Meson-production experiments at COSY-Juelich

Selected results from experiments at COSY-Juelich are presented: an attempt to measure the mass of the eta meson with high precision (ANKE facility), first steps towards the detection of rare eta decays (WASA), and several measurements of KKbar-pair production (ANKE, COSY-11, MOMO).Comment: Proceedings of QNP2009, Beijing, Sept. 2009; to be published in Chinese Physics C. 6 pages, 5 figure

Event Reconstruction for a DIRC

Monte Carlo simulations were made for a possible DIRC at the WASA detector at COSY. A statistical method for pattern recognition is presented and the possible angle resolution and velocity precision achieved are discussed.Comment: Minor changes in text. Figures updated. accepted by JINS

High precision measurement of the associated strangeness production in proton proton interactions

A new high precision measurement of the reaction pp -> pK+Lambda at a beam momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed analysis of differential observables and their inter-dependencies. Correlations of the angular distributions with momenta are examined. The invariant mass distributions are compared for different regions in the Dalitz plots. The cusp structure at the N Sigma threshold is described with the Flatt\'e formalism and its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.

Reeconstructing Sigma0 decays in STAR

Typical comparisons of data from nuclear collisions to particle production models require a caveat for (anti)Lambda yields from experimental inability to separate the contributions of those yields from Sigma state decays. Recent analysis in STAR is leading toward resolving the contribution from excited Sigma states, but the bulk contribution comes from electromagnetic decays of the (anti)Sigma0. In the STAR detector, photon conversions into e+e- pairs in the detector material have been used to identify photons from pi0 decays. A similar technique has been used here to identify photons from (anti)Sigma0 decays in conjunction with STAR's excellent PID capabilities for finding the associated (anti)Lambda daughters. We report here on progress toward measuring the (anti)Sigma0 yields in various nuclear collisions at RHIC.Comment: 8 pages, 5 figures, proceedings of Hot Quarks 2004 workshop, submitted to J. Phys.

First Model-Independent Measurement of the Spin Triplet pΛp\Lambda Scattering Length from Final State Interaction in the p⃗p→pK+Λ\vec{p}p \rightarrow pK^{+}\Lambda Reaction

The $\vec{p}p \rightarrow pK^{+}\Lambda$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $p\Lambda$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm 0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.Comment: Revised version as accepted for publication in PR

Search for the Θˉ−→\bar{\Theta}^- \to K−^- nˉ\bar{n} with PHENIX

The PHENIX experiment at RHIC should be sensitive to decays of the the anti--pentaquark $\bar{\Theta}^-$ via the K$^-$ $\bar{n}$ channel. Charged kaons can be identified using the standard tracking and time of flight up to a momentum of 1.5 GeV/c. Anti--neutron candidates are detected via their annihilation signal in the highly segmented electromagnetic calorimeter (EMCal). In order to assess the quality of the anti--neutron identification we reconstruct the $\bar{\Sigma} \to \bar{n}\pi$. As an additional crosscheck the invariant mass of K$^+$ $\bar{n}$ is reconstructed where no resonance in the pentaquark mass range is expected. At the present time no enhancement at the expected pentaquark mass is observed in dAu collisions at $\sqrt{s_{NN}} = 200 GeV.Comment: 4 pages 5 figures contribution to the proceedings of the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter, Oakland, January 11-17, 2004). To appear in the proceedings (Journal of Physics G

Tests of the fundamental symmetries in eta meson decays

Patterns of chiral symmetry violation and tests of the conservation of the fundamental C, P and CP symmetries are key physics issues in studies of the pi0, eta and eta' meson decays. These tests include searches for rare or forbidden decays and searches for asymmetries among the decay products in the not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0 (CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta' meson decays are carried out at four European accelerator research facilities: KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY (J\"ulich), Crystal Barrel at ELSA (Bonn).Comment: 9 pages, 2 figures, proceedings of Symposium on Prospects in the Physics of Discrete Symmetries, DISCRETE 2010, 6 - 11 December, Rome; v2: added reference

Luminosity determination for the pd reaction at 2.14 GeV with WASA-at-COSY

The luminosity for a WASA-at-COSY experiment involving the pd reaction at 2.14 GeV proton-beam energy is determined by the forward pd elastic scattering, which yields an average beam-on-target value of [5.2\pm0.3(stat)\pm0.3(syst)]*10^{30} s^{-1}cm^{-2}. In addition, the forward pd elastic-scattering angular distribution is obtained with four-momentum transfer squared -t between 0.16 (GeV/c)^{2} and 0.78 (GeV/c)^{2} at this beam energy, which is compared with other experimental data and the pd double scattering model.Comment: 5 pages, 6 figure

Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4He{\pi}0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13(sys) +- 8(ext)) pb and first data on the differential cross section are consistent with s-wave pion production.Comment: 14 pages, 5 figure

Chiral perturbation theory calculation for pn -> dpipi at threshold

We investigate the reaction pn -> dpipi in the framework of Chiral Perturbation Theory. For the first time a complete calculation of the leading order contributions is presented. We identify various diagrams that are of equal importance as compared to those recognized in earlier works. The diagrams at leading order behave as expected by the power counting. Also for the first time the nucleon-nucleon interaction in the initial, intermediate and final state is included consistently and found to be very important. This study provides a theoretical basis for a controlled evaluation of the non-resonant contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table