Malcolm John

Abstract:

We present a measurement of the time-dependent CP-violating asymmetry in Bs0→J/ψ decays, using data collected with the LHCb detector at the LHC. The decay time distribution of Bs0→J/ψ is characterized by the decay widths Γ H and Γ L of the heavy and light mass eigenstates, respectively, of the Bs0-B̄s0 system and by a CP-violating phase s. In a sample of about 8500 Bs0→J/ψevents isolated from 0.37fb -1 of pp collisions at √s=7TeV, we measure s=0.15±0.18(stat)±0.06(syst)rad. We also find an average Bs0 decay width Γ s (Γ L+Γ H)/2=0.657±0.009(stat)±0.008(syst)ps -1 and a decay width difference ΔΓ s Γ L- Γ H=0.123±0.029(stat)±0.011(syst)ps -1. Our measurement is insensitive to the transformation ( s, ΔΓ s) (π- s,-ΔΓ s). © 2012 CERN. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract:

A search is performed for the lepton number violating decay B +→h -μ +μ +, where h - represents a K - or a π -, using an integrated luminosity of 36pb -1 of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B +→K -μ +μ +)<5. 4×10 -8 and B(B +→π -μ +μ +)<5.8×10 -8 are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively. © 2012 CERN, for the LHCb Collaboration. Published by the American Physical Society under the terms of the http://creativecommons.org/licenses/by/3.0/. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract:

Measurements of b-hadron masses are performed with the exclusive decay modes B +→J/ψK +, B 0→J/ψK +, B0→J/ψKS0, Bs0→J/ψφ and Λb0→J/ψΛ using an integrated luminosity of 35pb -1 collected in pp collisions at a centre-of-mass energy of 7 TeV by the LHCb experiment. The momentum scale is calibrated with J/ψ→μ +μ - decays and verified to be known to a relative precision of 2 ×10 -4 using other two-body decays. The results are more precise than previous measurements, particularly in the case of the Bs0 and Λb0 masses. © 2012 CERN.

Abstract:

Measurements of b hadron production ratios in proton-proton collisions at a center-of-mass energy of 7 TeV with an integrated luminosity of 3pb -1 are presented. We study the ratios of strange B meson to light B meson production f s/(f u+f d) and Λb0 baryon to light B meson production f Λb/(f u+f d) as a function of the charmed hadron-muon pair transverse momentum p T and the b hadron pseudorapidity η, for p T between 0 and 14 GeV and η between 2 and 5. We find that f s/(f u+f d) is consistent with being independent of p T and η, and we determine f s/(f u+f d)=0.134±0.004-0.010+0.011, where the first error is statistical and the second systematic. The corresponding ratio f Λb/(f u+f d) is found to be dependent upon the transverse momentum of the charmed hadron-muon pair, f Λb/(f u+f d)=(0.404±0. 017(stat)±0.027(syst)±0.105(Br))×[1-(0.031±0. 004(stat)±0.003(syst))×p T(GeV)], where Br reflects an absolute scale uncertainty due to the poorly known branching fraction B(Λc+→pK -π +). We extract the ratio of strange B meson to light neutral B meson production f s/f d by averaging the result reported here with two previous measurements derived from the relative abundances of B̄s0→Ds+π - to B ̄0→D +K - and B ̄0→ D +π -. We obtain f s/f d=0.267-0. 020+0.021. © 2012 CERN.

Abstract:

A search for the decays Bs0→μ+μ- and B 0→μ +μ - is performed with 0.37 fb -1 of pp collisions at s=7 TeV collected by the LHCb experiment in 2011. The upper limits on the branching fractions are B(Bs0→μ+μ-)<1.6×10-8 and B(B0→μ+μ-)<3.6×10-9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to B(Bs0→μ+μ-)<1.4×10-8 and B(B0→μ+μ-)<3.2×10-9 at 95% confidence level. © 2012 CERN.