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T: Teilchenphysik

T 303: Photonstruktur I

T 303.4: Talk

Tuesday, March 24, 1998, 17:25–17:40, HS C

Dijet Cross Sections in γ−P Interactions using Real and Virtual Photons at HERA — •Dorian Kçira — Hamburg University

We present a study of the dependence of the photon structure on the photon virtuality, Q², using electroproduced dijet events measured with the ZEUS detector at HERA. Samples of events from photons of virtuality in the ranges of 0.1 < Q² < 0.70 GeV² and Q² ≈ 0.0 GeV² having two jets of transverse energy E_T^jet > 6.5 GeV and pseudorapidity -1.125 < η < 1.875 in the final state have been selected. The uncorrected rates of dijets as a function of Q² and of the fraction of the photon momentum, which participate in the hard process, are compared with predictions of the HERWIG Monte Carlo. The presence of a resolved component is demonstrated up to Q² ≈ 0.7 GeV². The ratio of resolved over direct dijet cross sections is measured as a function of Q² up to a Q²= 0.55 GeV². This ratio decreases with increasing photon virtuality.