Low-energy photo- and electroproduction for physical pions. II. Photoproduction phenomenology and extraction of the quark mass

The background resonance Δ(1230), N*(1520), N*(1470), and N*(1535) pion and axial-vector amplitudes are first calculated in the soft-pion and on-shell configurations, respectively. Then a comparison is made with the usual soft-pion theorems and on-shell low-energy expansions of current algebra as worked out in the previous paper. The agreement is good, and we also deduce a nucleon dipole form-factor axial-vector mass of mA≈1.23 GeV. Finally, an approximate value for the nonstrange current quark mass of ^m=0.64±1.11 μ is extracted from the data.