| Abstract: | 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 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 gamma
p -> Upsilon(1S) p cross section. |
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