107 eta mesons was collected in pd --> 3He eta reaction close to
threshold without trigger bias on the decay channels. The status of the analysis of various decay
channels is presented.
Multimeson production in pp interactions as a background for eta and eta' decays
A. Kupść, P. Moskal, M. Zieliński
abstract
Proceedings of MENU07 Conference (2008)
Multimeson production in pp interactions comprises important background for eta, omega and eta' mesons production experiments and for the studies of their decays planned with WASA detector at COSY. The available information about the reactions is summarized and the need for efforts to describe the processes is stressed.
Dynamics of the eta meson production in proton-proton collisions
M. Hodana, A. Kupść, P. Moskal
abstract
We briefly describe the present knowledge about the mechanism of the eta meson production in the collisions of nucleons. We stress the role of the spin degrees of freedom and discuss a possibility of investigations of the spin observables for the pp --> pp eta reaction using the WASA?at?COSY apparatus and the vertically polarized proton beam of COSY.
Search for the exotic nuclear matter with WASA-at-COSY
A. Khreptak, O. Rundel, M. Skurzok, P. Moskal
presented at: Przyszłość Fizyki Jądrowej Niskich Energii w Polsce a Rozwój Krajowej Infrastruktury Badawczej, 14-15.01.2019, Warsaw, Poland
Searching for eta-mesic 3He with WASA-at-COSY facility
O. Rundel, O. Khreptak, M. Skurzok, P. Moskal, W. Krzemień
presented at: 14th International Workshop on Meson Production (MESON 2016), 2-7 June 2016, Kraków
Study of the eta meson production with the polarized proton beam
I. Ozerianska, P.Moskal, M. Hodana
presented at: MesonNet 2013
Search for 4He-eta bound states in dd->3He p pi- and dd->3He n pi0 reactions with the WASA-at-COSY facility
Magdalena Skurzok, Wojciech Krzemien, Pawel Moskal
presented at: INPC 2013, Forence, Italy
Search for 4He-eta bound states in dd->3He p pi- and dd->3He n pi0 reactions with the WASA-at-COSY facility
M. Skurzok, W. Krzemien, P. Moskal
Monte Carlo studies of eta->4pi0 CP symmetry violating decay with WASA-at-COSY detector
T. Bednarski
presented at: MESON 2012 - International Workshop on Meson Production, Properties and Interaction, Kraków, Poland
Study of the eta --> e+e-gamma Decay using WASA-at-COSY Detector System
M. Hodana, P. Moskal
presented at: 12th International Workshop on Meson Production, Properties and Interaction, Kraków, Poland
Study of the eta-> pi+pi-pi0 decays in p-p interactions in view of the charge conjugation invariance
M. Zieliński
presented at: 12th International Workshop on Meson Production, Properties and Interaction KRAKÓW, POLAND 31 May - 5 June 2012
Search for He-eta bound states with the WASA-at-COSY facility
M. Skurzok, W. Krzemień, P. Moskal
presented at: MESON2012 - 12th International Workshop on Meson Production, Properties and Interaction
Study of the eta meson production with the polarized proton beam
I. Ozerianska, P.Moskal, M. Hodana
presented at: arXiv:1204.5509 [nucl-ex] ,PrimeNet Workshop
Measurement of the eta->pi+pi-pi0 decay with WASA-at-COSY in pd and pp interactions
P. Adlarson, M. Zielinski
presented at: MESON 2010 - International Workshop on Meson Production, Properties and Interaction, Kraków, Poland
