Delta Resoanance Pion Electroproduction Multipoles at Low Q^2
Abstract
In order to determine the spatial distribution of the deviation of the nucleon and Delta from spherical symmetry we have been studying the EMR = E2/M1 and CMR =C2/M1 ratios in pion electroproduction of the Delta resonance. This work focuses on the determination of these quantities near Q^2 = 0.12 (GeV/c)^2, which is where the pion cloud contribution is expected to be a maximum. Although there is an increasing large and accurate data set there is not yet sufficient coverage to perform a model independent multipole fit. A systematic analysis has been made by performing fits on the available data using several parameterizations. In addition to resonance amplitdes E_1+, S_1+ and M_1+, free parameters were chosen for combinations of multipoles for S and P pion waves (S_0+, E_0+, M_1, and S_1). Background (Born) amplitudes were taken from models such as MAID. Applying fits with different parametrizations will give us somewhat an idea of model dependence of the fit. We also varified different data sets in order to study the impact of the data to EMR and CMR ratios. Resulting EMRs and CMRs from these various parametrizations were then averaged over and their standard deviations were evaluated as model errors of EMR and CMR, respectively. In this talk, I'll give more details about the fit and discuss about the results.
 Publication:

APS April Meeting Abstracts
 Pub Date:
 April 2003
 Bibcode:
 2003APS..APR.P8009N