Measurement of the t dependence in exclusive photoproduction of gamma(1s) mesons at HERA

Abstract The exclusive photoproduction reaction γ p → ϒ ( 1 S ) 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 − 1.3 + 2.0 ( stat . ) − 0.6 + 0.5 ( syst . ) GeV − 2 . This constitutes the first measurement of the t dependence of the γ p → ϒ ( 1 S ) p cross section.