Malcolm John

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.

Abstract:

Measurement of mixing-induced CP violation in B-s0 decays is of prime importance in probing new physics. So far only the channel B- s 0→J/ψφ has been used. Here we report on a measurement using an LHCb data sample of 0.41 fb -1, in the CP odd eigenstate J/ψf 0(980), where f 0(980)→π +π -. A time-dependent fit of the data with the B-s0 lifetime and the difference in widths of the heavy and light eigenstates constrained to the values obtained from B-s0→J/ψφ yields a value of the CP violating phase of -0.44±0.44±0.02 rad, consistent with the Standard Model expectation. © 2012 CERN.