Sneha Malde

Abstract:

The calibration and performance of the opposite-side flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been developed using simulated events and optimized and calibrated with B⁺→J/ψK⁺, B⁰→J/ψK^*0 and B⁰→D^*-μ⁺νμ decay modes with 0. 37 fb^-1 of data collected in pp collisions at s = 7 TeV during the 2011 physics run. The opposite-side tagging power is determined in the B⁺→J/ψK⁺ channel to be (2. 10±0. 08±0. 24) %, where the first uncertainty is statistical and the second is systematic. © 2012 CERN for the benefit of the LHCb collaboration.

Abstract:

The first measurements of the coherence factor RKS0Kπ and the average strong-phase difference δDKS0Kπ in D0→KS0K ∓π± decays are reported. These parameters can be used to improve the determination of the unitary triangle angle γ in B-→D∼K- decays, where D∼ is either a D0 or a D̄0 meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully reconstructed D0D̄0 pairs produced in e+e- collisions at the ψ(3770) resonance. The measured values are RKS0Kπ=0. 73±0.08 and δDKS0Kπ=(8.3±15.2)° for an unrestricted kinematic region and RK*K=1.00±0.16 and δDK *K=(26.5±15.8)° for a region where the combined KS0π± invariant mass is within 100MeV/c2 of the K *(892)± mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K *(892)± resonance. The branching ratio B(D0→KS0K+π-)/B(D0→KS0K -π+) is determined to be 0.592±0.044(stat) ±0.018(syst), which is more precise than previous measurements. © 2012 American Physical Society.

Abstract:

First observations of the Cabibbo-suppressed decays B¯0 → D+K-π+π- and B- → D0K-π+π- are reported using 35 pB-1 of data collected with the LHCb detector. Their branching fractions are measured with respect to the corresponding Cabibbo-favored decays, from which we obtain B(B¯0→ D+K-π+π-)/B(B¯0→D+π-π+π-)=(5.9±1.1±0.5)×10-2 and B(B-→D0K-π+π-)/B(B-→ D0π-π+π-)=(9.4±1.3±0.9)×10-2, where the uncertainties are statistical and systematic, respectively. The B- → D0K-π+π- decay is particularly interesting, as it can be used in a similar way to B- → D0K- to measure the Cabibbo-Kobayashi-Maskawa phase γ. © 2012 CERN.

Abstract:

The decay B̄s0→J/ψK +K - is investigated using 0.16fb -1 of data collected with the LHCb detector using 7 TeV pp collisions. Although the J/ψ channel is well known, final states at higher K +K - masses have not previously been studied. In the K +K - mass spectrum we observe a significant signal in the f2′(1525) region as well as a nonresonant component. After subtracting the nonresonant component, we find B(B̄s0→J/ψf2′(1525))/ B(B̄s0→J/ψ)=(26.4±2.7±2.4)%. © 2012 CERN.

Abstract:

Charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of √S = 7 TeV in different intervals of pseudorapidity η. Charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the η ranges -2.5<η<-2.0 and 2.0<η<4.5. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of η. In general, the models underestimate charged particle production. © 2012 CERN for the benefit of the LHCb collaboration.