84 research outputs found

    Search for CP violation in Λb0→pK− and Λb0→pπ− decays

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    A search for CP violation in Λb0→pK− and Λb0→pπ− decays is presented using a sample of pp collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0fb−1. The CP -violating asymmetries are measured to be ACPpK−=−0.020±0.013±0.019 and ACPpπ−=−0.035±0.017±0.020, and their difference ACPpK−−ACPpπ−=0.014±0.022±0.010, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date

    Measurement of the CP asymmetry in B- -> (Ds-D0) and B- -> (D-D0) decays

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    The CP asymmetry in B- -> (Ds-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 8TeV. The results are A(CP) (B- -> (Ds-D0)) = (-0.4 +/- 0.5 +/- 0.5)% and A(CP) (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 A(CP) (B- -> (Ds-D0)) and the most precise determination of A(CP) (B- -> (D-D0)). Neither result shows evidence of CP violation

    Measurement of the CKM angle γ\gamma using B0DK0B^0 \rightarrow D K^{*0} with DKS0π+πD \rightarrow K^0_S \pi^+ \pi^- decays

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    A model-dependent amplitude analysis of the decay B0D(KS0π+π)K0B^0\rightarrow D(K^0_S\pi^+\pi^-) K^{*0} is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0fb1^{-1}, recorded at s=7\sqrt{s}=7 and 8TeV8 TeV by the LHCb experiment. The CP violation observables x±x_{\pm} and y±y_{\pm}, sensitive to the CKM angle γ\gamma, are measured to be \begin{eqnarray*} x_- &=& -0.15 \pm 0.14 \pm 0.03 \pm 0.01, y_- &=& 0.25 \pm 0.15 \pm 0.06 \pm 0.01, x_+ &=& 0.05 \pm 0.24 \pm 0.04 \pm 0.01, y_+ &=& -0.65^{+0.24}_{-0.23} \pm 0.08 \pm 0.01, \end{eqnarray*} where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the DKS0π+πD\rightarrow K^0_S \pi^+\pi^- amplitude model. These are the most precise measurements of these observables. They correspond to γ=(8022+21)\gamma=(80^{+21}_{-22})^{\circ} and rB0=0.39±0.13r_{B^0}=0.39\pm0.13, where rB0r_{B^0} is the magnitude of the ratio of the suppressed and favoured B0DK+πB^0\rightarrow D K^+ \pi^- decay amplitudes, in a KπK\pi mass region of ±50MeV\pm50 MeV around the K(892)0K^*(892)^0 mass and for an absolute value of the cosine of the K0K^{*0} decay angle larger than 0.40.4.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-007.htm

    Search for dark photons produced in 13 TeV pppp collisions

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    Searches are performed for both promptlike and long-lived dark photons, A 0 , produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A 0 → μ þ μ − decays and a data sample corresponding to an integrated luminosity of 1 . 6 fb − 1 collected with the LHCb detector. The promptlike A 0 search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A 0 search is restricted to the low-mass region 214 <m ð A 0 Þ < 350 MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the γ – A 0 kinetic-mixing strength. The constraints placed on promptlike dark photons are the most stringent to date for the mass range 10 . 6 <m ð A 0 Þ < 70 GeV, and are comparable to the best existing limits for m ð A 0 Þ < 0 . 5 GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature

    Search for the decay Bs0D0f0(980) {B}_s^0\to {\overline{D}}^0{f}_0(980)

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    A search for Bs0D0f0(980)B_s^0 \to \overline{D}^{0} f_{0}(980) decays is performed using 3.0fb13.0\, {\rm fb}^{-1} of pppp collision data recorded by the LHCb experiment during 2011 and 2012. The f0(980)f_{0}(980) meson is reconstructed through its decay to the π+π\pi^{+}\pi^{-} final state in the mass window 900MeV/c2<m(π+π)<1080MeV/c2900\, {\rm MeV}/c^{2} < m(\pi^{+}\pi^{-}) < 1080\, {\rm MeV}/c^{2}. No significant signal is observed. The first upper limits on the branching fraction of B(Bs0D0f0(980))<3.1(3.4)×106\mathcal{B}(B_s^0 \to \overline{D}^{0} f_{0}(980)) < 3.1\,(3.4) \times 10^{-6} are set at 90%90\,\% (95%95\,\%) confidence level.Comment: 20 pages, 2 figures, published in JHE

    Measurement of CPCP asymmetry in Bs0DsK±B_s^0 \to D_s^{\mp} K^{\pm} decays

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    We report the measurements of the CPCP-violating parameters in Bs0DsK±B_s^0 \to D_s^{\mp} K^{\pm} decays observed in pppp collisions, using a data set corresponding to an integrated luminosity of 3.0fb13.0\,\text{fb}^{-1} recorded with the LHCb detector. We measure Cf=0.73±0.14±0.05C_f = 0.73 \pm 0.14 \pm 0.05, AfΔΓ=0.39±0.28±0.15A^{\Delta \Gamma}_f = 0.39 \pm 0.28 \pm 0.15, AfΔΓ=0.31±0.28±0.15A^{\Delta \Gamma}_{\overline{f}} = 0.31 \pm 0.28 \pm 0.15, Sf=0.52±0.20±0.07S_f = -0.52 \pm 0.20 \pm 0.07, Sf=0.49±0.20±0.07S_{\overline{f}} = -0.49 \pm 0.20 \pm 0.07, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the Bs0B_s^0 mixing phase, 2βs-2\beta_s, to obtain a measurement of the CKM angle γ\gamma from Bs0DsK±B_s^0 \to D_s^{\mp} K^{\pm} decays, yielding \gamma = (128\,_{-22}^{+17})^\circ modulo 180180^\circ, where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8σ3.8\,\sigma evidence for CPCP violation in the interference between decay and decay after mixing.We report the measurements of the CP -violating parameters in Bs0_{s}^{0}  → Ds_{s}^{∓} K±^{±} decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb1^{−1} recorded with the LHCb detector. We measure Cf_{f} = 0.73 ± 0.14 ± 0.05, AfΔΓ_{f}^{ΔΓ}  = 0.39 ± 0.28 ± 0.15, AfΔΓ=0.31±0.28±0.15 {A}_{\overline{f}}^{\varDelta \varGamma }=0.31\pm 0.28\pm 0.15 , Sf_{f} = −0.52 ± 0.20 ± 0.07, Sf=0.49±0.20±0.07 {S}_{\overline{f}}=-0.49\pm 0.20\pm 0.07 , where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the Bs0_{s}^{0} mixing phase, −2βs_{s} , to obtain a measurement of the CKM angle γ from Bs0_{s}^{0}  → Ds_{s}^{∓} K±^{±} decays, yielding γ = (12822+17_{− 22}^{+ 17} )° 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 mixing

    Measurement of the electron reconstruction efficiency at LHCb

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    The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb−1 of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B+→ J/ψ(e+e−)K+ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below 1%
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