1 research outputs found
Study of pion photoproduction on helium-4 in the delta resonance region using polarised and unpolarised photons
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