W. Armstrong, et al. (ALERT Collaboration)
Jefferson PAC Proposal PR12-17-012 (2017)
Publication year: 2017

We propose to study the partonic structure of 4He 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 ϕ. Despite its simple structure, a light nucleus such as 4He has a density and a binding energy comparable to that of heavier nuclei. Therefore, by studying 4He 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 4He 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 4He nucleus will be extracted within a GPD framework using the measured longitudinal cross-section for coherent ϕ production in a similar range of x. Additionally, threshold effects of ϕproduction can be explored by exploiting the ALERT detector’s large acceptance for low |t| events.

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