2 v 1 6 O ct 1 99 7 Measurement of Jet Shapes in Photoproduction at HERA ZEUS

The shape of jets produced in quasi-real photon-proton collisions at centre-of-mass energies in the range 134 − 277 GeV has been measured using the hadronic energy flow. The measurement was done with the ZEUS detector at HERA. Jets are identified using a cone algorithm in the η − φ plane with a cone radius of one unit. Measured jet shapes both in inclusive jet and dijet production with transverse energies E T > 14 GeV are presented. The jet shape broadens as the jet pseudorapidity (η) increases and narrows as E jet T increases. In dijet photoproduction, the jet shapes have been measured separately for samples dominated by resolved and by direct processes. Leading-logarithm parton-shower Monte Carlo calculations of resolved and direct processes describe well the measured jet shapes except for the inclusive production of jets with high η and low E T . The observed broadening of the jet shape as η increases is consistent with the predicted increase in the fraction of final state gluon jets. DESY 97-191 October 1997 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 M.C.K. Mattingly Andrews University, Berrien Springs, MI, USA F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, A. Polini, F. Ricci, G. Sartorelli, Y. Zamora Garcia, A. Zichichi University and INFN Bologna, Bologna, Italy f C. Amelung, A. Bornheim, I. Brock, K. Coböken, J. Crittenden, R. Deffner, M. Eckert, M. Grothe, H. Hartmann, K. Heinloth, L. Heinz, E. Hilger, H.-P. Jakob, U.F. Katz, R. Kerger, E. Paul, M. Pfeiffer, Ch. Rembser, J. Stamm, R. Wedemeyer, H. Wieber Physikalisches Institut der Universität Bonn, Bonn, Germany c D.S. Bailey, S. Campbell-Robson, W.N. Cottingham, B. Foster, R. Hall-Wilton, M.E. Hayes, G.P. Heath, H.F. Heath, J.D. McFall, D. Piccioni, D.G. Roff, R.J. Tapper H.H. Wills Physics Laboratory, University of Bristol, Bristol, U.K. o M. Arneodo, R. Ayad, M. Capua, A. Garfagnini, L. Iannotti, M. Schioppa, G. Susinno Calabria University, Physics Dept.and INFN, Cosenza, Italy f J.Y. Kim, J.H. Lee, I.T. Lim, M.Y. Pac Chonnam National University, Kwangju, Korea h A. Caldwell, N. Cartiglia, Z. Jing, W. Liu, B. Mellado, J.A. Parsons, S. Ritz, S. Sampson, F. Sciulli, P.B. Straub, Q. Zhu Columbia University, Nevis Labs., Irvington on Hudson, N.Y., USA q P. Borzemski, J. Chwastowski, A. Eskreys, J. Figiel, K. Klimek, M.B. Przybycień, L. Zawiejski Inst. of Nuclear Physics, Cracow, Poland j L. Adamczyk, B. Bednarek, M. Bukowy, K. Jeleń, D. Kisielewska, T. Kowalski, M. Przybycień, E. Rulikowska-Zarȩbska, L. Suszycki, J. Zaja̧c Faculty of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, Cracow, Poland j Z. Duliński, A. Kotański Jagellonian Univ., Dept. of Physics, Cracow, Poland k G. Abbiendi, L.A.T. Bauerdick, U. Behrens, H. Beier, J.K. Bienlein, G. Cases, O. Deppe, K. Desler, G. Drews, U. Fricke, D.J. Gilkinson, C. Glasman, P. Göttlicher, T. Haas, W. Hain, D. Hasell, K.F. Johnson, M. Kasemann, W. Koch, U. Kötz, H. Kowalski, J. Labs, L. Lindemann, B. Löhr, M. Löwe, O. Mańczak, J. Milewski, T. Monteiro, J.S.T. Ng, D. Notz, K. Ohrenberg, I.H. Park, A. Pellegrino, F. Pelucchi, K. Piotrzkowski, M. Roco, M. Rohde, J. Roldán, J.J. Ryan, A.A. Savin, U. Schneekloth, F. Selonke, B. Surrow, E. Tassi, T. Voß, D. Westphal, G. Wolf, U. Wollmer, C. Youngman, A.F. Żarnecki, W. Zeuner Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany