Study of the Axial Anomaly using the γp → π<sup>+</sup>Pπ<sup>0</sup> n Reaction Near Threshold

Abstract

This experiment was one of the first photoproduction experiments performed at Jefferson Lab using the CLAS and the Photon Tagger. The event reconstruction and the photon flux determination procedures have been developed and were proven to work well as we can see from the cross section measurement of the γp → π+n reaction. The preliminary results at CLAS for this reaction agree very well with previous world data. The analysis procedure has been developed to analyze the double-pion photoproduction. The differential cross sections for the γp → Pπ+π0n reaction have been measured with incident photon energies between 1 and 2 GeV. The Chew-Low extrapolation technique was used to extract the associated γπ → ππ cross sections from the differential cross sections. The extrapolation procedure of extracting the pole cross section has been explored. F3π was obtained from the γπ → ππ cross sections. The results show a momentum dependence of the F3π amplitude in which they agree with Holstein's calculation. These measurements test fundamental predictions of low energies QCD. Future work on this analysis will help reduce the uncertainty in F3π, and extend the measurements to the lower and higher s regions.