Abstract:

The TORCH detector is being developed for low-momentum particle identification, combining time-of-flight and Cherenkov techniques to achieve charged particle pi/K/p separation up to 10 GeV/c over a flight distance of 10m. This requires a timing resolution of 70 ps for single photons. Based on an existing scalable design, production and testing of a TORCH readout system has been undertaken over the past year, and a novel customized Micro Channel Plate (MCP) photomultiplier device with 128-channels has been instrumented. This paper will report on the development of the readout system which is being used to measure time-of-flight in a test-beam, and its performance. We will also discuss the communication and data alignment between the TORCH system and the TimePix3 telescope in order to provide track reconstruction.

Abstract:

The first model-independent measurement of the charm mixing parameters in the decay $D^0 \to K_S \pi^+ \pi^-$ is reported, using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ at a centre-of-mass energy of 7 TeV. The measured values are \begin{eqnarray*} x and=and (-0.86 \pm 0.53 \pm 0.17) \times 10^{-2}, \\ y and=and (+0.03 \pm 0.46 \pm 0.13) \times 10^{-2}, \end{eqnarray*} where the first uncertainties are statistical and include small contributions due to the external input for the strong phase measured by the CLEO collaboration, and the second uncertainties are systematic.

Abstract:

Amplitude models are applied to studies of resonance structure in D0→KS0K-π+ and D0→KS0K+π- decays using pp collision data corresponding to an integrated luminosity of 3.0 fb-1 collected by the LHCb experiment. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of 100 MeV/c2 around the K∗(892)± resonance. Two formulations for the Kπ S-wave are used, both of which give a good description of the data. The ratio of branching fractions B(D0→KS0K+π-)/B(D0→KS0K-π+) is measured to be 0.655±0.004(stat)±0.006(syst) over the full phase space and 0.370±0.003(stat)±0.012(syst) in the restricted region. A search for CP violation is performed using the amplitude models and no significant effect is found. Predictions from SU(3) flavor symmetry for K∗(892)K amplitudes of different charges are compared with the amplitude model results.

Abstract:

Production cross-sections of prompt charm mesons are measured with the first data from pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 4.98 ± 0.19 pb⁻¹ collected by the LHCb experiment. The production cross-sections of D⁰, D⁺, D_s⁺, and D^*+ mesons are measured in bins of charm meson transverse momentum, p_T, and rapidity, y, and cover the range 0 < p_T < 15GeV/c and 2.0 < y < 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 < p_T < 8 GeV/c are found to be
σ(pp →D⁰X) = 2460 ± 3 ± 130 μb
σ(pp →D⁺X) = 1000 ± 3 ± 110 μb
σ(pp →D⁺_sX) = 460 ± 13 ± 100 μb
σ(pp →D^∗+X)=880 ± 5 ± 140 μb
where the uncertainties are due to statistical and systematic uncertainties, respectively.

Abstract:

Study of ψ(2S) production and cold nuclear matter effects in pPb collisions at √s_NN = 5 TeV

The production of ψ(2S) mesons is studied in dimuon final states using proton-lead (pPb) collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of 1.6 nb⁻¹. The nucleon-nucleon centre-of-mass energy of the pPb collisions is √s_NN = 5 TeV. The measurement is performed using ψ(2S) mesons with transverse momentum less than 14 GeV/c and rapidity y in the ranges 1.5 < y < 4.0 and −5.0 < y < −2.5 in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modification factor are determined for ψ(2S) mesons. Using the production cross- section results of ψ(2S) and J/ψ mesons from b-hadron decays, the bb̅ cross-section in pPb collisions at √s_NN = 5 TeV is obtained.