Fe b 19 98 High - E T Inclusive Jet Cross Sections in Photoproduction at HERA ZEUS

Inclusive jet differential cross sections for the reaction e+p → e+ + jet + X with quasireal 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 < η < 2 in the laboratory frame. The results are presented for three cone radii in the η − φ plane, R = 1.0, 0.7 and 0.5. Measurements of dσ/dη 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 η and low E T . The measured cross sections for jets defined with R = 0.7 are well described by the calculations in the entire measured range of η and E T . The inclusive jet cross section for E 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. DESY 98-018 February 1998 The ZEUS Collaboration J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R.L. Talaga, R. Yoshida, H. Zhang Argonne National Laboratory, Argonne, IL, USA p