A Measurement of the Beauty and Charm Production Cross Sections at the ep Collider HERA

Heavy avor production at HERA is dominated by photoproduction where a quasi real photon scatters o a gluon in the proton While open D and hidden J charm have been measured since the rst real evidence of hidden beauty was seen only in The present analysis measures open beauty and charm photoproduction in the kinematic range Q GeV and yJB and uses data taken with the H detector in the years corresponding to an integrated luminosity of L pb The beauty contribution in the event sample is enhanced by requiring at least two jets with ET GeV and at least one muon in the central region of the detector with a transverse momentum p GeV c The muon has to be found within one of the jets Beauty and charm events are separated on a statistical basis using the transverse momentum of the muon p rel relative to its jet axis The measured p rel distribution is tted with a beauty and charm component in addition to a background from light quarks The shapes of the b and c contributions are obtained from the Aroma Monte Carlo simulation The normalization and shape of the background is extracted directly from data using a detailed parameterization of the muon misidenti cation probability The visible open beauty and charm production cross sections are measured in the kinematic range Q GeV yJB p GeV c to be vis ep bbX nb vis ep ccX nb where the rst uncertainty is statistical and the second systematic The visible beauty cross section is signi cantly higher than the expectation of a leading order QCD event generator with parton showers Aroma which amounts to MC vis ep bbX nb The visible charm cross section agrees well with the prediction of Aroma An extrapolation of the visible charm cross section to the full kinematic range results in a total charm production cross section consistent with a measurement based on the reconstruction of D mesons