LHCb

Abstract:

The partial decay width of the Z to {Mathematical expression} quark pairs has been measured by the DELPHI detector at LEP. b-hadrons, containing b-quarks, were tagged by leptons with high transverse momentum relative to the hadron or by tracks with large impact parameters to the primary vertex. The ratio of the numbers of events with a single such tag to those with two tags was used to estimate the efficiency of the method and to reduce the systematic uncertainty. Combining all methods, the value: {Mathematical expression} was found, where the third error corresponds to a±8% uncertainty on the {Mathematical expression} production width. A maximum likelihood in to the single and di-lepton distributions gave the branching fraction of the decays of b-quarks to leptons as: {Mathematical expression} © 1995 Springer-Verlag.

Abstract:

Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given. © 1995.

Abstract:

The exclusive production of ρ{variant}0mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range 7 < Q2< 25 GeV2for λ*p centre of mass (c.m.) energies 40 to 130 GeV. The λ*p → ρ{variant}0p cross section exhibits a Q-(4.2±0.8-0.5+1.4)dependence and both longitudinally and transversely polarised ρ{variant}0's are observed. The λ*p → ρ{variant}0p cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low x. © 1995.

Abstract:

Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep → jet + X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies ETjet> 8 GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale ∼ (ETjet)2. A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30% and 80% of the momentum of the pomeron carried by partons is due to hard gluons. © 1995.