Measurement of the transverse target-spin asymmetry associated with deeply virtual Compton scattering on the proton

TL;DR

This paper reports measurements of the transverse target-spin asymmetry in deeply virtual Compton scattering on the proton, providing data that supports GPD-based models and offers insights into the u-quark angular momentum.

Contribution

First measurement of TTSA in DVCS on the proton using polarized targets, testing GPD models and constraining quark angular momentum.

Findings

TTSA amplitudes measured as functions of -t, x_B, Q^2

Results agree with GPD-based theoretical predictions

Data can help constrain u-quark angular momentum in the nucleon

Abstract

Measurements of deeply virtual Compton scattering (DVCS) made at HERMES using 27.6 GeV $e^\pm$ beams and various internal polarized or unpolarized gaseous targets are discussed. Results are reported on the transverse target-spin asymmetry (TTSA) associated with DVCS, extracted from data accumulated in 2002-2004 with the $e^+$ beam on a transversely polarized hydrogen target. TTSA amplitudes leading in twist and $\alpha_S$ are given as a function of $-t$, $x_B$ and $Q^2$ in the kinematic range $|t|<0.7$ GeV$^2$, $0.03<x_B<0.35$ and $1<Q^2<10$ GeV$^2$. Theoretical predictions based on a phenomenological model of generalized parton distributions (GPDs) agree with the experimental results. With additional statistics accumulated in 2005, one may constrain the $u$-quark total angular momentum in the nucleon within this model.