Pion Polarizabilities

Abstract

Recent experimental pion polarizability data are reviewed and analyzed. Data on the radiative π^+ meson photoproduction on the proton at MAMI has been used to determine the difference of the electric and magnetic dipole polarizabilities of the charged pion. Fits of the experimental data to the total cross sections of the processes γγ->π^0π^0 and γγ->π^\pmπ^\pm in the energy region from threshold to 2250 MeV and 2500 MeV, respectively, have been carried out using dispersion relations with subtractions for the invariant helicity amplitudes, where the dipole and the quadrupole polarizabilities of π^0 and π^\pm are free parameters. These fits have allowed ones to find the sum and the difference of the electric and magnetic dipole and quadrupole polarizabilities of the pions. These data are compared with the dispersion sum rules and ChPT calculations. The value of the difference of the charged pion dipole polarizabilities found from the fit is in a good agreement with the results obtained at MAMI (2005), in Serpukhov (1983) and Lebedev Physical Institute (1984). However, all these values deviate from the recent calculations in the framework of ChPT.