Measurement of Deeply Virtual Compton Scattering at HERA
H1 Collaboration, C. Adloff
TL;DR
The study reports the first elastic DVCS cross-section measurement at HERA for $e^+ p \to e^+ \gamma p$, spanning $2 < Q^2 < 20\,\mathrm{GeV}^2$, $30 < W < 120\,\mathrm{GeV}$ and $|t| < 1\,\mathrm{GeV}^2$, to probe the diffractive QCD dynamics in both perturbative and nonperturbative regimes. The analysis disentangles the DVCS contribution from the Bethe-Heitler background, which is calculable in QED, by subtracting BH from the total cross section since the interference vanishes upon azimuthal averaging. Measured cross sections are compared to QCD-based calculations that incorporate generalized parton distributions (GPDs) and skewed parton distributions (SPDs), providing tests of parton correlations inside the proton. The results supply empirical input to SPD/GPD frameworks and advance understanding of DVCS as a probe of diffractive QCD dynamics at moderate $Q^2$.
Abstract
A measurement is presented of elastic Deeply Virtual Compton Scattering e^+ + p -> e^+ + photon + p at HERA using data taken with the H1 detector. The cross section is measured as a function of the photon virtuality, Q^2, and the invariant mass, W, of the gamma p system, in the kinematic range 2 < Q^2 < 20 GeV^2, 30 < W < 120 GeV and |t| < 1 GeV^2, where t is the squared momentum transfer to the proton. The measurement is compared to QCD based calculations.