Hard Exclusive Pion Leptoproduction

Abstract

In this talk it is reported on an analysis of hard exclusive leptoproduction of pions within the handbag approach. It is argued that recent measurements of this process performed by HERMES and CLAS clearly indicate the occurrence of strong contributions from transversely polarized photons. Within the handbag approach such γ * T → π transitions are described by the transversity GPDs accompanied by twist-3 pion wave functions. It is shown that the handbag approach leads to results on cross sections and single-spin asymmetries in fair agreement with experiment. Predictions for other pseudoscalar meson channels are also briefly discussed.

Target and Double Spin Asymmetries of Deeply Virtual $π^0$ Production with a Longitudinally Polarized Proton Target and CLAS

“…Additionally, and perhaps more importantly, the double spin asymmetry measurements provide an independent test of the existing GPDs models probing the underlying assumption of H T and ĒT dominance. The first approach to combine A const LL term with σ 0 and σ T T previously measured by CLAS was conducted in [24]. The constant term was calculated within GK model framework using the H T and ĒT convolutions extracted from unpolarized cross section measurements [11,12] and compared to the measurements presented in this work.…”

Progress and Opportunities in Backward angle (u-channel) Physics

“…Under the Colinear Factorization (CF) regime, a parton is emitted from the nucleon, interacts with the incoming virtual-photon, then returns to the nucleon after the interaction [42]. Studies [50,51] have shown that perturbative calculation methods can be used to calculate the scattering process and extract GPDs from data, while preserving the universal description of the hadronic structure in terms of QCD principles. One limitation is that GPD factorization requires t ∼ t min , namely, the process defaults to a fast-meson and slownucleon final state.…”

Exclusive Backward-Angle Omega Meson Electroproduction

“…Studies [31,32] have shown that perturbation calculation methods can be used As introduced previously, the GPDs depend on x, ξ and t. The ω production process through GPDs in the forward-angle (t-channel) and through TDAs in the backward-angle (u-channel) are schematically shown in Figs. 2.9 (a) and (b), respectively.…”

“…The TDA specifically describes the reaction of backward-angle meson production [30], while GPDs are being actively studied through forward-angle meson production [31,32].…”