Measurement of elastic J/ψ photoproduction at HERA
/ Authors
M. Derrick, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. Talaga, R. Yoshida, H. Zhang, G. Bruni
and 27 more authors
G. Romeo, G. Castellini, L. Cifarelli, F. Cindolo, S. Pasquale, I. Gialas, Federico Palmonari, A. Pesci, A. Polini, G. Sartorelli, Y. Garcia, A. Zichichi, L. Feld, M. Pfeiffer, C. Rembser, J. Stamm, R. Wedemeyer, S. Ritz, M. Löwe, J. Mainusch, T. Monteiro, J. Ng, K. Ohrenberg, I. Park, W. Schulz, T. Voss, U. Wollmer
/ Abstract
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 Q2 of 5 × 10−5 GeV2. 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 α Wδ 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 GeV2 where t is the square of the four-momentum exchanged at the proton vertex. dσ/d ¦t¦falls exponentially with a slope parameter of $4.6pm 0.4_{-0.6}^{+0.4} {⤪ GeV}^{-2}$. The measured decay angular distributions are consistent with s-channel helicity conservation.
Journal: Zeitschrift für Physik C Particles and Fields