Deeply virtual Compton scattering off Helium nuclei with positron beams

TL;DR

This paper explores positron-induced deeply virtual Compton scattering off helium nuclei, emphasizing the measurement of the $d$-term and the potential of positron beams to probe higher-twist effects in nuclear GPDs.

Contribution

It introduces a novel approach to measure the $d$-term using positron beams in DVCS off helium nuclei and discusses the advantages of this method for future experiments.

Findings

Unpolarized beam charge asymmetries estimated at JLab and EIC kinematics.

Potential to extract the $d$-term from real part of Compton form factor.

Positron beams enable investigation of higher-twist effects in nuclear GPDs.

Abstract

Positron initiated deeply virtual Compton scattering (DVCS) off $^4$He and $^3$He nuclei is described. The way the so-called $d-$term could be obtained from the real part of the relevant Compton form factor is summarized, and the importance and novelty of this measurement is discussed. The measurements addressed for $^3$He targets could be very useful even in a standard unpolarized target setup, measuring beam spin and beam charge asymmetries only. The unpolarized beam charge asymmetries for DVCS off $^3$He and $^4$He are also estimated, at JLab kinematics and, for $^4$He, also at a configuration typical at the future Electron-Ion Collider. Incoherent DVCS processes, in particular the ones with tagging the internal target by measuring slow recoiling nuclei, and the unique possibility offered by positron beams for the investigation of Compton form factors of higher twist, are also briefly addressed.