Measurement of the effective B0s→K+K− lifetime

A precise determination of the effective B0 s → K + K − lifetime can be used to constrain contributions from physics beyond the Standard Model in the B0 s meson system. Conventional approaches select B meson decay products that are significantly displaced from the B meson production vertex. As a consequence, B mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0 fb−1 of data recorded by the LHCb experiment, the effective B0 s → K + K − lifetime is measured as 1.455 ± 0.046 (stat.) ± 0.006 (syst.) ps. © 2012 CERN. Published by Elsevier B.V. All rights reserved

First observation of Bs→Ds2∗+Xμν decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B0 s → D+ s Xμ−ν and B0 s → D0 K + Xμ−ν are detected. Two struc- tures are observed in the D0 K + mass spectrum at masses consistent with the known D s1(2536)+ and D∗ s2(2573)+ mesons. The measured branching fractions relative to the total B0 s semileptonic rate are B(B0 s → D∗+ s2 Xμ−ν)/B(B0 s → Xμ−ν) = (3.3 ± 1.0 ± 0.4)%, and B(B0 s → D+ s1 Xμ−ν)/B(B0 s → Xμ−ν) = (5.4 ± 1.2 ± 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D∗+ s2 state in B0 s decays; we also measure its mass and widt

Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of B0s meson decays to J/ψη and J/ψη′

First evidence of the B0 → J/ψω decay is found and the B0 s → J/ψη and B0 s → J/ψη decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in proton–proton collisions at a centre-of-mass energy of √s = 7 TeV.

Study of η − η′ mixing from measurement of B (s)0 → J/ψη(′) decay rates

A study of B and B0 s meson decays into J/ψη and J/ψη0 final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψη0 is observed for the first time. The following ratios of branching fractions are measured: B(B0 → J/ψη0 ) B(B0 s → J/ψη0) = (2.28 ± 0.65 (stat) ± 0.10 (syst) ± 0.13 (fs/fd)) × 10−2 , B(B0 → J/ψη) B(B0 s → J/ψη) = (1.85 ± 0.61 (stat) ± 0.09 (syst) ± 0.11 (fs/fd)) × 10−2 , where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a B0 s or a B0 meson. The branching fraction ratios are used to determine the parameters of η−η 0 meson mixing. In addition, the first evidence for the decay B0 s → ψ(2S)η 0 is reported, and the relative branching fraction is measured, B(B0 s → ψ(2S)η 0 ) B(B0 s → J/ψη0) = (38.7 ± 9.0 (stat) ± 1.3 (syst) ± 0.9(B)) × 10−2 , where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons

Model-independent evidence for J /ψp contributions to Λb0 →j /ψpK- decays

The data sample of Λ0b→J/ψpK− decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3  fb−1, is inspected for the presence of J/ψp or J/ψK− contributions with minimal assumptions about K−p contributions. It is demonstrated at more than nine standard deviations that Λ0b→J/ψpK− decays cannot be described with K−p contributions alone, and that J/ψp contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P+c→J/ψp charmonium-pentaquark states in the same data sample

Measurement of the CP asymmetry in B − → Ds − D 0 and B − → D − D 0 decays

Abstract: The CP asymmetry in B− → D− s D0 and B− → D−D0 decays is measured using LHCb data corresponding to an integrated luminosity of 3.0 fb−1 , collected in pp collisions at centre-of-mass energies of 7 and 8 TeV. The results are ACP (B− → D− s D0 ) = (−0.4 ± 0.5 ± 0.5)% and ACP (B− → D−D0 ) = (2.3 ± 2.7 ± 0.4)%, where the first uncertainties are statistical and the second systematic. This is the first measurement of ACP (B− → D− s D0 ) and the most precise determination of ACP (B− → D−D0 ). Neither result shows evidence of CP violation

Measurement of the track reconstruction efficiency at LHCb

The determination of track reconstruction efficiencies at LHCb using J/ψ → µ +µ − decays is presented. Efficiencies above 95% are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of 0.8% for data taking in 2010, and at a precision of 0.4% for data taking in 2011 and 2012. For hadrons an additional 1.4% uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb

Observation of the B0 →ρ0ρ0 decay from an amplitude analysis of B0 → (π+π-) (π+π-) decays

Proton-proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb−1 , are analysed to search for the charmless B0 → ρ 0ρ 0 decay. More than 600 B0 → (π +π −)(π +π −) signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0 → ρ 0ρ 0 decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0 → ρ 0ρ 0 decays yielding a longitudinally polarised final state is measured to be fL = 0.745+0.048 −0.058(stat) ± 0.034(syst). The B0 → ρ 0ρ 0 branching fraction, using the B0 → φK∗ (892)0 decay as reference, is also reported as B(B0 → ρ 0ρ 0 ) = (0.94 ± 0.17(stat) ± 0.09(syst) ± 0.06(BF)) × 10−6