Search for Quadrupole Strength in the Electro-excitation of the Delta(1232)

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  • 24 February 1999
Abstract
High-precision H(e,e'p)pi0 measurements, focused on the determination of resonant quadrupole amplitudes in the N-Delta transition and the related issue of baryon "deformation," have been made at a central Q2 = 0.126 (GeV/c)2 and an invariant mass range of 170 MeV around the Delta(1232) resonance. None of the available theoretical predictions can simultaneously reproduce the measured coincident cross sections, asymmetries, and responses. Moreover the new data strongly suggest that the non-resonant amplitudes from the interfering processes which, up to now, have been assumed to be negligible, contribute significantly. They thus demonstrate the inadequacy of the previously practiced analysis scheme, the inconsistencies it generates, and the need to investigate the contributions of all coherent small amplitudes before conclusions concerning the issue of baryon deformation could be reached.

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