Measurement of elastic Upsilon photoproduction at HERA

The photoproduction reaction gamma p -> mu+ mu- p has been studied in ep interactions using the ZEUS detector at HERA. The data sample corresponds to an integrated luminosity of 43.2 pb^{-1}. The Upsilon meson has been observed in photoproduction for the first time. The sum of the products of the elastic Upsilon(1S), Upsilon(2S), Upsilon(3S) photoproduction cross sections with their respective branching ratios is determined to be 13.3 +- 6.0(stat.)^{+2.7}_{-2.3}(syst.) pb at a mean photon-proton centre of mass energy of 120 GeV. The cross section is above the prediction of a perturbative QCD model.

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13 pages including 3 figures Report-no: DESY-98-089

positron p: colliding beams
exchange: one-photon
photon p: exclusive reaction
upsilon mesons: photoproduction
upsilon mesons: leptonic decay
mass spectrum: (muon+ muon-)
channel cross section: branching ratio
energy dependence
ZEUS
experimental results

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Figures(4)

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