Pion polarizabities
Murray Moinester (Tel Aviv)

The electric απ and magnetic βπ charged pion polarizabilities characterize the induced dipole moments of the pion during γπ Compton scattering. Pion polarizabilities affect the shape of the γπ Compton scattering angular distribution. By crossing symmetry, the γπ→γπ amplitudes are related to the γγ→ππ amplitudes. Dispersion relations (DR) describe how charged pion polarizabilities contribute to both γγ → π+π- and γγ → π0π0 reactions. A stringent test of chiral perturbation theory (ChPT) is possible by comparing the experimental polarizabilities with ChPT predictions. The combination (απ-βπ) has been measured by: (1) radiative pion Primakoff scattering πZ → πZγ at CERN COMPASS, (2) two-photon pion pair production γγ→ππ at SLAC PEP Mark-II, (3) radiative pion photoproduction γp→ γπn at Mainz MAMI. COMPASS and Mark-II (but not Mainz) polarizabilities are in good agreement with ChPT predictions; and by DRs, with DESY Crystal Ball γγ → π0π0 data. A pion polarizability status report is presented, following the review by S. Scherer and M. Moinester for IJMPA.