Study of the axial anomaly in the (gamma-proton going to charged-pion neutral-pion neutron) reaction at low t using the clas and the photon tagger
While the agreement between theory and experiment is excellent for the π 0 → 2γ reaction, other reactions that proceed through the axial anomaly have been poorly tested. For example the existing measurement of the γ → 3π amplitude, F3π, is in poor agreement with theory. In the limit of low s and t, the γp → π+π 0n reaction is sensitive to F 3π. In this thesis preliminary cross sections for the γp → π +π0n reaction are presented using the CLAS with tagged photon energies between 1 and 2 GeV and over a range in s and t up to 1 GeV2. The π+ was detected using the time-of-flight and tracking systems. The π0 was detected via reconstruction of the invariant mass of its two decay photons, which were detected by an electromagnetic calorimeter. The presence of the neutron was inferred via missing mass. The sensitivity of these cross sections to F3π in the low t region is studied for s = [special characters omitted] and s = [special characters omitted] at Eγ = 2 GeV. The results show a momentum dependence of the F3π and are consistent with a calculation that includes the effects of ππ final state interactions on the chiral perturbation prediction for F 3π.