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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 Pheron — aInstitut 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.