PHOTOPRODUCTION OF η-MESONS AND ηπ-PAIRS OFF LIGHT NUCLEI

被引:4
作者
Krusche, B. [1 ]
机构
[1] Univ Basel, Dept Phys, CH-4003 Basel, Switzerland
来源
ACTA PHYSICA POLONICA B | 2014年 / 45卷 / 03期
关键词
NEAR-THRESHOLD PHOTOPRODUCTION; COHERENT PHOTOPRODUCTION; BEAM ASYMMETRY; CROSS-SECTION; QUASI-FREE; EXCLUSIVE MEASUREMENT; PROTON; RESONANCES; S-11(1535); SIGMA;
D O I
10.5506/APhysPolB.45.639
中图分类号
O4 [物理学];
学科分类号
0702 ;
摘要
Photoproduction of eta-mesons has been measured for several light nuclei (H-2, He-3, Li-7) and photoproduction of eta pi-pairs was investigated for a deuteron target. The experiments were done at the tagged photon beam of the Mainz MAMI accelerator with the Crystal Ball/TAPS electromagnetic calorimeter. They aimed at two topics: the extraction of cross section data for the elementary reactions off neutrons and the investigation of the eta-nucleus interactions, in view of eta-mesic states. The main results are: the excitation function for the gamma n -> n eta reaction has a very narrow structure (width around 30 MeV) at final state invariant masses of 1670 MeV. Its nature is not yet understood. For the quasi-free production of eta pi-pairs, the analysis of all isospin channels (final states p eta pi r(0), n eta pi(0), p eta pi(-), and n eta pi(+)) resulted in cross section ratios almost perfectly agreeing in the threshold region with a dominant contribution from the D-33 -> eta P-33(1232) ->eta pi N decay chain. The measurement of coherent eta-production off 3He and 7Li nuclei confirmed a strong threshold enhancement accompanied by almost isotropic angular distributions for the He-3 nucleus and much smaller deviations from PWIA approximations for the 7Li nucleus, supporting the special role of He-3 as a candidate for eta-mesic nucleus formation.
引用
收藏
页码:639 / 653
页数:15
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