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

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.