München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 2: Elektromagnetische und Hadronische Sonden

HK 2.1: Gruppenbericht

Montag, 20. März 2006, 14:00–14:30, F

$∖eta$ and $∖eta^{’}$ photoproduction on deuteron — •Jaegle Igal — Universit∖No-dqat Basel, CH-4056 Basel, Klingelbergst. 82

A study of the photoproduction of the isoscalars $∖eta$ and $∖eta^{’}$ on the deuteron has been done at the tagged photon beam of the Bonn ELSA accelerator with a combined setup of the Crystal Ball and TAPS detectors, which formed a $4∖pi$ electromagnetic calorimeter. The aim of the study is to observe and identify individual N$^*$ states of masses between 1.5GeV and 2.2GeV with strong photocouplings to the neutron. The mesons were detected in coincidence with the (participant) recoil nucleons, so that the reactions on the proton and on the neutron can be compared. For $∖eta$ - mesons previous experiments have determined a neutron - proton cross section ratio of $2 / 3$ in the excitation energy range of the $S_{11}(1535)$. Models predict a strong rise of the ratio at higher energies due to the contribution from other resonances such as the $D_{15}(1675)$. The data show indeed a bump like structure in this energy region which is not observed for the proton. An alternative explanation could be photoexcitation of the non-strange pentaquark state, which is associated with the second member of an antidecuplet of exotic baryons. Angular distributions and photon beam asymetries will be analysed in view of these effects. The measurement of $∖eta^{’}$ production is the first attempt to study this reaction on the neutron. First preliminary results will be discussed.