Deeply virtual Compton scattering off Helium nuclei with positron beams

Abstract

Positron initiated deeply virtual Compton scattering (DVCS) off $$^4$$\n \n \n 4\n \n He and $$^3$$\n \n \n 3\n \n He nuclei is described. The way the so-called $$d-$$\n \n d\n -\n \n 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 $$^3$$\n \n \n 3\n \n 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 $$^3$$\n \n \n 3\n \n He and $$^4$$\n \n \n 4\n \n He are also estimated, at JLab kinematics and, for $$^4$$\n \n \n 4\n \n 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.