Hints on the quadrupole deformation of the (1232)

Abstract

The E2/M1 ratio (EMR) of the (1232) is extracted from the world data in pion photoproduction by means of an effective Lagrangian approach (ELA). This quantity has been derived within a crossing symmetric, gauge invariant, and chiral symmetric Lagrangian model which also contains a consistent modern treatment of the (1232) resonance. The bare s-channel (1232) contribution is well isolated and final state interactions (FSI) areeffectively taken into account fulfilling Watson’s theorem. The obtained EMR value, EMR=(−1.30±0.52)%, is in good agreement with the latest lattice QCD calculations [Phys. Rev. Lett. 94 , 021601 (2005)] and disagrees with results of current quark model calculations.