Jacek Ciborowski (University of Warsaw)
The exclusive photoproduction reaction gamma p -> Upsilon(1S) p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468pb-1. The measurement covers the kinematic range 60 < W < 220 GeV and Q2 < 1 GeV2, where W is the photon--proton centre-of-mass energy and Q2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured, yielding b=4.3 +2.0-1.3 (stat.) +0.5-0.6 (syst.) GeV2. This constitutes the first measurement of the t dependence of the gamma p -> Upsilon(1S) p cross section.
Olaf Behnke (DESY)