High-E-T inclusive jet cross sections in photoproduction at HERA

Inclusive jet differential cross sections for the reaction e+p -> e+ + jet + X with quasi-real photons have been measured with the ZEUS detector at HERA. These cross sections are given for the photon-proton centre-of-mass energy interval 134 < W < 277 GeV and jet pseudorapidity in the range −1 < eta(jet) < 2 in the laboratory frame. The results are presented for three cone radii in the eta − phi plane, R = 1:0; 0:7 and 0:5. Measurements of d sigma=d eta(jet) above various jet-transverse-energy thresholds up to 25 GeV and in three ranges of W are presented and compared to next-to-leading order (NLO) QCD calculations. For jets defined with R = 1:0 differences between data and NLO calculations are seen at high eta(jet) and low E(jet)T . The measured cross sections for jets defined with R = 0:7 are well described by the calculations in the entire measured range of eta(jet) and E(jet)T . The inclusive jet cross section for E(jet)T > 21 GeV is consistent with an approximately linear variation with the cone radius R in the range between 0.5 and 1.0, and with NLO calculations.