A multidimensional study of the structure function ratio $\sigma_{LT'}/\sigma_{0}$ from hard exclusive $\pi^+$ electro-production off protons in the GPD regime

TL;DR

This study measures the ratio of structure functions in exclusive pion electro-production off protons, revealing insights into nucleon GPDs and tensor charge, with results favoring Regge models at low Q² and GPD models at high Q².

Contribution

It provides the first multidimensional extraction of the structure function ratio $\sigma_{LT'}/\sigma_{0}$ in a wide kinematic range, testing GPD and Regge models against experimental data.

Findings

Regge model better describes low Q² data

GPD model more accurate at high Q²

Results sensitive to chiral-odd GPDs and tensor charge

Abstract

A multidimensional extraction of the structure function ratio $\sigma_{LT'}/\sigma_{0}$ from the hard exclusive $\vec{e} p \to e^\prime n \pi^+$ reaction above the resonance region has been performed. The study was done based on beam-spin asymmetry measurements using a 10.6 GeV incident electron beam on a liquid-hydrogen target and the CLAS12 spectrometer at Jefferson Lab. The measurements focus on the very forward regime ($t/Q^{2}$ $\ll$ 1) with a wide kinematic range of $x_{B}$ in the valence regime (0.17 $<$ $x_{B}$ $<$ 0.55), and virtualities $Q^{2}$ ranging from 1.5 GeV$^{2}$ up to 6 GeV$^{2}$. The results and their comparison to theoretical models based on Generalized Parton Distributions demonstrate the sensitivity to chiral-odd GPDs and the directly related tensor charge of the nucleon. In addition, the data is compared to an extension of a Regge formalism at high photon virtualities. It was found that the Regge model provides a better description at low $Q^{2}$, while the GPD model is more appropriate at high $Q^{2}$.