Beam spin asymmetries in deeply virtual Compton scattering (DVCS) with CLAS at 4.8 GeV

Le résumé fourni par la source

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, $1.0<{Q}^{2}<2.8$ (GeV/$c$)${}^{2}$, $0.12<{x}_{B}<0.48$, and $0.1<\ensuremath{-}t<0.8$ (GeV/$c$)${}^{2}$, using the reaction $\stackrel{\ensuremath{\rightarrow}}{e}p\ensuremath{\rightarrow}{e}^{'}\mathit{pX}$. The number of $\mathrm{H}(e,{e}^{'}\ensuremath{\gamma}p)$ and $\mathrm{H}(e,{e}^{'}{\ensuremath{\pi}}^{0}p)$ events are separated in each $({Q}^{2},{x}_{B},t)$ bin by a fit to the line shape of the $\mathrm{H}(e,{e}^{'}p)X$ ${M}_{x}^{2}$ 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--Bethe-Heitler and ${\ensuremath{\pi}}^{0}$ events can reliably be done with less than 5% uncertainty. Also, the ${Q}^{2}$ and $t$ dependences of the $\mathrm{sin}\ensuremath{\phi}$ moments of the asymmetry are extracted and compared with theoretical calculations.

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