Search

The γp→ηp reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold to 1.4 GeV (1.49≤W≤1.87 GeV). Bremsstrahlung photons produced by the 1.5‐GeV electron beam of the Mainz Microtron MAMI‐C and momentum analyzed by the Glasgow Tagging Spectrometer were used for the η‐meson production. Our accumulation of 3.8×106 γp→ηp→3π0p→6γp events allows a detailed study of the reaction dynamics. The γp→ηp differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W = 1680 MeV in the total cross section related to a substantial dip in η production at forward angles. The data are compared to predictions of previous SAID and MAID partial‐wave analyses and to the latest SAID and MAID fits that included our data.

High-resolution spectrometer measurements of the reaction H(e,e' K+)X at small Q2 are used to extract the mass and width of the Lambda(1520). We investigate dependence of the resonance parameters on different parametrizations of the background and the resonance peak itself. Our final values for the Breit-Wigner parameters are M=1520.4+-0.6(stat)+-1.5(syst) MeV and Gamma=18.6+-1.9(stat)+-1(syst) MeV. The width appears to be more sensitive to the assumptions than the mass. We also estimate, for the first time, the pole position for this resonance and find that both the pole mass and width seem to be smaller than their Breit-Wigner values., Comment: 4 pages, 1 figure, to appear in the proceedings of MENU 2010

Given the existing empirical evidence for an exotic Θ+ baryon, we analyze possible properties of its SU(3)F‐partners, paying special attention to the nonstrange member of the antidecuplet N*. A modified πN partial‐wave analysis results in two candidate masses, 1680 MeV and 1730 MeV. In both cases, the N* should be rather narrow and highly inelastic. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons. Recent experimental evidence from the GRAAL and STAR Collaborations could be interpreted as observations of a candidate for the Θ+ nonstrange partner. We also briefly discuss recent negative results regarding the Θ‐baryon.

We review our recent work on the two‐nucleon system. In particular, we concentrate on analyses of the πd elastic and πd→pp scattering data bases. We discuss some problems arising in these analyses and combined analyses which include pp elastic scattering data.

Preliminary results of search for exotic states in 1 GeV proton−nucleus collisions are presented. (AIP)