Malcolm John

Abstract:

Low mass on-detector cooling systems are being developed and studied by the Detector Technology group (PH-DT) in the CERN Physics Department in close collaboration with LHC and non-LHC experiments. Two approaches are currently being investigated. The first approach, for barrel configurations, consists in integrating the cooling apparatus in light mechanical structures supporting the detectors. In this case, the thermal management can be achieved either with light cooling pipes and thin plates or with a network of microchannels embedded in thin strips of silicon or polyimide. Both configurations are being investigated in the context of the 2018 upgrade program of the ALICE Inner Tracking System (ITS). Moreover, it is also possible to use a silicon microchannel cooling device itself as structural support for the detectors and electronics. Such a configuration has been adopted by the NA62 collaboration for their GigaTracKer (GTK) as well as by the LHCb collaboration for the 2018 major upgrade of the Vertex Locator (VeLo).

Abstract:

The branching fraction of the rare decay B 0 → K *0 e + e - in the dilepton mass region from 30 to 1000 MeV/c 2 has been measured by the LHCb experiment, using pp collision data, corresponding to an integrated luminosity of 1.0 fb-1, at a centre-of-mass energy of 7 TeV. The decay mode B 0 → J/ψ (e + e -)K *0 is utilized as a normalization channel. The branching fraction B(B 0 → K *0 e + e -) is measured to be B(B 0 → K *0 e + e -)30-1000 MeV/c2=(3.1+0.9-0.80.2-0.3 ± 0.2) × 10 -7 where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B 0 → J/ψ K *0 and J/ψ → e + e - branching fractions. [Figure not available: see fulltext.] © 2013 Cern for the benefit of the LHCb collaboration.

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.