Deeply Virtual Compton Scattering and its Beam Charge Asymmetry in e^\pm p Collisions at HERA

TL;DR

This paper reports the first measurement of beam charge asymmetry in deeply virtual Compton scattering at HERA, analyzing e^+ p and e^- p collision data to explore the interference effects and test theoretical models.

Contribution

It presents the first extraction of beam charge asymmetry in DVCS at low Bjorken x, using HERA data to compare with GPD and dipole models.

Findings

Beam charge asymmetry observed and attributed to Bethe-Heitler and DVCS interference.

Differential cross sections measured as functions of Q^2, W, and t.

Exponential t-slope parameters derived for different kinematic bins.

Abstract

A measurement of elastic deeply virtual Compton scattering gamma* p -> gamma p using e^+ p and e^- p collision data recorded with the H1 detector at HERA is presented. The analysed data sample corresponds to an integrated luminosity of 306 pb^-1, almost equally shared between both beam charges. The cross section is measured as a function of the virtuality Q^2 of the exchanged photon and the centre-of-mass energy W of the gamma* p system in the kinematic domain 6.5 < Q^2 < 80 GeV^2, 30 < W < 140 GeV and |t| < 1 GeV^2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q^2 and W values and exponential t-slope parameters are derived. Using e^+ p and e^- p data samples, a beam charge asymmetry is extracted for the first time in the low Bjorken x kinematic domain. The observed asymmetry is attributed to the interference between Bethe-Heitler and deeply virtual Compton scattering processes. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach.