Antikaon angular distributions in the reaction γd→K−Θ+p→K−K+np{\gamma}d \to K^-{\Theta}^+p \to K^-K^+np near the threshold and the parity of the Θ+{\Theta}^+ pentaquark

Within spectator model we study the reaction ${\gamma}d \to K^-{\Theta}^+p \to K^-K^+np$ in the threshold energy region. We present the predictions for the exclusive and inclusive antikaon angular distributions in the laboratory system for this reaction calculated for two possible parity states of the ${\Theta}^+$ resonance at 1.5 and 1.75 GeV beam energies with and without imposing the relevant kinematical cuts on those parts of the sampled phase space where contribution from the main background sources associated with the ${\phi}(1020)$, ${\Lambda}(1520)$ production as well as with the $K^-p$--rescattering in the final state, is expected to be dominant. We show that under chosen kinematics these distributions are sensitive to the ${\Theta}^+$ parity and, therefore, can be used as a filter for the determination of its parity.Comment: 18 pages, 8 figures; will be published in Phys.Atom.Nucl_4_200

Single pion production in np collisions for excess energies up to 90 MeV

The quasifree reaction np --> pp pi(-) was studied in a kinematically complete experiment by bombarding a liquid-hydrogen target with a deuteron beam of momentum 1.85GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector P-n which differed from event to event. A range of almost 90 MeV excess energy above threshold was covered. Energy-dependent angular distributions, invariant-mass spectra as well as fully covered Dalitz plots were deduced. Sizeable pp FSI effects were found as were contributions of p and d partial waves. In comparison with existing literature data the results provide a sensitive test of the spectator model. The behavior of the elementary cross-section sigma(01) close to threshold is discussed in view of new cross-section data

Analyzing power Ay for omega meson production in proton-proton collisions

We report on a determination of the analyzing power A(y) in the (p) over right arrowp -> pp omega reaction studied with the TOF spectrometer located at the COSY-accelerator (Forschungszentrum Julich, Germany). This spectrometer is very well suited for polarization measurements due to its rotational symmetry and full coverage of the azimuthal angle. For a beam momentum of p = 3065 MeV/c corresponding to an excess energy of epsilon = 129 MeV A(y) is found to be compatible with zero. (c) 2008 Published by Elsevier B.V