Charged pions polarizability measurement at COMPASS

The pion electromagnetic structure can be probed in $\pi^{−}+(A,Z)\rightarrow\pi^{-}+(A,Z)+\gamma$ Compton scattering in inverse kinematics (Primakoff reaction) and described by the electric $(\alpha_{\pi})$ and the magnetic $(\beta_{\pi})$ polarizabilities that depend on the rigidity of pion’s internal structure as a composite particle. Values for pion polarizabilities can be extracted from the comparison of the differential cross section for scattering of point-like pions with the measured cross section. The opportunity to measure pion polarizability via the Primakoff reaction at the COMPASS experiment was studied with $a$ $\pi^{-}$ beam of 190 GeV during pilot run 2004. The obtained results were used for preparation of the new data taking which was performed in 2009.