FIZIKA B 17 (2008) 2, 313 - 320



on behalf of the COMPASS collaboration

Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems, Dubna, Russia
E-mail address:

Received 23 October 2007;  Accepted 20 February 2008
Online 20 June 2008

The electromagnetic structure of pions is probed in p-+(A,Z) p-+(A,Z)+g Compton scattering in inverse kinematics (Primakoff reaction) and described by the electric ([`(ap)]) and the magnetic ([`(bp)]) 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 pointlike pions with the measured cross section. The pion polarizability measurement was performed with a p- beam of 190 GeV. The high beam intensity, the good spectrometer resolution, the high rate capability, the high acceptance and the possibility to use pion and muon beams, unique to the COMPASS experiment, provide the tools to measure precisely the pion polarizabilities in the Primakoff reaction. The preliminary result for pion polarizabilities under the assumption of [`(ap)]+[`(bp)]=0 is [`(ap)]=-[`(bp)] = (2.51.7stat0.6syst)10-4 fm3.

PACS numbers: 25.80.Ek, 13.60.Fz
UDC 539.126

Keywords: pion, electromagnetic structure, polarizability, Compton scattering, Primakoff reaction

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