Guy Wilkinson

Abstract:

The B0s and B0 mixing frequencies, Δms and Δmd, are measured using a data sample corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in pp collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8 × 106 candidate events are selected of the type B0(s) → D−(s)μ+ (+ anything), where about half are from peaking and combinatorial backgrounds. To determine the B decay times, a correction is required for the momentum carried by missing particles, which is performed using a simulation-based statistical method. Associated production of muons or mesons allows us to tag the initialstate flavour and so to resolve oscillations due to mixing. We obtain Δms = (17.93 ± 0.22 (stat) ± 0.15 (syst)) ps−1, Δmd = (0.503 ± 0.011 (stat) ± 0.013(syst)) ps−1. The hypothesis of no oscillations is rejected by the equivalent of 5.8 standard deviations for B0s and 13.0 standard deviations for B0. This is the first observation of B0s mixing to be made using only semileptonic decays.

Abstract:

Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3fb-1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130GeV to 209GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant W W and Z Z production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in W W production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the branching fraction of W decays to hadrons, B (W → had), and the trilinear gauge-boson self-couplings g1Z, κγ and λγ are determined to be: mW=80.376±0.033GeV ΓW=2.195±0.083GeV B(W→had)=67.41±0.27% g1Z=0.9840+0.018-0.020 κγ=0.982±0.042λγ=-0.022±0.019. © 2013 Elsevier B.V.