0 v 2 1 1 Se p 19 96 Measurement of Elastic ω Photoproduction at HERA ZEUS

The reaction γp → ωp (ω → π+π−π0 and π0 → γγ) has been studied in ep interactions using the ZEUS detector at photon-proton centre-of-mass energies between 70 and 90GeV and |t| < 0.6GeV, where t is the squared four momentum transferred at the proton vertex. The elastic ω photoproduction cross section has been measured to be σγp→ωp = 1.21 ± 0.12 ± 0.23μb. The differential cross section dσγp→ωp/d|t| has an exponential shape e−b|t| with a slope b = 10.0±1.2±1.3GeV. The angular distributions of the decay pions are consistent with s-channel helicity conservation. When compared to low energy data, the features of ω photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the ρ0 and φ photoproduction cross sections at HERA show a similar behaviour. The ZEUS Collaboration M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J.R. Okrasiński, J. Repond, R. Stanek, R.L. Talaga, 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, P. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, P. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, A. Polini, G. Sartorelli, Y. Zamora Garcia, A. Zichichi University and INFN Bologna, Bologna, Italy f C. Amelung, A. Bornheim, J. Crittenden, R. Deffner, M. Eckert, L. Feld, A. Frey, M. Geerts, M. Grothe, H. Hartmann, K. Heinloth, L. Heinz, E. Hilger, H.-P. Jakob, U.F. Katz, S. Mengel, E. Paul, M. Pfeiffer, Ch. Rembser, D. Schramm, J. Stamm, R. Wedemeyer Physikalisches Institut der Universität Bonn, Bonn, Germany c S. Campbell-Robson, A. Cassidy, W.N. Cottingham, N. Dyce, B. Foster, S. George, M.E. Hayes, G.P. Heath, H.F. Heath, D. Piccioni, D.G. Roff, R.J. Tapper, R. Yoshida 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 A. Caldwell, N. Cartiglia, Z. Jing, W. Liu, J.A. Parsons, S. Ritz, F. Sciulli, P.B. Straub, L. Wai, S. Yang, Q. Zhu Columbia University, Nevis Labs., Irvington on Hudson, N.Y., USA q P. Borzemski, J. Chwastowski, A. Eskreys, Z. Jakubowski, M.B. Przybycień, M. Zachara, L. Zawiejski Inst. of Nuclear Physics, Cracow, Poland j L. Adamczyk, B. Bednarek, K. Jeleń, D. Kisielewska, T. Kowalski, M. Przybycień, E. RulikowskaZarȩbska, 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