Beam Spin Asymmetries in DVCS with CLAS at 4 .8 GeV

TL;DR

This paper presents measurements of beam spin asymmetries in Deeply Virtual Compton Scattering at 4.8 GeV, covering a wide kinematic range, and compares the results with theoretical models to enhance understanding of nucleon structure.

Contribution

First measurement of DVCS beam spin asymmetries over a broad kinematic range at 4.8 GeV using CLAS, with detailed event separation and comparison to theoretical predictions.

Findings

Successful separation of DVCS-BH and π0 events with less than 5% uncertainty.

Extraction of Q^2- and t-dependence of sinφ moments of asymmetry.

Agreement of measured asymmetries with theoretical calculations.

Abstract

We report measurements of the beam spin asymmetry in Deeply Virtual Compton Scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The DVCS beam spin asymmetry has been measured in a wide range of kinematics, 1(GeV/c)$^2$ $<Q^2<2.8$(GeV/c)$^2$, $0.12<x_B<0.48$, and 0.1 (GeV/c)$^2$ $<-t<0.8$(GeV/c)$^2$, using the reaction \pEpX. The number of H$(e,e^{\prime}\gamma p)$ and H$(e,e^{\prime}\pi^0 p)$ events are separated in each $(Q^2,x_B,t)$ bin by a fit to the line shape of the H$(e,e^{\prime}p)X$ $M_x^2$ distribution. The validity of the method was studied in detail using experimental and simulated data. It was shown, that with the achieved missing mass squared resolution and the available statistics, the separation of DVCS-BH and $\pi^0$ events can reliably be done with less than 5% uncertainty. The $Q^2$- and $t$-dependences of the $\sin\phi$ moments of the asymmetry are extracted and compared with theoretical calculations.