Measurement of elastic ϒ photoproduction at HERA

Abstract The photoproduction reaction γp→ μ + μ − 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 ϒ meson has been observed in photoproduction for the first time. The sum of the products of the elastic ϒ (1 S ), ϒ (2 S ), ϒ (3 S ) 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.