Partonic Structure of Light Nuclei

TL;DR

This paper proposes studying the partonic structure of the $^4$He nucleus through exclusive scattering experiments to understand quark and gluon distributions, leveraging the CLAS12 and ALERT detectors.

Contribution

It introduces a novel experimental approach to probe the quark and gluon spatial distributions in $^4$He using coherent DVCS and DVMP measurements.

Findings

Potential to map transverse spatial quark distributions in $^4$He.

Extraction of gluon density profiles within the nucleus.

Insights into threshold effects in $$ production.

Abstract

We propose to study the partonic structure of $^4$He by measuring the Beam Spin Asymmetry (BSA) in coherent Deeply Virtual Compton Scattering (DVCS) and the differential cross-section of the Deeply Virtual Meson Production (DVMP) of the $\phi$. Despite its simple structure, a light nucleus such as $^4$He has a density and a binding energy comparable to that of heavier nuclei. Therefore, by studying $^4$He nucleus, one can learn typical features of the partonic structure of atomic nuclei. The combination of CLAS12 and the ALERT detector provides a unique opportunity to study both the quark and gluon structure of a dense light nucleus. Coherent exclusive DVCS off $^4$He will probe the transverse spatial distribution of quarks in the nucleus as a function of the quarks' longitudinal momentum fraction, $x$. In parallel, the average spatial transverse gluon density of the $^4$He nucleus will be extracted within a GPD framework using the measured longitudinal cross-section for coherent $\phi$ production in a similar range of $x$. Additionally, threshold effects of $\phi$ production can be explored by exploiting the ALERT detector's large acceptance for low $|t|$ events.