A Study of Pion Photoproduction on Helium-4 in the Delta Resonance Region using Polarised and Unpolarised Photons
Arneil, Jason F
Measurements of the reaction on a 4 He target have been carried out using both unpolarised and polarised photons. This work is the latest in a series of experiments conducted by the Edinburgh University Nuclear Physics group in collaboration with the Universities of Glasgow and Tubingen. The experiment was carried out using the 855 MeV MAMIB electron accelerator at the Institut fur Kernphysik, Mainz, between March and August of 1996. The 855 MeV electrons from the accelerator were directed either, on to a 4 micron Nickel foil to produce unpolarised photons or on to a 0.1 mm Diamond to produce polarised photons. These photons were then tagged with a resolution of 2 MeV using a spectrometer. The photons then impinged on a 4 He cryotarget. Two sets of detectors were used to detect the reaction products. PiP, a plastic scintillator hodoscope, was used to detect the positive pions; and TOF a time of flight array, was used to detect the neutrons. Data was analysed for unpolarised photon energy regions centred at E =260,300,340 and 380 MeV and two polarised regions centred at E =258 and 338 MeV. The unpolarised data is presented as double and triple differential cross sec tions while the polarised data is presented as photon asymmetries of the corres ponding double differential cross section. A comparison is made with Plane Wave Impulse Approximation (PWIA) calculations by Louis Wright, both with and without final state interaction corrections. It is concluded that for the unpolar ised data a more sophisticated treatment of the final state interactions is required while for the polarised data reasonable agreement is found between experiment and theory.