Measurement of the t Dependence in Exclusive Photoproduction of Υ{hooked} (1S) Mesons at HERA

The exclusive photoproduction reaction γ p → Υ(1S) p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb −1. The measurement covers the kinematic range 60 < W < 220 GeV and Q 2 < 1 GeV 2 , where W is the photon-proton centre-of-mass energy and Q 2 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.) GeV −2. This constitutes the first measurement of the t dependence of the γ p → Υ(1S) p cross section.