Strong constraints on the b → sγ photon polarisation from B 0 → K *0 e + e − decays

An angular analysis of the B0 → K∗0 e +e − decay is performed using a data sample corresponding to an integrated luminosity of 9 fb−1 of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (q 2 ) interval between 0.0008 and 0.257 GeV2 , where the rate is dominated by the B0 → K∗0γ transition with a virtual photon. The fraction of longitudinal polarisation of the K∗0 meson, FL, is measured to be FL = (4.4 ± 2.6 ± 1.4)%, where the first uncertainty is statistical and the second systematic. The ARe T observable, which is related to the lepton forward-backward asymmetry, is measured to be ARe T = −0.06 ± 0.08 ± 0.02. The A (2) T and AIm T transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be A (2) T = 0.11 ± 0.10 ± 0.02 and AIm T = 0.02 ± 0.10 ± 0.01. The results are consistent with Standard Model predictions and provide the world's best constraint on the b → sγ photon polarisation

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

A measurement of the CP asymmetry difference between Λc + → pK − K + and pπ−π+ decays

The difference between the CP asymmetries in the decays Λ + c → pK−K+ and Λ + c → pπ−π + is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb−1 . The Λ + c candidates are reconstructed as part of the Λ 0 b → Λ + c µ −X decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Λ + c → pπ−π + sample. This alters the definition of the integrated CP asymmetry to A wgt CP (pπ−π +). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Λ + c decay phase space. The difference in CP asymmetries is found to be ∆A wgt CP = ACP (pK−K+) − A wgt CP (pπ−π +) = (0.30 ± 0.91 ± 0.61) %, where the first uncertainty is statistical and the second is systemati

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

Measurement of the CKM angle γ using B ± → DK ± with D → K S 0 π + π −, K S 0 K + K − decays

Abstract: A binned Dalitz plot analysis of B± → DK± decays, with D → K0 S π +π − and D → K0 SK+K−, is used to perform a measurement of the CP-violating observables x± and y±, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ. The analysis is performed without assuming any D decay model, through the use of information on the strong-phase variation over the Dalitz plot from the CLEO collaboration. Using a sample of proton-proton collision data collected with the LHCb experiment in 2015 and 2016, and corresponding to an integrated luminosity of 2.0 fb−1 , the values of the CP violation parameters are found to be x− = (9.0±1.7±0.7±0.4)×10−2 , y− = (2.1±2.2±0.5±1.1)× 10−2 , x+ = (−7.7±1.9±0.7±0.4)×10−2 , and y+ = (−1.0±1.9±0.4±0.9)×10−2 . The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the strong-phase measurements. These values are used to obtain γ = 87 +11 −12 ◦ , rB = 0.086+0.013 −0.014, and δB = (101±11)◦ , where rB is the ratio between the suppressed and favoured B-decay amplitudes and δB is the corresponding strong-interaction phase difference. This measurement is combined with the result obtained using 2011 and 2012 data collected with the LHCb experiment, to give γ = 80 +10 −9 ◦ , rB = 0.080 ± 0.011, and δB = (110 ± 10)

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 forward top pair production in the dilepton channel in pp collisions at √s=13 TeV

Forward top quark pair production is studied in pp collisions in the µeb final state using a data sample corresponding to an integrated luminosity of 1.93 fb−1 collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted ∆R, between the two leptons must be larger than 0.1. The b-jet axis is required to be separated from both leptons by a ∆R of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be σtt¯ = 126 ± 19 (stat) ± 16 (syst) ± 5 (lumi) fb where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction

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

First measurement of the CP-violating phase ϕsdd¯ in Bs 0 → (K + π −)(K − π +) decays

A flavour-tagged decay-time-dependent amplitude analysis of B0 s → (K+π −)(K−π +) decays is presented in the K±π ∓ mass range from 750 to 1600 MeV/c 2 . The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb−1 . Several quasi-two-body decay modes are considered, corresponding to K±π ∓ combinations with spin 0, 1 and 2, which are dominated by the K∗ 0 (800)0 and K∗ 0 (1430)0 , the K∗ (892)0 and the K∗ 2 (1430)0 resonances, respectively. The longitudinal polarisation fraction for the B0 s → K∗ (892)0K ∗ (892)0 decay is measured as fL = 0.208 ± 0.032 ± 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CP-violating phase, φ dd¯ s , in b → d ¯ds transitions is performed, yielding a value of φ dd¯ s = −0.10 ± 0.13 (stat) ± 0.14 (syst) rad