Marian Smoluchowski
Institute of Physics

Jagiellonian University in Kraków

Doctoral thesis

Study of the production mechanism of the eta meson in proton-proton collisions by means of analysing power measurements

Supervisor: prof. Paweł Moskal

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abstract

Defence year: 2006

HEP: arXiv:nucl-ex/0702010v1

The analysing power measurements for the p(pol)p -> pp eta reaction studied in this dissertation are used in the determination of the reaction mechanism of the eta meson production in nucleon-nucleon collisions. Measurements have been performed in the close-to-threshold energy region at beam momenta of p(beam)=2.010 and 2.085 GeV/c, corresponding to the excess energies of Q = 10 and 36 MeV, respectively. The experiments were realised by means of a cooler synchrotron and storage ring COSY along with a cluster jet target. For registration of the reaction products the COSY-11 facility has been used. The identification of the eta meson has been performed with the missing mass method. The results for the angular dependence of the analysing power combined with the hitherto determined isospin dependence of the total cross section for the $eta$ meson production in the nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11} resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of a pi meson between the colliding nucleons. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies.

Diploma thesis

Eta and Eta-prime meson production in the quasi-free proton-neutron collisions at the COSY–-11 facility

Supervisor: prof. Paweł Moskal

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abstract

Defence year: 2002

Both, the structure of the eta meson as well as its production mechanism are still under strong discussion and debate. The most possible hypothesis concerning the explanation of the almost three times larger mass for this meson observed experimentally relative to the theoretically calculated mass is a gluonium admixture to the eta-prime
wave function. This gluonium admixture should reflect itself in the production yield of the eta-prime
meson in proton-neutron collisions. Since the production of eta-prime
meson through the gluonium exchange is isospin independent, the ratio R(eta) = (pn->pn eta)/(pp->pp eta) close to threshold is expected to be R(eta-prime) = 1, after corrections for initial and final state interactions. The close to threshold eta-prime production in proton-proton collisions has already been investigated at the COSY-11 facility. Cross section values in the threshold region have been measured. However, until now no data have been taken for the eta-prime meson production in the proton-neutron collision. In order to investigate the eta-prime
production in proton-neutron collisions at the COSY synchrotron, the COSY-11 facility has been equipped with two new subsystems, namely the neutron detector and the spectator counter. The optimization of the topography for these additional detectors, the selection of the most suitable beam momentum and a discussion for the method of luminosity determination for the quasi-free pn->pn eta (eta-prime)
reactions are presented in this thesis. Rates for the production of eta and eta-prime
mesons in proton-neutron collisions at COSY-11 have been estimated. For the calculations a special fast program has been written.

Publications

ARTICLES CONFERENCE PROCEEDINGS POSTERS

1. Determination of the total width of the eta-prime meson
   E. Czerwiński, P. Moskal, D. Grzonka, R. Czyżykiewicz, D. Gil, B. Kamys, A. Khoukaz, J. Klaja, P. Klaja, W. Krzemień, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, P. Wüstner, J. Zdebik, M. Zieliński, W. Zipper
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   abstract

   Phys. Rev. Lett. 105, 122001 (2010)

   HEP: arXiv:1008.5294
   Taking advantage of both the low-emittance proton beam of the cooler synchrotron COSY and the high momentum precision of the COSY-11 detector system, the mass distribution of the eta-prime meson was measured with a resolution of 0.33??MeV/c2 (FWHM), improving the experimental mass resolution by almost an order of magnitude with respect to previous results. Based on the sample of more than 2300 reconstructed pp->pp eta-prime events, the total width of the eta-prime meson was determined to be Gamma(eta-prime) = 0.226+-0.017(stat)+-0.014(syst)??MeV/c2.
2. Two-proton correlation function for the pp -> pp + eta and pp to pp + pions reactions
   P. Klaja, P. Moskal, E. Czerwiński, R. Czyżykiewicz, A. Deloff, D. Gil, D. Grzonka, B. Kamys, A. Khoukaz, J. Klaja, W. Krzemień, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, J. Zdebik, M. Zieliński, W. Zipper
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   J. Phys. G: Nucl. Part. Phys. 37, 055003 (2010)

   HEP: arXiv:1003.4377
   For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. A two-proton correlation function was derived from the data for the pp -> ppX reaction, measured near the threshold of eta meson production. A technique developed for the purpose of this analysis permitted the correlation function to be established separately for the production of the pp + eta and of the pp + pions systems. The shape of the two-proton correlation function for pp-eta differs from that for pp(pions) and both do not show a peak structure, opposite to the results determined for inclusive measurements of heavy ion collisions.
3. Two-proton correlation function for the pp -> pp plus eta and pp -> pp plus pions reactions
   P. Klaja, P. Moskal, E. Czerwinski, R. Czyzykiewicz, A. Deloff, D. Gil, D. Grzonka, B. Kamys, A. Khoukaz, J. Klaja, W. Krzemien, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, J. Zdebik, M. Zielinski, W. Zipper
   abstract

   JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 37:5 055003 (2010)
   For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. A two-proton correlation function was derived from the data for the pp -> ppX reaction, measured near the threshold of eta meson production. A technique developed for the purpose of this analysis permitted the correlation function to be established separately for the production of the pp + eta and of the pp + pions systems. The shape of the two-proton correlation function for pp eta differs from that for pp(pions) and both do not show a peak structure, opposite to the results determined for inclusive measurements of heavy ion collisions.
4. Upper limit of the total cross section for the pn->pn eta-prime reaction
   J. Klaja, P. Moskal, S. D. Bass, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, T. Johansson, B. Kamys, A. Khoukaz, P. Klaja, W. Krzemień, W. Oelert, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, P. Wüstner, J. Zdebik, M. Zieliński, W. Zipper
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   Phys. Rev. C 81, 035209 (2010)

   HEP: arXiv:1003.4378
   The upper limit of the total cross section for the pn->pneta-prime reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R(eta-prime)=sigma(pn->pneta-prime)/sigma(pp->ppeta-prime) with the corresponding ratio for eta-meson production does not favor the dominance of the N*(1535) resonance in the production process of the eta-prime meson and suggests nonidentical production mechanisms for eta and eta-prime mesons.
5. Measurement of the invariant mass distributions fot he pp->pp eta-prime reaction at excess energy of Q = 16.4 MeV
   P. Klaja, P. Moskal, E. Czerwiński, R. Czyżykiewicz, A. Deloff, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, K. Nakayama, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, J. Zdebik, M. Zieliński, W. Zipper
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   Phys. Lett. B 684:11-16 (2010)

   HEP: arXiv:1001.5174
   The proton?proton and proton? invariant mass distributions have been determined for the reaction at an excess energy of . The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the reaction and reveal an enhancement for large relative proton?proton momenta. This result, together with the fact that the proton?? interaction is much stronger that the proton? interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.
6. Upper limit of the total cross section for the pn -> pn eta ' reaction
   J. Klaja, P. Moskal, SD. Bass, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, T. Johansson, B. Kamys, A. Khoukaz, P. Klaja, W. Krzemien, W. Oelert, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, M. Zielinski, W. Zipper
   abstract

   PHYSICAL REVIEW C 81:3 035209 (2010)
   The upper limit of the total cross section for the pn -> pn eta' reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R-eta' = sigma(pn -> pn eta')/sigma(pp -> pp eta') with the corresponding ratio for eta-meson production does not favor the dominance of the N*(1535) resonance in the production process of the eta' meson and suggests nonidentical production mechanisms for eta and eta' mesons.
7. Measurement of the invariant mass distributions for the pp -> pp eta ' reaction at excess energy of Q=16.4 MeV
   P. Klaja, P. Moskal, E. Czerwinski, R. Czyzykiewicz, A. Deloff, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, K. Nakayama, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, J. Zdebik, M. Zielinski, W. Zipper
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   PHYSICS LETTERS B 684:1 p. 11-16 (2010)
   The proton-proton and proton-eta' invariant mass distributions have been determined for the pp -> pp eta' reaction at an excess energy of Q = 16.4 MeV. The measurement was carried Out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp -> pp eta reaction and reveal an enhancement for large relative proton-proton momenta. This result, together with the fact that the proton-eta interaction is Much stronger that the proton-eta' interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson. (C) 2010 Elsevier B.V. All rights reserved.
8. Invariant-mass distributions for the pp -> pp eta reaction at Q=10 MeV
   P. Moskal, R. Czyzykiewicz, E. Czerwinski, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, P. Klaja, W. Krzemien, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, MJ. Zielinski, W. Zipper
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   EUROPEAN PHYSICAL JOURNAL A 43:2 p. 131-136 (2010)
   Proton-proton and proton-eta invariant-mass distributions and the total cross-section for the pp -> pp eta reaction have been determined near the threshold at an excess energy of Q = 10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant-mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q = 15.5 MeV and Q = 40 MeV.
9. Invariant mass distributions for the pp->pp eta reaction at Q = 10 MeV
   P. Moskal, R. Czyżykiewicz, E. Czerwiński, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, P. Klaja, W. Krzemień, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, M. Zieliński, W. Zipper
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   abstract

   Eur. Phys. J. A 43:131-136 (2010)

   HEP: arXiv:0912.1592
   Proton-proton and proton-eta invariant-mass distributions and the total cross-section for the pp -> pp h reaction have been determined near the threshold at an excess energy of Q = 10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant-mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q = 15.5 MeV and Q = 40 MeV.
10. Generalized Dalitz plot analysis of the near-threshold pp -> ppK(+)K(-) reaction in view of the K+K- final state interaction
    M. Silarski, P. Moskal, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, P. Klaja, W. Krzemien, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, M. Zielinski, W. Zipper, J. Zdebik
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    PHYSICAL REVIEW C 80:4 045202 (2009)
    The excitation function for the pp -> ppK(+)K(-) reaction revealed a significant enhancement close to threshold that may plausibly be assigned to the influence of the pK(-) and K+K- final-state interactions. In an improved reanalysis of COSY-11 data for the pp -> ppK(+)K(-) reaction at excess energies of Q = 10 and 28 MeV, including the proton-K- interaction, the enhancement is confirmed. Invariant mass distributions for the two- and three-particle subsystems allow us to test at low excess energies the ansatz and parameters for the description of the interaction in the ppK(+)K(-) system as derived from the COSY-ANKE data. Finally, based for the first time on the low-energy K+K- invariant mass distributions and the generalized Dalitz plot analysis, we estimate the scattering length for the K+K- interaction to be vertical bar Re(a(K+K-))vertical bar = 0.5(-0.5)(+4.0) fm and Im(a(K+K-)) = 3.0 +/- 3.0 fm.
11. Generalized Dalitz plot analysis of the near-threshold pp->ppK+K- reaction in view of the K+K- final state interaction
    M. Silarski, P. Moskal, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, J. Klaja, P. Klaja, W. Krzemień, W. Oelert, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Täschner, P. Winter, M. Wolke, P. Wüstner, M. Zieliński, W. Zipper, J. Zdebik
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    abstract

    Phys. Rev. C 80, 045202 (2009)

    HEP: arXiv:0909.3974
    The excitation function for the pp->ppK+K- reaction revealed a significant enhancement close to threshold which may plausibly be assigned to the influence of the pK- and K+K- final state interactions. In an improved reanalysis of COSY-11 data for the pp-> ppK+K- reaction at excess energies of Q = 10 MeV and 28 MeV including the proton-K- interaction the enhancement is confirmed. Invariant mass distributions for the two- and three-particle subsystems allow to test at low excess energies the ansatz and parameters for the description of the interaction in the ppK+K- system as derived from the COSY-ANKE data. Finally, based for the first time on the low energy K+K- invariant mass distributions and the generalized Dalitz plot analysis, we estimate the scattering length for the K+K- interaction to be |Re(a_K+K-)| = 0.5 + 4.0 -0.5 fm and Im(a_K+K-) = 3.0 +- 3.0 fm.
12. 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.
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    Phys. Lett. B 677:24-29 (2009)

    HEP: arXiv:0811.2763
    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.
13. Measurement of the eta -> 3 pi(0) Dalitz plot distribution with the WASA detector at COSY
    C. Adolph, M. Angelstein, M. Bashkanov, U. Bechstedt, S. Belostotski, M. Berlowski, H. Bhatt, J. Bisplinghoff, A. Bondar, B. Borasoy, M. Buscher, H. Calen, K. Chandwani, H. Clement, E. Czerwinski, R. Czyzykiewicz, G. D'Orsaneo, D. Duniec, C. Ekstrom, R. Engels, W. Erven, W. Eyrich, P. Fedorets, O. Felden, K. Fransson, D. Gil, F. Goldenbaum, K. Grigoryev, A. Heczko, C. Hanhart, V. Hejny, F. Hinterberger, M. Hodana, B. Hoistad, A. Izotov, M. Jacewicz, M. Janusz, BR. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, I. Keshelashvili, O. Khakimova, A. Khoukaz, K. Kilian, N. Kimura, S. Kistryn, J. Klaja, P. Klaja, H. Kleines, B. Klos, A. Kowalczyk, F. Kren, W. Krzemien, P. Kulessa, S. Kullander, A. Kupsc, A. Kuzmin, V. Kyryanchuk, J. Majewski, H. Machner, A. Magiera, R. Maier, R. Marciniewski, W. Migdal, UG. Meissner, et al.
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    PHYSICS LETTERS B 677:1-2 p. 24-29 (2009)
    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 pious was Studied using 1.2 x 10(5) fully reconstructed events. and the quadratic slope parameter alpha was determined to be -0.027 +/- 0.008(stat) +/- 0.005(syst). The result is consistent with previous measurements and further corroborates the importance of pion-pion final state interactions. (C) 2009 Elsevier B.V. All rights reserved.
14. Near-threshold production of the eta meson via the quasi-free pn->pneta reaction
    P. Moskal, R. Czyżykiewicz, H.-H. Adam, S. D. Bass, A. Budzanowski, E. Czerwiński, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, T. Johansson, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taeschner, M. Wolke, P. Wuestner, M. Zieliński, W. Zipper, J. Zdebik
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    Phys. Rev. C 79, 015208 (2009)

    HEP: arXiv:0807.0722
    Total cross sections for the quasifree pn->pn? reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding cross sections for the pp?pp? reaction by a factor of about 3 in contrast to the factor of 6 established for higher excess energies. To large extent, the observed decrease of the ratio sigma(pn->pn?)/sigma(pp->pp?) toward threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final-state interactions. The experiment was conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton-neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn?pn? reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.
15. Isospin dependence of the eta-prime meson production in nucleon-nucleon collisions.
    J. Przerwa, P. Moskal, A. Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, L. Jarczyk, T. Johansson, B. Kamys, A. Khoukaz, P. Klaja, W. Krzemień, W. Oelert, C. Piskor-Ignatowicz, J. Ritman, B. Rejdych, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, M. Zieliński, W. Zipper
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    abstract

    Int.J.Mod.Phys. A24 (2009) 458-461

    HEP: arXiv:0810.1406
    A comparison of the close-to-threshold total cross section for the eta prime production in pp -> pp eta prime and pn -> pn eta prime reactions constitutes a tool to investigate the eta prime meson structure and the reaction mechanism in the channels of isospin I=0 and I=1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta prime meson. In this contribution we present preliminary results of measurement of the quasi-free production of the eta prime meson in the proton-neutron collisions conducted using the COSY-11 facility.
16. ISOSPIN DEPENDENCE OF THE eta ' MESON PRODUCTION IN NUCLEON-NUCLEON COLLISIONS
    J. Przerwa, P. Moskal, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, L. Jarczyk, T. Johansson, B. Kamys, A. Khoukaz, P. Klaja, W. Krzemien, W. Oelert, C. Piskor-Ignatowicz, J. Ritman, B. Rejdych, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, MJ. Zielinski, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 24:2-3 p. 458-461 (2009)
    A comparison of the close-to-threshold total cross section for the eta' production in pp -> pp eta' and pn -> pn eta' reactions constitutes a tool to investigate the eta' meson structure and the reaction mechanism in the channels of isospin I = 0 and I = 1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta' meson. In this contribution we present preliminary results of measurement of the quasifree production of the eta' meson in the proton-neutron collisions conducted using the COSY-11 facility.
17. SEARCH FOR THE He-3-eta BOUND STATE AT COSY-11
    W. Krzemien, J. Smyrski, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, W. Oelert, J. Przerwa, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, A. Taschner, M. Wolke, P. Wustner, J. Zdebik, MJ. Zielinski, W. Zipper
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    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 24:2-3 p. 576-580 (2009)
    We have measured excitation function for dp -> ppp pi(-) reaction near the. production threshold. We observe an enhancement of the counting rate above the threshold which can originate from the production of the. meson in the reaction dp -> He-3 eta and its subsequent absorption on neutron in the 3He nucleus leading to creation of the p pi(-) pair.
18. Search for the 3He-eta bound state at COSY-11.
    W. Krzemien, J. Smyrski, A. Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, W. Oelert, J. Przerwa, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, A. Taeschner, M. Wolke, P. Wuestner, J. Zdebik, M. Zieliński, W. Zipper
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    abstract

    Int.J.Mod.Phys. A24 (2009) 576-580

    HEP: arXiv:0810.2330
    We have measured excitation function for dp -> ppp_pi- reaction near the eta production threshold. We observe an enhancement of the counting rate above the threshold which can originate from the production of the eta meson in the reaction dp -> 3He eta and its subsequent absorption on neutron in the 3He nucleus leading to creation of the p_pi- pair.
19. Near-threshold production of the eta meson via the quasifree pn -> pn eta reaction
    P. Moskal, R. Czyzykiewicz, HH. Adam, SD. Bass, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, T. Johansson, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Wustner, M. Zielinski, W. Zipper, J. Zdebik
    abstract

    PHYSICAL REVIEW C 79:1 015208 (2009)
    Total cross sections for the quasifree pn -> pn eta reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding cross sections for the pn -> pn eta reaction by a factor of about 3 in contrast to the factor of 6 established for higher excess energies. To large extent, the observed decrease of the ratio s(pn -> pn eta)/s=sigma(pn -> pn eta) toward threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final-state interactions. The experiment was conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton- neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn -> pn eta reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.
20. Near threshold production of the pseudoscalar mesons at the COSY-11 facility
    P. Moskal, R. Czyzykiewicz, HH. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, X. Kilian, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, M. Wolke, P. Winter, P. Wustner, M. Zielinski, W. Zipper
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    PROC. PROCEEDINGS OF THE 11TH WORKSHOP ON THE PHYSICS OF EXCITED NUCLEONS p. 202-+ (2008)
    We summarise measurements of the COSY-11 collaboration concerning the excitation functions of the near threshold pseudoscalar meson production in the proton-proton interaction. The results are discussed in the context of the meson-nucleon and hyperon-nucleon interactions. We conclude that the eta-proton interaction is significantly stronger than the eta'-proton interaction. Similarly, we found that the hyperon Lambda interacts with the nucleon considerably stronger than the hyperon Sigma, and that the interaction of K--proton is much stronger than this of the K+-proton.
21. Dynamics of the near threshold eta meson production in proton-proton interaction
    R. Czyzykiewicz, P. MoSkal, HH. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Hodana, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, B. Lorentz, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Taschner, K. Ulbrich, P. Winter, M. Wolke, P. Wustner, M. Zielinski, W. Zipper
    abstract

    PROC. PROCEEDINGS OF THE 11TH WORKSHOP ON THE PHYSICS OF EXCITED NUCLEONS p. 219-+ (2008)
    We present the results of measurements of the analysing power for the pp -> pp eta reaction at the excess energies of Q = 10 and 36 MeV, and interpret these results within the framework of the meson exchange models. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in s-wave.
22. Study of the He-3-eta system in d-p collisions
    J. Smyrski, HH. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, A. Siemaszko, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. NUCLEAR PHYSICS A 790 p. 438C-441C (2007)
    We have measured excitation functions for the dp -> He-3 X, (X = pi(0),eta) channels near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The excitation function for the reaction dp -> He-3 pi(0) does not show any structure which could originate from the decay of He-3 - eta bound state. We measured also the threshold excitation curve for the dp -> He-3 X process, however, contrary to the SATURNE results, we observe no cusp near the eta threshold.
23. Measurement of the dp -> He-3 eta reaction near threshold
    J. Smyrski, HH. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, T. Mersmann, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PHYSICS LETTERS B 649:4 p. 258-262 (2007)
    Total and differential cross sections for the dp -> He-3 eta reaction have been measured near threshold for He-3 center-of-mass momenta in the range from 17.1 MeV/c to 87.5 MeV/c. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target detecting the He-3 ejectiles with the COSY-11 facility. The forward-backward asymmetries of the differential cross sections deviate clearly from zero for center-of-mass momenta above 50 MeV/c indicating the presence of higher partial waves in the final state. Below 50 MeV/c center-of-mass momenta a fit of the final state enhancement factor to the data of the total cross sections results in the He-3-eta scattering length of vertical bar a vertical bar = 4.3 +/- 0.5fm. (C) 2007 Elsevier B.V. All rights reserved.
24. Mechanism of near-threshold production of the eta meson
    R. Czyzykiewicz, P. Moskal, HH. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Hodana, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, B. Lorentz, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, K. Ulbrich, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PHYSICAL REVIEW LETTERS 98:12 122003 (2007)
    Measurements of the analyzing power for the pp -> pp eta reaction have been performed at excess energies of Q=10 and 36 MeV. The determined analyzing power is essentially consistent with zero, implying dominance of the s wave at both excess energies. The angular dependence of the analyzing power, combined with the isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal that the excitation of the nucleon to the S-11(1535) resonance is predominantly due to the exchange of the pi meson between the colliding nucleons.
25. Eta and eta-prime mesons production at COSY-11.
    P. Moskal, H.-H. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, B. Rejdych, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Int. J. Mod. Phys. A22:305-316  (2007)

    HEP: arXiv:hep-ex/0609035
    The low emittance and small momentum spread of the proton and deuteron beams of the Cooler Synchrotron COSY combined with the high mass resolution of the COSY-11 detection system permit to study the creation of mesons in the nucleon-nucleon interaction down to the fraction of MeV with respect to the kinematical threshold. At such small excess energies, the ejectiles possess low relative momenta and are predominantly produced with the relative angular momentum equal to zero. Taking advantage of these conditions we have performed investigations aiming to determine the mechanism of the production of eta and eta' mesons in the collision of hadrons as well as the hadronic interaction of these mesons with nucleons and nuclei. In this proceedings we address the ongoing studies of the spin and isospin dependence for the production of the eta and eta' mesons in free and quasi-free nucleon-nucleon collisions. New results on the spin observables for the vec(p)p --> pp eta reaction, combined with the previously determined total cross section isospin dependence, reveal a statistically significant indication that the excitation of the nucleon to the S11(1535) resonance, the process which intermediates the production of the eta meson in the nucleon-nucleon interactions, is predominantly due to the exchange of the pi meson between the colliding nucleons.
26. General thoughts to the Kaon pair production in the threshold region.
    W. Oelert, H.-H. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
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    abstract

    Int. J. Mod. Phys. A22: 502-504 (2007)

    HEP: arXiv:hep-ph/0609092
    Simple--minded thoughts about the cross sections for the reactions pp-->ppK+K- and pp-->ppK0K0 are presented, which certainly do not account for the complex coupled channel problem but rather provide some ideas into the mutual reaction dynamics.
27. Study of the production mechanism of the eta meson by means of analysing power measurements.
    R. Czyżykiewicz, P. Moskal, H.-H. Adam, A. Budzanowski, E. Czerwiński, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, B. Lorentz, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, H. Rohdjess, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, K. Ulbrich, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Int. J. Mod. Phys. A22:518-522 (2007)

    HEP: arXiv:nucl-ex/0608036
    Information about the production mechanism of the eta meson in proton-proton collisions can be inferred by confronting the experimental studies on the analysing power for the p(pol)p --> pp eta reaction with the theoretical predictions of this observable. Results show that the predictions of pure pseudoscalar- or vector meson exchange model are insufficient to describe the analysing powers.
28. Near threshold eta meson production in dp collisions.
    C. Piskor-Ignatowicz, J. Smyrski, P. Moskal, H.-H. Adam, A. Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, J. Majewski, W. Oelert, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Int. J. Mod. Phys. A22: 528-532 (2007)

    HEP: arXiv:hep-ex/0611042
    Preliminary results of recent measurements of the near threshold eta meson production in the dp-->dp eta reaction are presented. The experiment was performed at the COSY-Juelich accelerator with the use of the COSY-11 detection system. Data were taken for three values of deuteron beam momenta corresponding to excess energies of 3.2, 6.1 and 9.2 MeV. The energy dependence of the total cross section confirms a strong effect of the final state interaction.
29. General thoughts to the kaon pair production in the threshold region
    W. Oelert, HH. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 22:2-3 p. 502-504 (2007)
    Simple-minded thoughts about the cross sections for the reactions pp -> ppK(+)K(-) and pp. ppK(0)K(0) are presented, which certainly do not account for the complex coupled channel problem but rather provide some ideas into the mutual reaction dynamics.
30. Study of the production mechanism of the eta meson by means of analysing power measurements
    R. Czyzykiewicz, P. Moskal, HH. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, B. Lorentz, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, H. Rohdjess, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, K. Ulbrich, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 22:2-3 p. 518-522 (2007)
    Information about the production mechanism of the eta meson in proton-proton collisions can be inferred by confronting the experimental studies on the analysing power for the (p) over right arrowp -> pp eta reaction with the theoretical predictions of this observable. The determined analysing powers for Q=10 MeV and Q=36 MeV are consistent with zero. Results show that the predictions of pure pseudoscalar meson exchange model fairly describe the experimental data, while the predictions of pure vector meson exchange dominance model disagree with the data at the level of 4.3 sigma.
31. Near threshold eta meson production in dp collisions
    C. Piskor-Ignatowicz, J. Smyrski, P. Moskal, HH. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, J. Majewski, W. Oelert, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 22:2-3 p. 528-532 (2007)
    Preliminary results of recent measurements of the near threshold. meson production in the dp -> dp eta reaction are presented. The experiment was performed at the COSY-Juelich accelerator with the use of the COSY-11 detection system. Data were taken for three values of deuteron beam momenta corresponding to excess energies of 3.2, 6.1 and 9.2 MeV. The energy dependence of the total cross section con. rms a strong e. ect of the. nal state interaction.
32. Study of the low energy interaction of hadrons at COSY-11
    P. Moskal, R. Czyżykiewicz, E. Czerwiński, D. Grzonka, A. Budzanowski, D. Gil, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, P. Wüstner, M. Zieliński, W. Zipper
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    abstract

    Frascati Phys. Ser. XLVI:1137 (2007)
    We summarize the studies of the low energy hadronic interaction of the KK and pK system performed by the COSY-11 collaboration. We discuss also the question of the existence of the ??3He bound state in the context of the experiments conducted by means of the COSY-11 facility
33. Measurement of the dp -> He-3 eta reaction near threshold.
    J. Smyrski, H.-H. Adam, A. Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, T. Mersmann, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Phys .Lett. B649: 258 (2007)

    HEP: arXiv:nucl-ex/0702043
    Total and differential cross sections for the dp --> 3He eta reaction have been measured near threshold for 3He center-of-mass momenta in the range from 17.1 MeV/c to 87.5 MeV/c. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target detecting the 3He ejectiles with the COSY-11 facility. The forward-backward asymmetries of the differential cross sections deviate clearly from zero for center-of-mass momenta above 50 MeV/c indicating the presence of higher partial waves in the final state. Below 50 MeV/c center-of-mass momenta a fit of the final state enhancement factor to the data of the total cross sections results in the 3He eta scattering length of a = |2.9 +/- 0.6| + i (3.2 +/- 0.4) fm.
34. Direct measurement of the total width of the eta prime meson
    E. Czerwiński, P. Moskal, D. Grzonka, A. Budzanowski, R. Czyżykiewiczy, D. Gil, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, M. Wolke, P. Wüstner, M. Zieliński, W. Zipper
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    abstract

    Frascati Phys. Ser. XLVI:489 (2007)
    Using stochastically cooled proton beam of the cooler synchrotron COSY and the COSY-11 apparatus we have measured the mass distribution of the eta prime meson producing it via the pp->ppeta' reaction. The preliminary analysis shows that the achieved experimental mass resolution amounts to about 0.3 MeV (FWHM). Such precision with about 2300 events gathered at five excess energies should permit for the extraction of the width of the eta' meson with an accuracy of about 10 keV. In this article we describe the method of the mea-surement and present preliminary results.
35. Hadronic He-3 eta production near threshold.
    H.-H. Adam, I. Geck, A. Khoukaz, T. Lister, R. Santo, S. Steltenkamp, A. Täschner, E. Czerwiński, R. Czyżykiewicz, M. Janusz, L. Jarczyk, B. Kamys, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, J. Smyrski, D. Grzonka, K. Kilian, W. Oelert, T. Sefzick, P. Winter, M. Wolke, P. Wüstner, A. Budzanowski, T. Rożek, M. Siemaszko, W. Zipper
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    abstract

    Phys.Rev. C75 014004 (2007)
    Measurements of ? meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY (Jülich). Results on total and differential cross sections for the pd?3He? reaction are presented at five excess energies between Q=5.0 and Q=40.6 MeV. The angular distributions show a transition from an almost isotropic emission close to threshold to a highly anisotropic distribution at higher excess energies. The total cross sections reveal a strong ?-3He final state interaction, corresponding to a scattering length of |?(a)|=(4.2?0.5) fm and ?(a)=(0.4?1.9) fm
36. Study of the He-3 eta system in d p collisions.
    J. Smyrski, H.-H. Adam, A.Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Nucl. Phys. A790:438 (2007)

    HEP: arXiv:nucl-ex/0612009
    We have measured excitation functions for the d+p->3He+X, (X=pi0, eta) channels near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The excitation function for the reaction d+p->3He+pi0 does not show any structure which could originate from the decay of 3He-eta bound state. We measured also the threshold excitation curve for the d+p->3He+X process, however, contrary to the SATURNE results, we observe no cusp near the eta threshold.
37. Mechanism of the close-to-threshold production of the eta meson.
    R. Czyzykiewicz, P. Moskal, H. -H. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Hodana, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, B. Lorentz, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, K. Ulbrich, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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    abstract

    Phys. Rev. Lett. 98: 122003 (2007)

    HEP: arXiv:hep-ex/0611015
    Measurements of the analysing power for the p(pol)p --> ppeta reaction have been performed in the close-to-threshold energy region at beam momenta of p_{beam}=2.010 and 2.085 GeV/c, corresponding to excess energies of Q=10 and 36 MeV, respectively. The determined analysing power is essentially consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies. The angular dependence of the analysing power, combined with the hitherto determined isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11}(1535) resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of the pi meson between the colliding nucleons.
38. Hadronic He-3 eta production near threshold
    HH. Adam, I. Geck, A. Khoukaz, T. Lister, R. Santo, S. Steltenkamp, A. Taschner, E. Czerwimski, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, J. Smyrski, D. Grzonka, K. Kilian, W. Oelert, T. Sefzick, P. Winter, M. Wolke, P. Wustner
    abstract

    PHYSICAL REVIEW C 75:1 014004 (2007)
    Measurements of eta meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY (Julich). Results on total and differential cross sections for the pd -> He-3 eta reaction are presented at five excess energies between Q=5.0 and Q=40.6 MeV. The angular distributions show a transition from an almost isotropic emission close to threshold to a highly anisotropic distribution at higher excess energies. The total cross sections reveal a strong eta-He-3 final state interaction, corresponding to a scattering length of vertical bar(a)vertical bar=(4.2 +/- 0.5) fm and (a)=(0.4 +/- 1.9) fm.
39. Threshold hyperon production in proton-proton collisions at COSY-11
    T. Rozek, D. Grzonka, HH. Adam, A. Budzanowski, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Kowina, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, Z. Zhang, W. Zipper
    abstract

    PHYSICS LETTERS B 643:5 p. 251-256 (2006)
    The Sigma(+) hyperon production was measured at the COSY-11 spectrometer via the pp -> nK(+)Sigma(+) reaction at excess energies of Q = 13 MeV and Q = 60 MeV. These measurements continue systematic hyperon production studies via the pp -> pK(+)Lambda/Sigma(0) reactions where a strong decrease of the cross section ratio close-to-threshold was observed. In order to verify models developed for the description of the Lambda and Sigma(0) production we have performed the measurement on the Sigma(+) hyperon and found unexpectedly that the total cross section is by more than one order of magnitude larger than predicted by all anticipated models. After the reconstruction of the kaon and neutron four momenta, the Sigma(+) is identified via the missing mass technique. Details of the method and the measurement will be given and discussed in view of theoretical models. (c) 2006 Elsevier B.V. All rights reserved.
40. Study of the He-3-eta system in d-p collisions at COSY-11
    J. Smyrski, HH. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, A. Heczko, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, J. Majewski, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, A. Taschner, P. Winter, M. Wolke, P. Wustner, Z. Zhang, W. Zipper
    abstract

    PROC. ACTA PHYSICA SLOVACA 56:3 p. 213-219 (2006)
    We present preliminary results from dp -> He-3 X, (X = pi(0),eta) measurements near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The He-3 ejectiles were registered with the COSY-11 detection setup. The ongoing data analysis should deliver high precision data for the dp -> He-3 eta total and differential cross sections for the excess energies in the range from threshold up to 9 MeV. The preliminary excitation function for the reaction dp -> 3 He pi(0) does not show any structure which Could originate from the decay of He-3 - eta bound state. We present also a threshold excitation curve for the dp - He-3 X channel. Contrary to corresponding results from SATURNE we see no cusp in the vicinity of the eta threshold.
41. The analyzing power for the (p)over-right-arrowp -> pp eta reaction at Q=10 MeV
    R. Czyzykiewicz, P. Moskal, HH. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, B. Lorentz, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, H. Rohdjess, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, K. Ulbrich, P. Winter, M. Wolke, P. Wustner, Z. Zhang, W. Zipper
    abstract

    PROC. ACTA PHYSICA SLOVACA 56:3 p. 387-396 (2006)
    The analyzing power A(y) for the (p) over right arrowp -> pp eta reaction has been determined at the beam momentum p(beam) = 2010 MeV/c, corresponding to the excess energy Q = 10 MeV. In the paper the method of the data analysis is briefly presented.
42. The Analysing power for the polarized-p p ---> p p eta reaction at Q=10-MeV.
    R. Czyzykiewicz, P. Moskal, H.-H. Adam, A. Budzanowski, E. Czerwinski, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, B. Lorentz, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, H. Rohdjess, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, K. Ulbrich, P. Winter, M. Wolke, P. Wuestner, Z. Zhang, W. Zipper
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    abstract

    Acta Phys. Slov. 56:387-396  (2006)

    HEP: arXiv:nucl-ex/0603018
    The analyzing power A_y for the p(pol)p --> pp eta reaction has been determined at the beam momentum p_{beam}=2010 MeV/c, corresponding to the excess energy Q=10 MeV. In the paper the method of the data analysis is briefly presented.
43. Study of the He-3 - eta system in d-p collisions at COSY-11.
    J. Smyrski, H.-H. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, A. Heczko, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, J. Majewski, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, Z. Zhang, W. Zipper
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    abstract

    Acta Phys. Slov. 56, 213 (2006)

    HEP: arXiv:nucl-ex/0603023
    We present preliminary results from dp --> 3He X (X=pi0,eta) measurements near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The 3He ejectiles were registered with the COSY-11 detection setup. The ongoing data analysis should deliver high precision data for the dp --> 3He eta total and differential cross sections for the excess energies in the range from threshold up to 9 MeV. The preliminary excitation function for the reaction dp --> 3He pi0 does not show any structure which could originate from the decay of 3He-eta bound state. We present also a threshold excitation curve for the dp --> 3He X channel. Contrary to corresponding results from SATURNE we see no cusp in the vicinity of the eta threshold.
44. Correlation femtoscopy for studying eta meson production mechanism.
    P. Klaja, P. Moskal, H.-H. Adam, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, J. Majewski, W. Migdal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, P. Winter, M. Wolke, P. Wuestner, Z. Zhang, W. Zipper
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    abstract

    Acta Phys. Slov. 56 (2006) 251-259

    HEP: arXiv:nucl-ex/0603025
    The high statistics data from the pp -> ppeta reaction measurement, delivered by the COSY-11 collaboration, are now being evaluated using the correlation femtoscopy technique. This method is based on the relative momentum correlations of two emitted protons and may permit determination of the size of the reaction volume. For the very first time, we apply an intensity interferometry technique to study the mechanism of the meson production via the nucleon-nucleon interaction close to the kinematical threshold. We invented a method to determine correlation function for the ppeta system free from the physical multi-pion production background. We show the comparison of experimental results with theoretical predictions and appraise the accuracy achieved for the determination of the size of the emission source.
45. Kaon pair production close to threshold
    P. Winter, M. Wolke, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Slemaszko, J. Smyrski, A. Taschner, P. Wustner, Z. Zhang, W. Zipper
    abstract

    PHYSICS LETTERS B 635:1 p. 23-29 (2006)
    The total cross section of the reaction pp -> ppK(+)K(-) has been measured at excess energies Q = 10 MeV and 28 MeV with the magnetic spectrometer COSY-11. The new data show a significant enhancement of the total cross section compared to pure phase space expectations or calculations within a one boson exchange model. In addition, we present invariant mass spectra of two particle subsystems. While the K+K- system is rather constant for different invariant masses, there is an enhancement in the pK(-) system towards lower masses which could at least be partially connected to the influence of the Lambda (1405) resonance. (c) 2006 Elsevier B.V. All rights reserved.
46. Threshold hyperon production in proton-proton collisions at COSY-11.
    T. Rozek, D. Grzonka, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Kowina, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, Z. Zhang, W. Zipper
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    abstract

    Phys. Lett. B643:251-256 (2006)

    HEP: arXiv:nucl-ex/0607034
    Sigma+ hyperon production was measured at the COSY-11 spectrometer via the p p --> n K+ Sigma+ reaction at excess energies of Q = 13 MeV and Q = 60 MeV. These measurements continue systematic hyperon production studies via the p p --> p K+ Lambda/Sigma0 reactions where a strong decrease of the cross section ratio close-to-threshold was observed. In order to verify models developed for the description of the Lambda and Sigma0 production we have performed the measurement on the Sigma+ hyperon and found unexpectedly that the total cross section is by more than one order of magnitude larger than predicted by all anticipated models. After the reconstruction of the kaon and neutron four momenta, the Sigma+ is identified via the missing mass technique. Details of the method and the measurement will be given and discussed in view of theoretical models.
47. Kaon pair production close to threshold.
    P. Winter, M. Wolke, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Wustner, Z. Zhang, W. Zipper
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    abstract

    Phys. Lett. B635:23-29 (2006)

    HEP: arXiv:hep-ex/0602030
    The total cross section of the reaction pp->ppK+K- has been measured at excess energies Q=10 MeV and 28 MeV with the magnetic spectrometer COSY-11. The new data show a significant enhancement of the total cross section compared to pure phase space expectations or calculations within a one boson exchange model. In addition, we present invariant mass spectra of two particle subsystems. While the K+K- system is rather constant for different invariant masses, there is an enhancement in the pK- system towards lower masses which could at least be partially connected to the influence of the Lambda(1405) resonance.
48. A method to disentangle single- and multi-meson production in missing mass spectra from quasi-free pn ---> pn X reactions.
    P. Moskal, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, T. Johansson, B. Kamys, P. Klaja, A. Khoukaz, K. Kilian, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, J. Wessels, P. Winter, M. Wolke, P. Wuestner, Z. Zhang, W. Zipper
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    abstract

    J. Phys.G G32:629-641 (2006)

    HEP: arXiv:nucl-ex/0507033
    The separation of contributions from multi- and single-meson production in the missing mass spectrum of the quasi-free pn --> pnX reaction constitutes a~challenging task when the reaction is studied close to threshold. This is especially true if the resolution of the mass determination is comparable with the excess energy and if the investigated signal appears close to the kinematical limit. In this article we outline a method which permits the extraction of the signal originating from the creation of a single meson without the necessity of conducting model-dependent simulations. For the pd --> pnXp(spectator) reactions, the method allows one to combine events corresponding to multi-meson production at various excess energies with respect to the pn --> pn meson process, and hence leads to an increase of the statistics needed for the determination of the shape of the multi-meson background. As an example of the application of the method, we demonstrate that the evaluation of the data from the pd --> pnXp(sp) process according to the described technique enables one to extract a signal of the pn --> pn eta reaction whose shape is consistent with expectations, supporting the correctness and usefulness of the method introduced.
49. Hadronic interaction of the 77 meson with two nucleons
    P. Moskal, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, J. Majewski, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 20:8-9 p. 1880-1883 (2005)
    The COSY-11 collaboration has conducted experiments aiming at the determination of the excitation function and phase-space population of the pp -> pp eta reaction close to the kinematical threshold. The precise data obtained with the stochastically cooled proton beam of the cooler synchrotron COSY and the high resolution zero-degree magnetic spectrometer allowed for the observation of the significant deviations - in the shape of the excitation function and two-particle invariant masses - from the predictions based on the assumption that the reaction phase space is homogenously populated. Comparison of the shape of the excitation function for the pp -> pp eta and pp -> pp eta' reaction allows to distinquish in the model independent way an influence originating from the protonproton and proton-eta interaction. For the comparison the full data set from experiments performed at COSY and other laboratories is used.
50. Search for Bremsstrahlung radiation in quasi-free np -> np gamma reactions
    J. Przerwa, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, N. Lang, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 20:2-3 p. 625-627 (2005)
    Due to the high sensitivity of the NN -> NN gamma reaction to the nucleon-nucleon potential, Bremsstrahlung radiation is used as a tool to investigate details of the nucleon-nucleon interaction. Such investigations can be performed at the cooler synchrotron COSY in the Research Centre Julich, by dint of the COSY-11 detection system. The results of the identification of Bremsstrahlung radiation emitted via the dp -> dp gamma reaction in data taken with a proton target and a deuteron beam are presented and discussed.
51. Threshold hyperon production at COSY-11
    T. Rozek, D. Grzonka, K. Kilian, P. Kowina, W. Oelert, T. Sefzick, P. Winter, M. Wolke, P. Wustner, M. Siemaszko, W. Zipper, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, J. Smyrski, HH. Adam, A. Khoukaz, R. Santo, A. Taschner, A. Budzanowski
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 20:2-3 p. 680-682 (2005)
    The Lambda, Sigma(0) and Sigma(+) hyperon production in NN collisions is studied at the COSY - 11 installation in order to investigate the production mechanism as well as to extract information about the Y-N interaction.
52. Production of eta mesons in proton-proton collisions close to threshold
    R. Czyzykiewicz, HH. Adam, A. Budzanowski, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Kowina, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 20:2-3 p. 708-711 (2005)
    A brief experimental overview on the close-to-threshold eta meson production in proton-proton interactions is presented and the available observables in measurements with unpolarized and polarized beam and target are discussed.
53. New results on the pd -> He-3 eta production near threshold
    HH. Adam, A. Khoukaz, N. Lang, T. Lister, R. Santo, S. Steltenkamp, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, J. Smyrski, D. Grzonka, K. Kilian, W. Oelert, T. Sefzick, P. Winter, M. Wolke, P. Wustner, A. Budzanowski, T. Rozek, M. Siemaszko, W. Zipper
    abstract

    PROC. INTERNATIONAL JOURNAL OF MODERN PHYSICS A 20:2-3 p. 643-645 (2005)
    Measurements on the eta meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY (Julich). Here we present preliminary results on total and differential cross sections for the pd -> He-3 eta reaction at five excess energies between Q = 5.1 and Q = 40.6 MeV. The obtained angular distributions for the emitted eta mesons in the center of mass system expose a transition from an almost isotropic emission to a highly anisotropic distribution. The extracted total cross sections support a strong eta-He-3 final state interaction and will be compared with model predictions.
54. Drift chamber with a c-shaped frame.
    J. Smyrski, Ch. Kolf, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, A. Heczko, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, A. Misiak, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, C. Quentmeier, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
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    abstract

    Nucl. Instrum. Meth. A541:574-582 (2005)

    HEP: arXiv:nucl-ex/0501023
    We present the construction of a planar drift chamber with wires stretched between two arms of a c-shaped aluminium frame. The special shape of the frame allows to extendthe momentum acceptance of the COSY-11 detection system towards lower momenta without suppressing the high momentum particles. The proposed design allows for construction of tracking detectors covering small angles with respect to the beam, which can be installed and removed without dismounting the beam-pipe. For a three-dimensional track reconstruction a computer code was developed using a simple algorithm of hit preselection.
55. New results on pd -> He-3 eta production from threshold up to Q=40 MeV
    HH. Adam, A. Khoukaz, N. Lang, T. Lister, R. Santo, S. Steltenkamp, R. Czyzykiewicz, M. Janusz, L. Jarczyk, B. Kamys, P. Klaja, P. Moskal, C. Piskor-Ignatowicz, J. Przerwa, J. Smyrski, D. Grzonka, K. Kilian, W. Oelert, T. Sefzick, P. Winter, M. Wolke, P. Wustner, A. Budzanowski, T. Rozek, M. Siemaszko, W. Zipper
    abstract

    PROC. AIP CONFERENCE PROCEEDINGS, Few-Body Problems in Physics 768 p. 209-211 (2005)
    Measurements on the eta meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY (Julich). Here we present preliminary results on total and differential cross sections for the pd -> He-3 eta reaction at five excess energies between Q = 5.1 and Q = 40.6 MeV. The obtained angular distributions for the emitted eta mesons in the center of mass system expose a transition from an almost isotropic emission to a highly anisotropic distribution. The extracted total cross sections support a strong eta-He-3 final state interaction and will be compared with model predictions.
56. Isospin dependence of the eta' meson production in nucleon-nucleon collisions
    J. Przerwa, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, J. Wessels, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. AIP CONFERENCE PROCEEDINGS, Low Energy Antiproton Physics 796 p. 164-167 (2005)
    According to the quark model, the masses of eta and eta' mesons should be almost equal. However, the empirical values of these masses differ by more than a factor of two. Similarly, though they have almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp -> ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp -> pp eta' and pn -> pn eta' total cross sections will allow to learn about the production of the eta' meson in the channels of isospin 1 = 0 and 1 = 1 and to investigate aspects of the gluonium component of the eta' meson.
57. Energy dependence of the Lambda/Sigma(0) production cross-section ratio in p-p interactions
    P. Kowina, M. Wolke, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, J. Haidenbauer, M. Janusz, L. Jarczyk, A. Khoukaz, K. Kilian, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, C. Quentmeier, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, P. Winter, P. Wustner, W. Zipper
    abstract

    EUROPEAN PHYSICAL JOURNAL A 22:2 p. 293-299 (2004)
    The production of the Lambda- and Sigma(0)-hyperous has been measured via the pp --> pK(+)Lambda/Sigma(0) reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the Lambda/Sigma(o) cross-section ratio from about 28 at Q less than or equal to 13 MeV to the high-energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final-state interactions in the p-Sigma(o) channel seem to be much smaller than in the p-A channel. Estimates of the effective range parameters are given for the NLambda and the NSigma systems.
58. Total and differential cross-sections for the pp -> pp eta ' reaction near threshold
    A. Khoukaz, I. Geck, C. Quentmeier, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, L. Jarczyk, K. Kilian, P. Kowina, N. Lang, T. Lister, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, T. Rozek, R. Santo, G. Schepers, T. Sefzick, S. Sewerin, M. Siemaszko, J. Smyrski, A. Strzalkowski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    EUROPEAN PHYSICAL JOURNAL A 20:2 p. 345-350 (2004)
    The eta'-meson production in the reaction pp --> ppeta' has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross-sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near-threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final-state interaction and Coulomb effects. The obtained angular distribution of the eta'-mesons is also consistent with pure s-wave production.
59. Total and differential cross-sections for the pp -> pp eta prime reaction near threshold
    A. Khoukaz, ..., A. Budzanowski, R. Czyżykiewicz, P. Moskal et al.
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    abstract

    Eur. Phys. J. A 20, 345?350 (2004)

    HEP: arXiv:nucl-ex/0401011v1
    The eta-prime meson production in the reaction pp-->pp eta-prime has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final state interaction and Coulomb effects. The obtained angular distribution of the eta-prime mesons is also consistent with pure s-wave production.
60. Experimental study of pp eta dynamics in the pp -> pp eta reaction.
    P. Moskal, ..., H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, M. Siemaszko, J. Smyrski et al.
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    abstract

    Phys.Rev. C69 (2004) 025203

    HEP: arXiv:nucl-ex/0307005
    A high statistics measurement of the pp --> ppeta reaction at an excess energy of Q = 15.5 MeV has been performed at the internal beam facility COSY-11. The stochastically cooled proton beam and the used detection system allowed to determine the momenta of the outgoing protons with a precision of 4 MeV/c (sigma) in the center-of-mass frame. The determination of the four-momentum vectors of both outgoing protons allowed to derive the complete kinematical information of the ppeta-system. An unexpectedly large enhancement of the occupation density in the kinematical regions of low proton-eta relative momenta is observed. A description taking the proton-proton and the eta-proton interaction into account and assuming an on-shell incoherent pairwise interaction among the produced particles fails to explain this strong effect. Its understanding will require a rigorous three-body approach to the ppeta system and the precise determination of contributions from higher partial waves. We also present an invariant mass spectrum of the proton-proton system determined at Q = 4.5 MeV. Interestingly, the enhancement at large relative momenta between protons is visible also at such a small excess energy. In contrast to all other determined angular distributions, the orientation of the emission plane with respect to the beam direction is extracted to be anisotropic.
61. Production of eta and eta ' mesons via the quasi-free proton-neutron interaction
    P. Moskal, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, T. Johansson, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, A. Strzalkowski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. AIP Conference Proceedings, HADRON SPECTROSCOPY 717 p. 907-911 (2004)
    A comparison of the close-to-threshold total cross sections for the eta' meson production in both the pp --> ppeta' and pn --> pneta' reactions should provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta' meson and the relevance of quark-gluon or hadronic degrees of freedom in the creation process. The excitation function for the reaction pp --> ppeta' has been already established. At present, experimental investigations of the quasi-free pn --> pnX reactions are carried out at the COSY-11 facility using a beam of stochastically cooled protons and the deuteron cluster target. A method of measurement and preliminary results from the test experiments of the pn --> pneta reaction are presented in this report.
62. Energy dependence of the Lambda/Sigma(0) production cross section ratio in p-p interactions.
    P. Kowina, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. AIP Conference Proceedings, HADRON SPECTROSCOPY 717 p. 852-857 (2004)
    Measurements of the near threshold Lambda and Sigma(0) production via the pp --> pK(+)Lambda/Sigma(0) reaction at COSY-11 have shown that the Lambda/Sigma(0) cross section ratio exceeds the value at high excess energies (Q greater than or equal to 300 MeV) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. Within the first 20 MeV excess energy a strong decrease of the cross section ratio is observed, with a less steep decrease in the higher excess energy range. A description of the data with a parametrisation including p - Y final state interactions suggests a much smaller p - Sigma(0) FSI compared to the p - Lambda system.
63. Analysis of the eta meson production mechanism via the (p)over-barp -> pp eta reaction
    R. Czyzykiewicz, HH. Adam, A. Budzanowski, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, P. Wustner, W. Zipper
    abstract

    PROC. AIP CONFERENCE PROCEEDINGS, HADRON SPECTROSCOPY 717 p. 858-862 (2004)
    Polarisation observables constitute a powerful tool for establishing the production mechanism of the eta meson and for infering the presence of higher partial waves in the final system. Measurements of the proton analysing power for the (p) over right arrowp --> ppeta reaction have been performed by the COSY-11 group at three different excess energies: Q = 10, 37 and 40 MeV. Data at Q = 40 MeV indicate that the eta meson is probably produced in partial waves higher than s wave.
64. Associated strangeness production at threshold
    P. Kowina, M. Wolke, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, T. Lister, P. Moskal, W. Oelert, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, P. Winter, P. Wustner, W. Zipper
    abstract

    PROC. EUROPEAN PHYSICAL JOURNAL A 18:2-3 p. 351-354 (2003)
    The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon and the K (+) K(-) meson pair production. Measurements of the near-threshold Lambda and Sigma(o) production via the pp --> pK(+) Lambda/Sigma(0) reaction (S. Sewerinet al., Phys. Rev. Lett. 83, 682 (1999)) at COSY-11 have shown that the Lambda/Sigma(o) cross-section ratio exceeds the value at high excess energies (Q greater than or equal to 300 MeV (A. Baldiniet al., Total Cross-Sections for Reactions of High-Energy Particles, Landolt-Bornstein, New Series, Vol. I/12 (Springer, Berlin, 1988))) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near-threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c(2) mass range, i.e. the f(0)(980) and a(0)(980) (O. Krehl, R. Rapp, J. Speth, Phys. Lett. B 390, 23 (1997)). The interpretation as a K (K) over bar molecule is strongly dependent on the K-(K) over bar interaction which can be studied via the production channel. A first total cross-section value on the reaction pp --> pp K(+) K(-) at an excess energy of 17 MeV (C. Quentmeieret al., Phys. Lett. B 515, 276 (2001)), i.e. below the phi production threshold, was measured.
65. First close-to-threshold measurement of the analysing power A(y) in the reaction (p)over-right-arrowp -> pp eta
    P. Winter, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, T. Lister, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, A. Taschner, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. EUROPEAN PHYSICAL JOURNAL A 18:2-3 p. 355-357 (2003)
    At the internal facility COSY-11 a first measurement of the reaction (p) over right arrowp --> ppeta near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one-meson exchange models will be discussed.
66. Upper limit for the cross-section of the overlapping scalar resonances f(0)(980) and a(0)(980) produced in proton-proton collisions in the range of the reaction threshold
    P. Moskal, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, C. Kolf, P. Kowina, T. Lister, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, C. Quentmeier, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, A. Strzalkowski, A. Taschner, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 29:9 PII S0954-3899(03)64403-8 p. 2235-2245 (2003)
    Utilizing a missing mass technique we investigate the pp --> ppX reaction scanning beam energies in the range permitting to create a mass close to that of the f(0) (980) and a(0) (980) scalar resonances, but still below the K+ K- threshold where they decay dominantly into pi pi and pi eta mesons, respectively. Prior to the data analysis we introduce a notion of the close to threshold total cross-section for broad resonances. We estimated for the overlapping mesons a(0) and f(0) the total cross-section to be smaller than 430 nb at excess energy of Q = 5 MeV. The experiment has been performed at the Cooler Synchrotron (COSY) using the COSY-11 facility.
67. Upper limit for the cross-section of the overlapping scalar resonances f(0)(980) and a(0)(980) produced in proton proton collisions in the range of the reaction threshold
    P. Moskal, ..., H. H. Adam, A. Budzanowski, R. Czyżykiewicz, D. Grzonka, K. Kilian et al.
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    abstract

    J.Phys.G G29 (2003) 2235-2246

    HEP: arXiv:nucl-ex/0307016
    Utilizing a missing mass technique we investigate the pp ? ppX reaction scanning beam energies in the range permitting to create a mass close to that of the f0(980) and a0(980) scalar resonances, but still below the K+K? threshold where they decay dominantly into ?? and ?? mesons, respectively. Prior to the data analysis we introduce a notion of the close to threshold total cross-section for broad resonances. We estimated for the overlapping mesons a0 and f0 the total cross-section to be smaller than 430 nb at excess energy of Q = 5 MeV. The experiment has been performed at the Cooler Synchrotron (COSY) using the COSY-11 facility.
68. Hadronic interaction of eta and eta ' mesons with nucleons
    P. Moskal, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, T. Lister, W. Oelert, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. NUCLEAR PHYSICS A 721 p. 657C-660C (2003)
    Due to their short life-time, flavour-neutral mesons cannot be utilized as free secondary beams or targets, and therefore a study of their interaction with nucleons is not possible via direct scattering experiments. It is, however, accessible via its influence on the energy dependence - and on the phase space distributions of the cross sections for reactions in which these mesons are produced. In case of the pp --> ppeta reaction the experimentally determined distributions of the differential cross sections close to the production threshold cannot be described by taking into account the S-wave proton-proton and proton-eta interaction only. Here we show that the angular distributions determined at the COSY-11 facility reveal some evidence for P-wave admixture in the proton-proton subsystem already at an excess energy as low as Q = 15.5 MeV. We also present that one can estimate the relative strength of the eta-nucleon and eta'-nucleon interactions by comparison of the eta and eta' production yield.
69. Strangeness production in proton-proton collisions close to threshold
    M. Wolke, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Kowina, T. Lister, P. Moskal, W. Oelert, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, P. Winter, P. Wustner, W. Zipper
    abstract

    PROC. NUCLEAR PHYSICS A 721 p. 683C-686C (2003)
    Exclusive data on the reactions pp --> ppK(+)K(-) and pp --> pK(+Lambda)/Sigma(0) have been taken at the cooler synchrotron COSY close to threshold. At equal excess energies, an enhancement of the Lambda/Sigma(0) ratio by one order of magnitude has been observed compared to data at higher excess energies. New results obtained at the COSY-11 facility explore the transition region between this low-energy Sigma(0) suppression and excess energies of 60 MeV. A first total cross section for elementary antikaon production below the phi threshold has been determined, two orders of magnitude smaller compared to kaon production at the same excess energy.
70. Study of the eta proton interaction via the reaction p p -> p p eta.
    P. Moskal, ..., H.H. Adam, A. Budzanowski, R. Czyzykiewicz, T. Gotz, D. Grzonka, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, et al.
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    abstract

    PiN Newslett. 16 (2002) 367-369

    HEP: arXiv:nucl-ex/0110018
    A measurement of the pp --> p p eta reaction at the excess energy of Q = 15.5 +- 0.4 MeV has been carried out at the internal beam facility COSY-11 with an integrated luminosity of 811 nb^-1 The number of ~24000 identified events permits a precise determination of total (2.32 +- 0.05 +- 0.35 mu b) and differential cross sections. Preliminary investigations show that the angular distribution of the eta meson in the center-of-mass system is isotropic. A qualitative analysis of the Dalitz-plot distribution is presented.
71. Analysing power A y in the reaction (p)over-right-arrowp -> pp eta close to threshold
    P. Winter, HH. Adam, F. Bauer, A. Budzanowski, R. Czyzykiewicz, T. Gotz, D. Grzonka, L. Jarczyk, A. Khoukaz, K. Kilian, C. Kolf, P. Kowina, N. Lang, T. Lister, P. Moskal, W. Oelert, C. Quentmeier, T. Rozek, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, S. Steltenkamp, A. Strzalkowski, M. Wolke, P. Wustner, W. Zipper
    abstract

    PHYSICS LETTERS B 544:3-4 PII S0370-2693(02)02417-6 p. 251-258 (2002)
    Measurements of the eta meson production with a polarised proton beam in the reaction (p) over barp --> ppeta have been carried out at an excess energy of Q = 40 MeV. The dependence of the analysing power A,. on the polar angle theta(q)(*) of the 17 meson in the q center of mass system (CMS) has been studied. The data indicate the possibility of an influence of p- and d-waves to the close to threshold 17 production. (C) 2002 Elsevier Science B.V. All rights reserved.
72. Experimental results on strangeness production in proton-proton collisions at COSY
    P. Moskal, HH. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, C. Kolf, L. Jarczyk, A. Khoukaz, K. Kilian, P. Kowina, N. Lang, T. Lister, W. Oelert, C. Quentmeier, R. Santo, G. Schepers, T. Sefzick, M. Siemaszko, J. Smyrski, A. Strzalkowski, P. Winter, M. Wolke, P. Wustner, W. Zipper
    abstract

    PROC. JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 28:7 PII S0954-3899(02)32425-3 p. 1777-1786 (2002)
    The production of K+ and K- mesons in elementary proton-proton collisions has been investigated at the Cooler synchrotron COSY in Julich. A high quality proton beam with low emittance and small momentum spread permitted study of the creation of these mesons very close to the kinematical threshold. The energy dependence of the total cross section is investigated using internal beam facilities providing a high accuracy particle momentum determination as well as an external non-magnetic detection setup with a large geometrical acceptance. The determination of the four-momentum vectors for all ejectiles of each registered event gives the complete kinematical information allowing study of the interaction of the outgoing particles. Results on the performed studies of the pp --> ppK(+)K(-), pp --> pLambdaK(+) and pp --> pSigma(0)K(+) reactions will be presented and their relevance to the interpretation of heavy ion collisions will be discussed.

1. Dynamics of the near threshold eta meson production in proton-proton interaction
   P. Moskal, R. Czyżykiewicz, H.-H. Adam, A. Budzanowski, E. Czerwiński, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, P. Winter, M. Wolke, P. Wüstner, M. Zieliński, W. Zipper
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   published in: Proceedings of The 11th Workshop on The Physics of Excited Nucleons, 5?8 September 2007, Bonn, Germany
   We present the results of measurements of the analysing power for the p(pol)p --> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret these results within the framework of the meson exchange models. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in s-wave.
2. Comparative Studies of Low Energy ppeta and ppeta-prime Systems with Cosy-11 Detector.
   P. Klaja, R. Czyżykiewicz, P. Moskal
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   published in: Acta Phys. Pol. Supp. 2 (2009) 45-50
   We present a comparison of the two-body invariant mass distributions for the pp -> ppeta and pp -> ppeta-prime reactions, both measured at a nominal excess energy value of Q = 15.5 MeV. For the pp -> ppeta reaction, in addition, the differential cross sections were extracted for an excess energy of Q = 10 MeV. The comparison of the results for the eta and eta-prime meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the interaction of the meson and the proton.
3. Near threshold production of the pseudoscalar mesons at the COSY-11 facility
   P. Moskal, R. Czyżykiewicz, H.-H. Adam, A. Budzanowski, E. Czerwiński, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, J. Smyrski, A. Täschner, P. Winter, M. Wolke, P. Wüstner, M. Zieliński, W. Zipper
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   published in: Proceedings of The 11th Workshop on The Physics of Excited Nucleons, 5?8 September 2007, Bonn, Germany
   We summarise measurements of the COSY-11 collaboration concerning the excitation functions of the near threshold pseudoscalar meson production in the proton-proton interaction. The results are discussed in the context of the meson-nucleon and hyperon-nucleon interactions. We conclude that the $eta$-proton interaction is significantly stronger than the eta'-proton interaction. Similarly, we found that the hyperon Lambda interacts with the nucleon considerably stronger than the hyperon Sigma, and that the interaction of (K-)-proton is much stronger than this of the (K+)-proton
4. Study of the hadronic production of kaon pairs below the threshold for the phi meson
   P. Moskal, M. Silarski, A. Budzanowski, E. Czerwiński, R. Czyżykiewicz, D. Gil, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, B. Rejdych, J. Ritman, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taschner, P. Winter, M. Wolke, P. Wustner, M. Zieliński, W. Zipper, J. Zdebik
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   published in: Nucl. Phys. Proc. Suppl.181-182:194 (2008)
   The near threshold production of K+K- pairs in proton-proton collisions has been investigated at the cooler synchrotron COSY below and above the threshold for the phi meson using the COSY-11 and ANKE facilities, respectively. The excitation function determined for the pp ->ppK+K- reaction revealed a statistically significant enhancement close to the threshold which may plausibly be assigned to the influence of the K-p interaction. In addition, observed consistently by both groups, a strong enhancement at low values of the ratio of the K-p to K+p invariant mass distributions shows that the proton interacts much stronger with K- than with K+. In this report we focus on the measurements performed by the COSY-11 collaboration. We explain the experimental method used and present main results of completed analyses as well as a new qualitative elaboration of the ppK+K- events population on the Goldhaber plot. We conclude with the observation that event densities increase at the region where the influence from the K+K- interaction is expected.
5. Luminosity determination for the quasi-free nuclear reactions.
   R. Czyżykiewicz, P. Moskal, E. Czerwiński, J. Klaja, P. Klaja, M. Zieliński, M. Silarski et al.
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   published in: AIP Conf.Proc. 950 (2007) 118-124
   A method for the calculation of the luminosity for the proton-nucleus collisions based on the quasi-free proton-proton scattering is presented. As an example of application the integrated luminosity for the scattering of protons off the deuteron target is determined for the experiment of the quasi-free pn --> pneta reaction performed by means of the COSY-11 facility.
6. COSY-11: An Experimental facillity for studying meson production in free and quasi-free nucleon-nucleon collisions.
   P. Klaja, H.-H. Adam, A. Budzanowski, R. Czyzykiewicz, D. Grzonka, M. Janusz, L. Jarczyk, B. Kamys, A. Khoukaz, K. Kilian, P. Moskal, W. Oelert, C. Piskor-Ignatowicz, J. Przerwa, J. Ritman, T. Rozek, T. Sefzick, M. Siemaszko, J. Smyrski, A. Taeschner, J. Wessels, P. Winter, M. Wolke, P. Wuestner, W. Zipper
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   published in: AIP Conf. Proc. 796:160-163 (2005)
   The COSY-11 experimental setup is an internal facility installed at the COoler SYnchrotron COSY in Juelich. It allows to investigate meson production in free and quasi-free nucleon-nucleon collisions, eg. pp --> pp meson and pd --> p_sp np meson reactions. Drift chambers and scintillators permit to measure outgoing protons, separated in magnetic field of COSY-11 dipole. Neutrons are registered in the neutron modular detector installed downstream the beam. Recently, the experimental setup has been extended with spectator detector, deuteron drift chamber and polarization monitoring system, and since then meson production can be investigated also as a function of spin and isospin of colliding nucleons.

1. Study of the interaction of eta and eta-prime mesons with protons.
   J. Przerwa, R. Czyżykiewicz, M. Janusz, P. Klaja, P. Moskal
   LEAP Conference, Bonn 2005

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