Coherent deeply virtual Compton scattering off $^4$He

TL;DR

This paper investigates coherent deeply virtual Compton scattering off helium-4 using impulse approximation, deriving a convolution formula for nuclear GPDs, and finds good agreement with recent experimental data, setting the stage for more refined future calculations.

Contribution

It introduces a convolution formula for nuclear GPDs based on a non-diagonal spectral function and applies a realistic nuclear model, advancing the theoretical understanding of helium-4 scattering.

Findings

Good agreement with JLab data.

Reproduces nuclear form factors and parton distributions.

Provides a foundation for refined future calculations.

Abstract

Coherent Deeply virtual Compton scattering off the $^4$He nucleus is studied in impulse approximation. A convolution formula for the nuclear Generalized Parton Distribution (GPD) is derived in terms of the $^4$He non-diagonal spectral function and of the GPD of the struck nucleon. A model of the nuclear non diagonal spectral function, based on the momentum distribution corresponding to the AV18 nucleon-nucleon interaction, is used in the actual calculation. Typical impulse approximation results are reproduced, in proper limits, for the nuclear form factor and for nuclear parton distributions. The nuclear generalized parton distribution and the Compton form factor are evaluated using, as nucleonic ingredient, a well known generalized parton distribution model. An overall very good agreement is found with the data recently published by the EG6 experiment at the Jefferson Laboratory (JLab). More refined nuclear calculations are addressed and will be necessary for the expected improved accuracy of the next generation of experiments at JLab, with the 12 GeV electron beam and high luminosity.