Dresden 2000 – scientific programme
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T: Teilchenphysik
T 601: QCD 6
T 601.7: Talk
Friday, March 24, 2000, 15:45–16:00, H\,01
Photon Structure via DiJet Production at HERA — •Dorian Kçira — ZEUS/DESY, Notkestr.85, D-22603 Hamburg
We present a study of the dependence of the photon structure on the photon virtuality, Q2, by measuring the reaction e+ + P → e+ + jet + jet + X with the ZEUS detector at HERA. Samples of dijet events in the Q2 ranges 1.5−4.5 GeV2, 0.10−0.55 GeV2, and Q2 ≃ 0 GeV2 with inelasticity, y, between 0.2 and 0.55 have been selected using the cone and KT jet finder algorithms. Results are presented of the dijet cross-sections with asymmetric cuts on the jet transverse energy of each jet ( Etjet1 > 7.5 GeV, Etjet2 > 6.5 GeV). The production of dijet events as a function of the fraction of the photon momentum participating in the hard process, xγobs, and Q2, has been measured and compared with leading-logarithm parton-shower Monte Carlo calculations using different photon parton distribution functions. The ratio of the measured dijet cross-sections of resolved-enriched ( xγobs < 0.75) and direct-enriched ( xγobs > 0.75) events is found to decrease with increasing photon virtuality.