Neutral-pion photoproduction on the proton with the CLAS detector

Absolute total and differential cross sections of the gammaN --> piN reaction channels may be used to determine partial wave amplitudes and photocouplings for the baryon resonances which decay predominantly into Npi. The aim of the current analysis of the gammap --> ppi(0) channel is to determine absolute differential and total cross sections to a precision of 5% (systematic) over an energy range of 0.4 to 1.8 GeV. In a single hour of running time, the CLAS collects several hundred thousand single-pi(0) events, making this reaction ideal for studying systematic uncertainties in both the CLAS and the photon tagger. Identification of events coming from gammap --> ppi(0) requires only the identification of a proton with correct missing mass. Nearly complete angular distributions can be obtained over most of the energy range, allowing the reliable determination of the total cross section. The evolution of the differential cross section is well reproduced by the SAID partial-wave analysis even up to about 1.7 GeV where there is but modest existing experimental data from this channel to constrain the fit.