Proton Compton effect in the region of the Δ(1236)-resonance

Abstract

which is stronger by more than two orders of magnitude. This le t ter reports on a new measurement of differential cross-sections in the region of the first resonance. The experiment has been carried out at the 500 ~r synchrotron of the Bonn Universi ty with an apparatus consisting of two counter telescopes in which both the recoil proton and the photon have been detected in coincidence, The experimental lay-out is sketched in Fig. 1. The recoil protons are identified in angle and energy by a range telescope which has been described in detail in ref. (1). F rom an angular acceptance of 0.6 msr (15 mrad in the kinematic plane) and a suitable energy resolution of about 20 MeV (FW) for the telescope alone it results an all-over energy resolution for the pr imary photons of about 20 !VfeV (FWHY[), if the energy loss in the liquidhydrogen target (~ 60 m) is taken into account. The second arm dete(ts the photons by a lead-scintillator sandwich counter loaded with 10 radiation lengths of lead. Charged particles are vetoed by counter Z A . The solid angle defined by the lead collimator (20 msr) is as small as is necessary to accept all Compton photons but to reject more than 90% of the 7:~ photons. In order