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

Exclusive pi(0) electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in Q(2), x(B), t, and phi(pi), in the Q(2) range from 1.0 to 4.6 GeV2, -t up to 2 GeV2, and x(B) from 0.1 to 0.58. Structure functions sigma(T) + epsilon sigma(L), sigma(TT), and sigma(LT) were extracted as functions of t for each of 17 combinations of Q(2) and x(B). 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 sigma(T) + epsilon sigma(L) and fails to account for sigma(TT) and sigma(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 pi(0) electroproduction offers direct experimental access to the transversity GPDs.