The Q^2 Dependence of Dijet Cross Sections in gamma p Interactions at HERA

Abstract

The dependence of the photon structure on the photon virtuality, Q^2, is studied by measuring the reaction e^+p\to e^+ + {\rm jet} + {\rm jet} + {\rm X} at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected in the Q^2 ranges \approx 0 GeV^2, 0.1-0.55 GeV^2, and 1.5-4.5 GeV^2, having two jets with transverse energy E_T^{jet} > 5.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, x_gamma. The ratio of the dijet cross section with x_gamma < 0.75 to that with x_gamma > 0.75 decreases as Q^2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can be interpreted in terms of a resolved photon component that falls with Q^2 but remains present at values of Q^2 up to 4.5 GeV^2. However, none of the models considered gives a good description of the data.

15 pages and 4 figures

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Cited by in corpus (14)

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• Collider Physics at HERA
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• Survey of present data on photon structure functions and resolved photon processes
• Production of D* Mesons with Dijets in Deep-Inelastic Scattering at HERA
• Electroproduction Cross Section of Large_Et Hadrons at NLO and Virtual Photon Structure Function
• High Energy Photoproduction
• The dependence of dijet production on photon virtuality in ep collisions at HERA
• Deep inelastic scattering and forward neutral pion production at NLO
• Measurement of lepton-jet correlation in deep-inelastic scattering with the H1 detector using machine learning for unfolding
• Low-x Physics
• A two-component model for ${\gamma }^{\ast }$-p scattering at small Bjorken x
• Resolved photon and multi-component model for ${\gamma }^{\ast }$p and ${\gamma }^{\ast }{\gamma }^{\ast }$ scattering at high energies