LHCb

Abstract:

© 2014, Springer Verlag. All rights reserved. A search for CP violation in Cabibbo-suppressed D± → K0 SK± and D± s → K0 Sπ± decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb-1, recorded by the LHCb experiment. The individual CP-violating asymmetries are measured to be (Formula presented.) assuming that CP violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmetries for the four decay modes D± (s) → K0 SK± and D± (s) → K0 Sπ± gives the sum (Formula presented.). In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation.

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.