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 CP violation in B 0 → D ∓π± decays

Abstract: A measurement of the CP asymmetries Sf and Sf¯ in B0 → D∓π ± decays is reported. The decays are reconstructed in a dataset collected with the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of 3.0 fb−1 . The CP asymmetries are measured to be Sf = 0.058 ± 0.020(stat) ± 0.011(syst) and Sf¯ = 0.038 ± 0.020(stat) ± 0.007(syst). These results are in agreement with, and more precise than, previous determinations. They are used to constrain angles of the unitarity triangle, |sin (2β + γ)| and γ, to intervals that are consistent with the current world-average valu

Measurement of CP asymmetry in Bs 0 → Ds ∓ K ± decays

Abstract: We report the measurements of the CP-violating parameters in B0 s → D∓ s K± decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb−1 recorded with the LHCb detector. We measure Cf = 0.73 ± 0.14 ± 0.05, A∆Γ f = 0.39 ± 0.28 ± 0.15, A∆Γ f¯ = 0.31 ± 0.28 ± 0.15, Sf = −0.52 ± 0.20 ± 0.07, Sf¯ = −0.49 ± 0.20 ± 0.07, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the B0 s mixing phase, −2βs, to obtain a measurement of the CKM angle γ from B0 s → D∓ s K± decays, yielding γ = (128 +17 −22) ◦ modulo 180◦ , where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8 σ evidence for CP violation in the interference between decay and decay after mixin

Measurements of the branching fractions of Λ c + → pπ − π +, Λ c + → pK−K+, and Λ c + → pπ −K+

Abstract: The ratios of the branching fractions of the decays Λ + c → pπ−π +, Λ + c → pK−K+, and Λ + c → pπ−K+ with respect to the Cabibbo-favoured Λ + c → pK−π + decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb−1 : B(Λ + c → pπ−π +) B(Λ + c → pK−π+) = (7.44 ± 0.08 ± 0.18)%, B(Λ + c → pK−K+) B(Λ + c → pK−π+) = (1.70 ± 0.03 ± 0.03)%, B(Λ + c → pπ−K+) B(Λ + c → pK−π+) = (0.165 ± 0.015 ± 0.005)%, where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the worldaverage value for B(Λ + c → pK−π +), the corresponding branching fractions are B(Λ + c → pπ−π +) = (4.72 ± 0.05 ± 0.11 ± 0.25) × 10−3 , B(Λ + c → pK−K+) = (1.08 ± 0.02 ± 0.02 ± 0.06) × 10−3 , B(Λ + c → pπ−K+) = (1.04 ± 0.09 ± 0.03 ± 0.05) × 10−4

Highlights from the LHCb experiment

We report recent results by the LHCb collaboration in heavy-ion collisions in collider and fixed-target mode at the LHC. A large variety of measurements show the potential of LHCb in nuclear collisions

Measurement of branching fractions of charmless four-body Λb 0 and Ξb 0 decays

A search for charmless four-body decays of Λ 0 b and Ξ0 b baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb−1 . Six decay modes are observed, among which Λ 0 b → pK−π +π −, Λ 0 b → pK−K+K−, Ξ0 b → pK−π +π − and Ξ0 b → pK−π +K− are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the Ξ0 b baryon) are determined relative to the Λ 0 b → Λ + c π − decay

First observation of B + → Ds + K + K − decays and a search for B + → Ds + ϕ decays

A search for B+ → D+ s K+K− decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb−1 , collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be B(B + → D+ s K+K−) = (7.1 ± 0.5 ± 0.6 ± 0.7) × 10−6 , where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+ → D+ sD 0 . A search is also performed for the pure annihilation decay B+ → D+ s φ. No significant signal is observed and a limit of B(B + → D+ s φ) < 4.9 × 10−7 (4.2 × 10−7 ) is set on the branching fraction at 95% (90%) confidence level. Keywords: B physics, Branching fraction, Hadron-Hadron scattering (experiments), Rare deca

Search for the Lepton-Flavor-Violating Decays Bs0 →τ±μâ' and B0 →τ±μâ'

Results are reported from a search for the rare decays Bs0→τ±μâ' and B0→τ±μâ', where the τ lepton is reconstructed in the channel τ-→π-π+π-ντ. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb-1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μâ', the upper limit B(Bs0→τ±μâ')<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μâ' is assumed, a limit of B(B0→τ±μâ')<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μâ') and the most stringent limit on B(B0→τ±μâ')

Measurement of Ds ± production asymmetry in pp collisions at √s=7 and 8 TeV

Abstract: The inclusive D± s production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of √ s = 7 and 8 TeV. Promptly produced D± s mesons are used, which decay as D± s → φπ±, with φ → K+K−. The measurement is performed in bins of transverse momentum, pT, and rapidity, y, covering the range 2.5 < pT < 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero D± s production asymmetry is found with a significance of 3.3 standard deviations

Studies of the resonance structure in D0→ K∓π±π±π∓ decays

Amplitude models are constructed to describe the resonance structure of D0 → K −π+π+π− and D0 → K +π−π−π+ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 f b−1. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes D0 → a1(1260)+K − and D0 → K1(1270/1400)+π− being prominent in D0 → K −π+π+π− and D0 → K +π−π−π+, respectively. Precise measurements of the lineshape parameters and couplings of the a1(1260)+, K1(1270)− and K(1460)− resonances are made, and a quasi model-independent study of the K(1460)− resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be RK3π = 0.459 ± 0.010 (stat) ± 0.012 (syst)±0.020 (model), which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle γ and studies of charm mixing and CP violation