Measurement of Elastic J/ψ Photoproduction at HERA
نویسندگان
چکیده
The reaction γ p → J/ψ p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/ψ photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q of 5 × 10−5 GeV. The photoproduction cross section, σγp→J/ψp, is observed to rise steeply with W . A fit to the data presented in this paper to determine the parameter δ in the form σγp→J/ψp ∝W δ yields the value δ = 0.92±0.14±0.10. The differential cross section dσ/d|t| is presented over the range |t| < 1.0 GeV where t is the square of the fourmomentum exchanged at the proton vertex. dσ/d|t| falls exponentially with a slope parameter of 4.6 ± 0.4 −0.6 GeV −2. The measured decay angular distributions are consistent with s-channel helicity conservation. 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, 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, L. Feld, M. Grothe, H. Hartmann, K. Heinloth, L. Heinz, E. Hilger, H.-P. Jakob, U.F. Katz, E. Paul, M. Pfeiffer, Ch. Rembser, J. Stamm, R. Wedemeyer 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, 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, 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, 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. 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
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