Search for the eta-mesic nuclei by means of COSY-11, WASA-at-COSY and COSY-TOF detector systems

We review status and perspectives of the search for the light eta-mesic nuclei using COSY-11, WASA-at-COSY and COSY-TOF detector systems.Comment: Invited talk at the International Symposium on Mesic Nuclei, Krakow, 16 June 201

Search for eta-mesic helium using the WASA-AT-COSY detector

We conduct a search for the 4He-eta bound state with the WASA-at-COSY facility via the measurement of the excitation function for the reaction dd->3Heppi-. In first experiment performed in June 2008, we used COSY deuteron beam with a slowly ramped beam momentum corresponding to a variation of the excess energy for the 4He-eta system from -51.4 MeV to 22 MeV. Here we report on the status of the measurement and the data evaluation.Comment: Presented at Symposium on Meson Physics: extended COSY-11 collaboration meeting, Cracow, Poland, 1-4 Oct 2008, 8 pages, 5 figures

Study of the Low Energy Dynamics in the ppK+K- System with the Cosy-11 Magnetic Spectrometer

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 production. The experimental excitation function determined for the pp-->ppK+K- reaction differs from theoretical expectations including proton-proton final state interaction. The discrepancy may be assigned to the influence of K+K- or pK interaction. In this article we present distributions of the cross section for the pp-->ppK+K- reaction as a function of the invariant masses of two and three particle subsystems at excess energies of Q=10 MeV and 28 MeV.Comment: Presented at the Symposium on Meson Physics, Cracow, 01-04 October 200

Search for eta-mesic Helium with the WASA-at-COSY detector

A search for the 4He-eta bound state via exclusive measurement of the excitation function for the dd->3Heppi- reaction, was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta production in the dd -> 4He-eta reaction at 2.336 GeV/c. The corresponding excess energy in the 4He-eta system varied from -51.4 MeV to 22 MeV. The shape of the excitation function for the dd -> 3Heppi- was examined. No signal of the 4He-eta bound state was observed in the excitation function.Comment: 4 pages, 5 figures, to appear in proceedings of MESON201

Near threshold eta meson production in dp collisions

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.Comment: Talk given at 9th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 9-13 June 2006. 5 pages, 3 figure

Determination of the eta'-proton scattering length in free space

Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton-beam of the Cooler Synchrotron COSY we determine the excitation function for the pp --> pp eta' reaction close-to-threshold. Combining these data with previous results we extract the scattering length for the eta'-proton potential in free space to be Re(a_{p eta'}) = 0+-0.43 fm and Im(a_{p eta'}) = 0.37(+0.40)(-0.16) fm.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let

Monitoring of the accelerator beam distributions for internal target facilities

We describe a direct method for monitoring the geometrical dimensions of a synchrotron beam at the target position for internal target installations. The method allows for the observation of the proton beam size as well as the position of the beam relative to the target. As a first demonstration of the technique, we present results obtained by means of the COSY-11 detection system installed at the cooler synchrotron COSY. The influence of the stochastic cooling on the COSY proton beam dimensions is also investigated.Comment: 7 pages, 8 figures, Submitted to Nucl. Inst. & Meth.

Search for Low Mass Exotic mesonic structures. Part I: experimental results

Recently, several papers discussed on the existence of a low mass new structure at a mass close to M=214.3 MeV. It was suggested that the $\Sigma^{+}$ disintegration: $\Sigma^{+}\to$pP$^{0}$, P$^{0}\to\mu^{-}\mu^{+}$ proceeds through an intermediate particle P$^{0}$ having such mass. The present work intends to look at other new or available data, in order to observe the eventual existence of small narrow peaks or shoulders in very low mesonic masses. Indeed narrow structures were already extracted from various data in dibaryons, baryons and mesons (at larger masses that those studied here).Comment: 7 pages 11 figure

Determination of the total width of the eta' meson

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' meson was measured with a resolution of 0.33 MeV/c^2 (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' events the total width of the eta' meson was determined to be 0.226 +- 0.017(stat.) +- 0.014(syst.) MeV/c^2.Comment: 4 pages, 4 figure