Guy Wilkinson

Abstract:

A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D0 → K−K+ is performed using pp collision data, corresponding to an integrated luminosity of 3 fb^−1 , collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D*+ → D0π+ and D*− → D‾0π− decays. The time-integrated CP asymmetry ACP (K−K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D0 → K−π+, D+ → K−π+π+ and D+ → K‾0π+ decays used as calibration channels. It is found to be A CP(K−K+) = (0.14±0.15 (stat)±0.10 (syst))%. A combination of this result with previous LHCb measurements yields A CP (K − K + )=(0.04±0.12 (stat)±0.10 (syst))%,A CP (π−π+) = (0.07±0.14 (stat)±0.11 (syst))%. These are the most precise measurements from a single experiment. The result for A CP(K−K+) is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

Abstract:

Measurements of the cross section for producing b quarks in the reaction pp→bb[over ¯]X are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity η in the range 2<η<5 covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of b-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross sections in the covered η range are 72.0±0.3±6.8 and 154.3±1.5±14.3  μb for 7 and 13 TeV. The ratio is 2.14±0.02±0.13, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross sections is larger at lower η than the model prediction.

Abstract:

The decays B+→J/ψ3π+2π− and B+→ψ(2S)π+π+π− are observed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb^-1, collected by the LHCb experiment in proton-proton collisions at the centre-of-mass energies of 7 and 8TeV. The branching fractions relative to that of B+→ψ(2S)K+ are measured to be B(B+ → J/ ψ3π+2π−)/B(B+ → ψ (2S)K+) = (1.88±0.17±0.09)×10^−2, B(B+ → ψ (2S)π+π+π−)/B(B+ → ψ (2S)K+) = (3.04±0.50±0.26)×10^−2,where the first uncertainties are statistical and the second are systematic.

Abstract:

A search for the decays Bc+→J/ψD(∗)0K+ and Bc+→J/ψD(∗)+K∗0 is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb-1. The decays Bc+→J/ψD0K+ and Bc+→J/ψD∗0K+ are observed for the first time, while first evidence is reported for the Bc+→J/ψD∗+K∗0 and Bc+→J/ψD+K∗0 decays. The branching fractions of these decays are determined relative to the Bc+→J/ψπ+ decay. The Bc+ mass is measured, using the J/ψD0K+ final state, to be 6274.28±1.40(stat)±0.32(syst) MeV/c2. This is the most precise single measurement of the Bc+ mass to date.

Abstract:

A search for the B0→K+K− decay is performed using pp-collision data collected by LHCb. The data set corresponds to integrated luminosities of 1.0 and 2.0  fb^−1 at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the B0s→π+π− decay. The measured branching fractions are B(B0→K+K-)=(7.80±1.27±0.81±0.21)×108 and B(B0sπ+π−)=(6.91±0.54±0.63±0.19±0.40)×10^−7. The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the B0→K+π− branching fraction used as a normalization. For the B0s mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into B0s and B0 mesons.