Guy Wilkinson

Abstract:

The $B^{\pm}$ meson production asymmetry in $pp$ collisions is measured using $B^+ \to \bar{D}^0 \pi^+$ decays. The data were recorded by the LHCb experiment during Run 1 of the LHC at centre-of-mass energies of $\sqrt{s}=$ 7 and 8 TeV. The production asymmetries, integrated over transverse momenta in the range $2 < p_{\rm T} < 30$ GeV/$c$, and rapidities in the range $2.1 < y < 4.5$, are measured to be \begin{align*} \mathcal{A}_{\rm prod}(B^+,\sqrt{s}=7~{\rm TeV}) &= (-0.41 \pm 0.49 \pm 0.10) \times 10^{-2},\\ \mathcal{A}_{\rm prod}(B^+,\sqrt{s}=8~{\rm TeV}) &= (-0.53 \pm 0.31 \pm 0.10) \times 10^{-2}, \end{align*} where the first uncertainties are statistical and the second are systematic. These production asymmetries are used to correct the raw asymmetries of $B^{+} \to J/\psi K^{+}$ decays, thus allowing a measurement of the $CP$ asymmetry, \begin{equation*} \mathcal{A}_{CP} = (0.09 \pm 0.27 \pm 0.07) \times 10^{-2}. \end{equation*}

Abstract:

A measurement of the phase difference between the short- and long-distance contributions to the B+→K+μ+μ− decay is performed by analysing the dimuon mass distribution. The analysis is based on pp collision data corresponding to an integrated luminosity of 3fb^-1 collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the B+→K+μ+μ− decay is modelled as a sum of relativistic Breit-Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the J/ψ and ψ(2S) resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, C9 and C10, and the branching fraction of the short-distance component is measured.

Abstract:

The ratio of branching fractions and the difference in CP asymmetries of the decays B+ → J/ψπ+ and B+ → J/ψK+ are measured using a data sample of pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 3 fb^−1 at centre-of-mass energies of 7 and 8 TeV. The results are B(B+→J/ψπ+)/B(B+→J/ψK+)=(3.83±0.03±0.03)×10^−2, ACP(B+→J/ψπ+)−ACP(B+→J/ψK+)=(1.82±0.86±0.14)×10^−2, where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of A^CP (B+ → J/ψK+) provides the most precise estimate to date of CP violation in the decay B+→J/ψπ+, A^CP(B+→J/ψπ+)=(1.91±0.89±0.16)×10^−2..