A high angular-resolution and time-of-flight detector system for recoil protons from the reactions p(γ, γ)p and p(γ, π0)p

Using the Mainz NaI(Tl)BaF2 photon spectrometer CATS (Compton And Two photon Spectrometer) together with the prototype of a universal spectrometer for recoil protons TRAJAN (TRAjectory ANalyser) we have studied different methods to disentangle Compton scattering by the proton from the large π0 background through the energy range of the Δ resonance. CATS is a modular 48 cm ⊘ × 64 cm NaI(Tl) detector with an energy resolution of 1.5% combined with a 2π array of 61 BaF2 detectors. TRAJAN consists of a hodoscope with two planes, a wire chamber with horizontal and vertical wires and a grid of horizontal and vertical plastic scintillator strips, followed by a wall of nine NaI(Tl) detectors. By this arrangement the proton energy was obtained via a time-of-flight analysis and the recoil angle of the protons via a trajectory reconstruction. Additionally, a ΔE-E analysis of the detected particles allows us to suppress the electromagnetic background. By reconstructing the proton trajectory the segment of the scattering target can be determined where the Compton scattering process or the π0 production process had taken place. In this way it is possible to correct the event distributions for the smearing-out caused by the finite target length and thus to improve on the separation of the two types of events.