Abstract

A measurement of elastic deeply virtual Compton scattering γ∗p→γp 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 Q2 of the exchanged photon and the centre-of-mass energy W of the γ∗p system in the kinematic domain 6.5<Q2<80 GeV2, 30<W<140 GeV and |t|<1 GeV2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q2 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.

Highlights

  • Measurements of the deep-inelastic scattering (DIS) of leptons and nucleons allow the extraction of Parton Distribution Functions (PDFs)

  • In the Bjorken scaling regime, corresponding to large virtuality Q 2 of the exchanged photon and |t|/Q 2 1, where t is the squared momentum transfer at the proton vertex, Quantum Chromodynamic (QCD) calculations assume that the exchange involves two partons in a colourless configuration, having different longitudinal and transverse momenta

  • It is complementary to measurements performed at lower Q 2 using HERA I data [10]. Using both beam charges, the beam charge asymmetry of the interference between the BH and deeply virtual Compton scattering (DVCS) processes is measured for the first time at a collider

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Summary

Collaboration

Mediterranee, Marseille, France v Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico w Departamento de Fisica, CINVESTAV, Mexico x Institute for Theoretical and Experimental Physics, Moscow, Russia y Lebedev Physical Institute, Moscow, Russia z Max-Planck-Institut für Physik, München, Germany aa LAL, Univ. A measurement of elastic deeply virtual Compton scattering γ ∗ p → γ p using e+ p and e− p collision data recorded with the H1 detector at HERA is presented. 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 γ ∗ p system in the kinematic domain 6.5 < Q 2 < 80 GeV2, 30 < W < 140 GeV and |t| < 1 GeV2, where t denotes the squared momentum transfer at the proton vertex. 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. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach

Introduction
Theoretical framework
Experimental conditions and Monte Carlo simulation
Event selection
Cross section and beam charge asymmetry measurements
Cross sections and t-dependence
Inelastic DVCS t-dependence
Beam charge asymmetry
Conclusion
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