Measurement of Deeply Virtual Compton Scattering at HERA
H1 Collaboration
TL;DR
Deeply Virtual Compton Scattering (DVCS) on the proton is studied as a clean probe of Generalised Parton Distributions (GPDs), encoding correlations and transverse parton structure beyond conventional PDFs. The paper reports the first elastic DVCS cross-section measurements in $e^+ p$ collisions with the H1 detector at HERA, using $46.5~\mathrm{pb}^{-1}$ of data. Cross sections are presented as functions of $Q^2$, $W$, and, for the first time, the differential distribution in $|t|$ within $2< Q^2< 80~\mathrm{GeV}^2$, $30< W< 140~\mathrm{GeV}$ and $|t|<1~\mathrm{GeV}^2$. The measurements are described by next-to-leading order QCD calculations based on GPDs as well as by color dipole model predictions, supporting the applicability of DVCS to constrain GPDs at HERA. The differential in $t$ provides direct access to the transverse spatial distribution of partons and helps test the factorization framework for DVCS.
Abstract
A measurement is presented of elastic deeply virtual Compton scattering γ* p \to γp made using e^+ p collision data corresponding to a luminosity of 46.5 pb^{-1}, taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q^2, the invariant mass of the γ* p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range 2 < Q^2 < 80 GeV^2, 30 < W < 140 GeV and |t| < 1 GeV^2. QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.