Partonic Structure of Light Nuclei

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.