First Measurement of Hard Exclusive p- ? plus plus Electroproduction Beam-Spin Asymmetries off the Proton

The polarized cross-section ratio rrLT �/rr0 from hard exclusive ir-A++ electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV/10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV2 up to 7 GeV2. The reaction provides a novel access to the d-quark content of the nucleon and to p & RARR; A++ transition generalized parton distributions. A comparison to existing results for hard exclusive ir+n and ir0p electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry.

Automated summary

We extracted the polarized cross-section ratio rrLT �/rr0 from hard exclusive ir-A++ electroproduction off an unpolarized hydrogen target using beam-spin asymmetry measurements. This study observed this channel for the first time in the deep-inelastic regime, focusing on very forward-pion kinematics in the valence regime. The reaction provides a unique access to the d-quark content of the nucleon and p & RARR; A++ transition generalized parton distributions.