Measurement of Exclusive pi(0) Electroproduction Structure Functions and their Relationship to Transverse Generalized Parton Distributions

Abstract

Exclusive pi0 electroproduction at a beam energy of 5.75 GeV has been measured with the JeffersonLab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in Q2, xB, t in the Q2 range from 1.0 to 4:6 GeV2, up to 2 GeV2 , and xB from 0.1 to 0.58. Structure functions TþL,TT, and LT were extracted as functions of t for each of 17 combinations of Q2 and xB. The data were compared directly with two handbag-based calculations including both longitudinal and transversity generalized parton distributions (GPDs). Inclusion of only longitudinal GPDs very strongly underestimates TþL and fails to account for TT and LT, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity-flip and helicity nonflip processes. The results confirm that exclusive p0 electroproduction offers direct experimental access to the transversity GPDs