Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
Letter
Postuma, AC, Huber, GM, Gaskell, DJ et al. (2026). Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
. Physics Letters B, 872 10.1016/j.physletb.2025.140094
Postuma, AC, Huber, GM, Gaskell, DJ et al. (2026). Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
. Physics Letters B, 872 10.1016/j.physletb.2025.140094
Deep exclusive meson production (DEMP) reactions, such as p(e→,e′π+)n, provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive p(e→,e′π+)n reaction, as measured in the KaonLT experiment at Jefferson Lab Hall C. A 10.6 GeV longitudinally polarized electron beam was incident on an unpolarized liquid hydrogen target, and the scattered electron and produced meson were detected in two magnetic focusing spectrometers, enabling precision cross section measurements. The cross section ratio σLT′/σ0 was extracted from the beam-spin asymmetry ALU . The t -dependence of σLT′/σ0 was determined at fixed Q 2 and xB over a range of kinematics from 2 ' Q 2 ' 6 GeV2 above the resonance region (W ' 2 GeV). Furthermore, these data are combined with recent results from CLAS/CLAS12 to determine the Q 2-dependence of σLT′/σ0 at two (xB, t) settings. This was fairly flat, with Q 2 not having a measurable effect on the value of σLT′/σ0 in the range explored. Results are compared to predictions from the generalized parton distribution (GPD) formalism, which relies explicitly on hard/soft factorization, and Regge formalism. The Regge models better predict σLT′/σ0, which suggests that the factorization regime is not yet reached.
