Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 48: Electromagnetic Probes VII, Electro-, Photoproduction
HK 48.1: Group Report
Wednesday, March 18, 1998, 14:00–14:30, B
Threshold π0 Electro Production off the Proton and off the Deuteron [1] — •Harald Merkel — Institut für Kernphysik, Universität Mainz
Chiral perturbation theory (ChPTh) is an effective field theory to approximate QCD at the confinement scale by utilising the chiral symmetry of the QCD Lagrangian. Up to now, ChPTh is limited to small 4-momentum transfers and to an energy range very close to reaction threshold.
To check predictions of ChPTh, the reactions p(e,e′p)π0 and d(e,e′d)π0 very close to threshold (Δ W < 4 MeV) and at small 4-momentum transfers (−q2 < 0.1 GeV2/c2) were measured with the three spectrometer setup at the Mainz Microtron (MAMI) with full Rosenbluth separation. At threshold, the “kinematical focusing” of the recoil particle (p or d) can be used to accept the whole CMS angular range within the solid angle of a high resolution spectrometer. The π0 were identified by missing mass.
Results for p(e,e′p)π0 at −q2 = 0.1 GeV2/c2 will be presented. The transverse and longitudinal structure functions were determined by LT separation, the transverse-transverse and transverse-longitudinal structure functions were extracted from the angular distribution. First results for smaller values of −q2 will be shown.
To access the neutron amplitude first measurements of the coherent production off the deuteron were performed at −q2 = 0.1 GeV2/c2 and will be presented.
[1] supported by Deutsche Forschungsgemeinschaft (SFB 201)