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.
On 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.
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 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.
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.
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.
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.
Isoscalar Single-Pion Production in the Region of Roper and d*(2380) Resonances
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 pn->pppi- and pp->pppi0 reactions 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=0.95-1.3 GeV (sgrt_s = 2.3 - 2.46 GeV), which includes the regions of Delta(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 Tp = 1 GeV. We observe a substantial increase of this cross section above 1 GeV, which can be related to the Roper resonance N?(1440), the strength of which shows up isolated from the Delta resonance in the isoscalar (Npi)I=0 invariant-mass spectrum. No evidence for a decay of the dibaryon resonance d*(2380) into the isoscalar (NNpi)I=0 channel is found. An upper limit of 180 mub (90 % C.L.) corresponding to a branching ratio of 9 % has been deduced.
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
Nucl. Phys. A 959, 102-115 (2017)
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 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.
J-PET detector system for studies of the electron-positron annihilations
M. Pawlik-Niedźwiecka, O. Khreptak, A. Gajos, A. Wieczorek, D. Alfs, T. Bednarski, P. Białas, C. Curceanu, E. Czerwiński, K. Dulski, B. Głowacz, N. Gupta-Sharma, M. Gorgol, B. C. Hiesmayr, B. Jasińska, D. Kamińska, G. Korcyl, P. Kowalski, W. Krzmień, N. Krawczyk, E. Kubicz, M. Mohammed, Sz. Niedźwiecki, L. Raczyński, Z. Rudy, M. Silarski, W. Wiślicki, B. Zgardzińska, M. Zieliński, and P. Moskal
abstract
Jagiellonian Positron Emission Tomograph (J-PET) has been recently constructed at the Jagiellonian University as a prototype of a cost-effective scanner for the metabolic imaging of the whole human body. J-PET detector is optimized for the measurement of momentum and polarization of photons from the electron-positron annihilations. It is built out of strips of plastic scintillators, forming three cylindrical layers. As detector of gamma quanta it will be used for studies of discrete symmetries and multiparticle entanglement of photons originating from the decays of ortho-positronium atoms.
Studies of discrete symmetries in a purely leptonic system using the Jagiellonian Positron Emission Tomograph
P. Moskal, D. Alfs, T. Bednarski, P. Białas, C. Curceanu, E. Czerwiński, K. Dulski, A. Gajos, B. Głowacz, N. Gupta-Sharma, M. Gorgol, B. C. Hiesmayr, B. Jasińska, D. Kamińska, O. Khreptak, G. Korcyl, P. Kowalski, W. Krzemień, N. Krawczyk, E. Kubicz, M. Mohammed, Sz. Niedźwiecki, M. Pawlik-Niedźwiecka, L. Raczyński, Z. Rudy, M. Silarski, J. Smyrski, A. Wieczorek, W. Wiślicki, B. Zgardzińska, and M. Zieliński
abstract
Discrete symmetries such as parity (P), charge-conjugation (C) and time reversal (T) are of fundamental importance in physics and cosmology. Breaking of charge conjugation symmetry (C) and its combination with parity (CP) constitute necessary conditions for the existence of the asymmetry between matter and antimatter in the observed Universe. The presently known sources of discrete symmetries violations can account for only a tiny fraction of the excess of matter over antimatter. So far CP and T symmetries violations were observed only for systems involving quarks and they were never reported for the purely leptonic objects. In this article we describe briefly an experimental proposal for the test of discrete symmetries in the decays of positronium atom which is made exclusively of leptons. The experiments are conducted by means of the Jagiellonian Positron Emission Tomograph (J-PET) which is constructed from strips of plastic scintillators enabling registration of photons from the positronium annihilation. J-PET tomograph together with the positronium target system enable to measure expectation values for the discrete symmetries odd operators constructed from (i) spin vector of the ortho-positronium atom, (ii) momentum vectors of photons originating from the decay of positronium, and (iii) linear polarization direction of annihilation photons. Linearly polarized positronium will be produced in the highly porous aerogel or polymer targets, exploiting longitudinally polarized positrons emitted by the sodium 22Na isotope. Information about the polarization vector of orthopositronium will be available on the event by event basis and will be reconstructed from the known position of the positron source and the reconstructed position of the orthopositronium annihilation. In 2016 the first tests and calibration runs are planned, and the
data collection with high statistics will commence in the year 2017.
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.
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.
