Beauty-Mesons

For the first time, the production cross section for B-mesons, these are particles with a heavy beauty-quark, was measured in lepton-proton collisions. Semi- leptonic decays of the B-mesons were analysed: beauty -> charm muon neutrino. The main observable is the transverse momentum of the muon relative to the beauty-quark jet: owing to its large mass, the charm quark direction of flight reflects the direction of the beauty-quark. In contrast, the muon can be found at large angles relative to the direction of the beauty quark.

The B-meson cross section was determined using a simultaneous fit to the measured distribution of the relative transverse momentum of the muon together with the light quark and the charm quark contributions. In the observed kinematic region, the cross section was determined to be sigma (e p-> b anti-b X) = (0.93+-0.08(stat)+0.21-0.12) nb.  The measured cross section is larger by a factor of 5 than expected from a leading order QCD calculation which challenges explanation.