LHCb

Abstract:

DØ has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb^-1 of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pp̄ collisions at √s=1.8 TeV are σWB(W→eν)=2.36±0.02±0.08±0.13 nb, σWB(W →μν)=2.09±0.06±0.22±0.11 nb, σZB(Z→e⁺e ^-)=0.218±0.008±0.008±0.012 nb, and σZB(Z →μ⁺μ ^-)=0.178±0.022±0.021±0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find σWB(W→lν)/σZB(Z→l ⁺l^-)=10.90±0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Γ(W)=2.044±0.097 GeV. ©1999 The American Physical Society.

Abstract:

Beam tests were performed in 1998 to investigate the performance of a prototype of the downstream RICH of the LHCb using hybrid photo-diodes and multi anode PMTs. The angular resolutions obtained from these photodetectors under various experimental configurations are compared with the expectations from simulation. (C) 1999 Elsevier Science B.V. All rights reserved.

Abstract:

Beam tests were performed to investigate the performance of a prototype of the downstream ring imaging counter (RICH) of the LHCb using hybrid photodiodes and multi-anode photomultipliers. The Cerenkov angle resolution obtained for the three types of photodetectors tested agreed well with the expectations from simulations. Using 61-pixel hybrid photodiodes, a single photon resolution of 0.35 mrad was attained and the particle identification capability was demonstrated.

Abstract:

The partial decay width of the Z to bb̄ quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays of b-hadrons were tagged by several methods using tracks with large impact parameters and/or reconstructed secondary vertices, complemented by event shape variables. Combining these methods in a multivariate analysis the value Γ(Z → bb̄)/Γ(Z → had) = 0.21634 ± 0.00067 (stat) ± 0.00060 (syst) was obtained, where the cc̄ production fraction was fixed to its Standard Model value.

Abstract:

Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field. © 1999 Elsevier Science B.V. All rights reserved.