Measurement of elastic ϒ photoproduction at HERA

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 43.2pb−1. The ϒ meson has been observed in photoproduction for the first time. The sum of the products of the elastic ϒ(1S),ϒ(2S),ϒ(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.