Abstract:

The TORCH time-of-flight (TOF) detector is being developed to provide particle identification up to a momentum of 10 GeV/c over a flight distance of 10 m. It has a DIRC-like construction with thick synthetic amorphous fused-silica plates as a Cherenkov radiator. Photons propagate by total internal reflection to the plate periphery where they are focused onto an array of customised position-sensitive micro-channel plate (MCP) detectors. The goal is to achieve a 15 ps time-of-flight resolution per incident particle by combining arrival times from multiple photons. The MCPs have pixels of effective size 0.4 mm×6.6 mm2 in the vertical and horizontal directions, respectively, by incorporating a novel charge-sharing technique to improve the spatial resolution to better than the pitch of the readout anodes. Prototype photon detectors and readout electronics have been tested and calibrated in the laboratory. Preliminary results from testbeam measurements of a prototype TORCH detector are also presented.

Abstract:

A study of the decay $D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$ is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb$^{-1}$. Decay candidates with muon pairs that have an invariant mass in the range 675--875 MeV$/c^2$ are considered. This region is dominated by the $\rho^{0}$ and $\omega$ resonances. The branching fraction in this range is measured to be ${\cal B}$($D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$ ) = $( 4.17 \pm 0.12(stat) \pm 0.40(syst) )\times10^{-6}$. This is the first observation of the decay $D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$. Its branching fraction is consistent with the value expected in the Standard Model.

Abstract:

Charm meson oscillations are observed in a time-dependent analysis of the ratio of D⁰ → K⁺π⁻π⁺π⁻ to D⁰ → K⁻π⁺π⁻π⁺ decay rates, using data corresponding to an integrated luminosity of 3.0  fb^⁻1 recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes rDK3π and the product of the coherence factor RDK3π and a charm mixing parameter y'K3π. The constraints measured are rDK3π=(5.67±0.12)×10^-2, which is the most precise determination to date, and RDK3π . y'K3π=(0.3 ± 1.8) × 10^-3, which provides useful input for determinations of the CP-violating phase γ in B^± → DK^±, D → K∓π^±π^∓π^± decays. The analysis also gives the most precise measurement of the D⁰ → K⁺π⁻π⁺π⁻ branching fraction, and the first observation of D0 - D0 oscillations in this decay mode, with a significance of 8.2 standard deviations.

Abstract:

Measurements of CP observables in B± → DK± and B± → Dπ± decays are presented where the D meson is reconstructed in the final states K±π∓, π±K∓, K+K−, π+π−, K±π∓π+π−, π±K∓π+π− and π+π−π+π−. This analysis uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb^−1. Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle γ. The analysis of the four-pion D decay mode is the first of its kind.

Abstract:

A search for the decays of the B+c meson to ppπ+ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb-1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, fc/fu × B(B+c → ppπ+) < 3.6×10^-8 in the kinematic region m(pp) < 2.85 GeV/c^2, pT(B) < 20 GeV/c and 2.0 < y(B) < 4.5, where B is the branching fraction and fc(fu) is the fragmentation fraction of the b quark into a Bc+ (B+) meson.