Measurement of exclusive π0 electroproduction structure functions and their relationship to transverse generalized parton distributions

Abstract

Exclusive π⁰ 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 Q², xB, t, and φ, in the Q² range from 1.0 to 4.6 GeV², t up to 2 GeV², and xB from 0.1 to 0.58. Structure functions σT+L, σTT, and σLT 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 σT+L and fails to account for σTT and σLT, 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 π⁰ electroproduction offers direct experimental access to the transversity GPDs.