LHCb

Abstract:

A combination of three LHCb measurements of the CKM angle γ is presented. The decays B±→DK± and B±→Dπ± are used, where D denotes an admixture of D0 and D-0 mesons, decaying into K+K-, π+π-, K±π∓, K±π∓π±π∓, KS0π+π-, or KS0K+K- final states. All measurements use a dataset corresponding to 1.0 fb-1 of integrated luminosity. Combining results from B±→DK± decays alone a best-fit value of γ=72.0° is found, and confidence intervals are setγ∈[56.4,86.7]°at 68% CL,γ∈[42.6,99.6]°at 95% CL. The best-fit value of γ found from a combination of results from B±→Dπ± decays alone, is γ=18.9°, and the confidence intervalsγ∈[7.4,99.2]°∪[167.9,176.4]°at 68% CL are set, without constraint at 95% CL. The combination of results from B±→DK± and B±→Dπ± decays gives a best-fit value of γ=72.6° and the confidence intervalsγ∈[55.4,82.3]°at 68% CL,γ∈[40.2,92.7]°at 95% CL are set. All values are expressed modulo 180°, and are obtained taking into account the effect of D0-D-0 mixing. © 2013 CERN.

Abstract:

Local thermal management of detector electronics through ultra-thin micro-structured silicon cooling plates is a very promising technique for pixel detectors in high energy physics experiments, especially at the LHC where the heavily irradiated sensors must be operated at temperatures below -20 C. It combines a very high thermal efficiency with a very low addition of mass and space, and suppresses all problems of CTE mismatch between the heat source and the heat sink. In addition, the use of CO2 as evaporative coolant liquid brings all the benefits of reliable and stable operation, but the high pressures involved impose additional challenges on the micro channel design and the fluidic connectivity. A series of designs have already been prototyped and tested for LHCb. The challenges, the current status of the measurements and the solutions under development will be described. © 2013 Elsevier B.V.

Abstract:

A search for CP violation in the phase-space structures of D0 and D-0 decays to the final states K-K+π-π+ and π-π+π+π- is presented. The search is carried out with a data set corresponding to an integrated luminosity of 1.0 fb-1 collected in 2011 by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. For the K-K+π-π+ final state, the four-body phase space is divided into 32 bins, each bin with approximately 1800 decays. The p-value under the hypothesis of no CP violation is 9.1%, and in no bin is a CP asymmetry greater than 6.5% observed. The phase space of the π-π+π+π- final state is partitioned into 128 bins, each bin with approximately 2500 decays. The p-value under the hypothesis of no CP violation is 41%, and in no bin is a CP asymmetry greater than 5.5% observed. All results are consistent with the hypothesis of no CP violation at the current sensitivity. © 2013 CERN.

Abstract:

The first observation of the decay B0s → χc1φ and a study of B0 → χc1,2K*0 decays are presented. The analysis is performed using a dataset, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. The following ratios of branching fractions are measured: Where the third uncertainty is due to the limited knowledge of the branching fractions of χc → J/ψγ modes. © 2013 CERN. Published by Elsevier B.V.

Abstract:

The LHCb experiment has been taking data at the Large Hadron Collider (LHC) at CERN since the end of 2009. One of its key detector components is the Ring-Imaging Cherenkov (RICH) system. This provides charged particle identification over a wide momentum range, from 2-100 GeV/c. The operation and control, software, and online monitoring of the RICH system are described. The particle identification performance is presented, as measured using data from the LHC. Excellent separation of hadronic particle types (π, K, p) is achieved. © 2013 CERN for the benefit of the LHCb collaboration.