LHCb

Abstract:

A search for previously unobserved decays of beauty baryons to the final states K0 spπ- and K0 spK- is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb- of pp collisions. The Λ0 b → ̄K pπ- decay is observed with a significance of 8.6σ, with branching fraction (Equation Presented), where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions f Λ 0 b/fd, and from the branching fraction of the B0 → K0π+π - normalisation channel, respectively. A first measurement is made of the CP asymmetry, giving (Equation Presented). No significant signals are seen for Λ0 b → K0 spK - decays, Ξ0 b decays to both the K 0 spπ- and K0 spK - final states, and the Λ0 b → D- s(→ K0 sK-)p decay, and upper limits on their branching fractions are reported.

Abstract:

©Open Access. The production of J/ψ mesons with rapidity 1.5 < y < 4.0 or −5.0 < y < −2.5 and transverse momentum pT < 14 GeV/c is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy √SNN = 5 TeV. The J/ψ mesons are reconstructed using the dimuon decay mode. The analysis is based on a data sample corresponding to an integrated luminosity of about 1.6 nb−1. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt J/ψ mesons and J/ψ from b-hadron decays. Clear suppression of prompt J/ψ production with respect to proton-proton collisions at large rapidity is observed, while the production of J/ψ from b-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.

Abstract:

TORCH is an innovative high-precision time-of-flight system to provide particle identification in the difficult intermediate momentum region up to 10 GeV/c. It is also suitable for large-area applications. The detector provides a time-of-flight measurement from the imaging of Cherenkov photons emitted in a 1 cm thick quartz radiator. The photons propagate by total internal reflection to the edge of the quartz plate, where they are focused onto an array of photon detectors at the periphery. A time-of-flight resolution of about 10-15 ps per incident charged particle needs to be achieved for a three sigma kaon-pion separation up to 10 GeV/c momentum for the TORCH located 9.5 m from the interaction point. Given ∼ 30 detected photons per incident charged particle, this requires measuring the time-ofarrival of individual photons to about 70 ps. This paper will describe the design of a TORCH prototype involving a number of ground-breaking and challenging techniques.

Abstract:

The LHCb RICH1 detector uses hybrid photon detectors (HPDs) as its optical sensors. A calibration system has been constructed to provide corrections for distortions that are primarily due to external magnetic fields. We describe here the system design, construction, operation and performance. © 2013 Elsevier B.V.