Bonn 2010 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 26: Hadronenstruktur und -spektroskopie VI

HK 26.6: Vortrag

Dienstag, 16. März 2010, 18:00–18:15, HG IV

η photoproduction off 3He : Search for η-mesic nuclei — •Francis PheronaInstitut fuer Physik,Universität Basel, Klingelbergstrasse 82, CH-4056 Basel , (francis.pheron@unibas.ch).

Photoproduction of η-mesons off 3He has been studied via the η→2γ and η→3π0 decay modes at the tagged photon beam of the Mainz MAMI accelerator using the combined 4π Crystal Ball/TAPS calorimeter. In a previous experiment, Pfeiffer et al. had reported evidence (although at low statistical significance) for the formation of a quasi-bound η-3He state. The present experiment aimed at an improved statistical quality for both the excitation function of coherent photoproduction on η-mesons off 3He and the peak-like structure in the excitation function of πo-p back-to-back pairs [1]. The η-mesons have been identified by an invariant mass analysis of 2-photons (respectively 6-photons) events. In the both case also the constraints from the intermediate πo-invariant masses have been used.
The coherent reaction γ3He→η3He has been selected by the suppression of events with observed recoil nucleons and by a missing energy analysis. Preliminary results for the excitation function show an extremely rapid rise at the production threshold similar to what has been observed in hadronic induced reactions at COSY [T.Mersmann et al.]. At the same time excitation function of πo-p pair shows the peak-like structure at the η-production threshold with much better statistic quality then the previous experiment. Altought strong evidence for the existence of a resonance state has been formed.

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