21 research outputs found

    Measurement of the B_{s}^{0}→μ^{+}μ^{-} Branching Fraction and Effective Lifetime and Search for B^{0}→μ^{+}μ^{-} Decays.

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    A search for the rare decays B_{s}^{0}→μ^{+}μ^{-} and B^{0}→μ^{+}μ^{-} is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4  fb^{-1}. An excess of B_{s}^{0}→μ^{+}μ^{-} decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B_{s}^{0}→μ^{+}μ^{-})=(3.0±0.6_{-0.2}^{+0.3})×10^{-9}, where the first uncertainty is statistical and the second systematic. The first measurement of the B_{s}^{0}→μ^{+}μ^{-} effective lifetime, τ(B_{s}^{0}→μ^{+}μ^{-})=2.04±0.44±0.05  ps, is reported. No significant excess of B^{0}→μ^{+}μ^{-} decays is found, and a 95% confidence level upper limit, B(B^{0}→μ^{+}μ^{-})<3.4×10^{-10}, is determined. All results are in agreement with the standard model expectations

    Measurement of the B0s→μ+μ− Branching Fraction and Effective Lifetime and Search for B0→μ+μ− Decays

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    See paper for full list of authors - 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-2017-001.html - Submitted to Phys. Rev. Lett.International audienceA search for the rare decays B0s→μ+μ− and B0→μ+μ− is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb−1. An excess of B0s→μ+μ− decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B0s→μ+μ−)=(3.0±0.6+0.3−0.2)×10−9, where the first uncertainty is statistical and the second systematic. The first measurement of the B0s→μ+μ− effective lifetime, τ(B0s→μ+μ−)=2.04±0.44±0.05 ps, is reported. No significant excess of B0→μ+μ− decays is found and a 95 % confidence level upper limit, B(B0→μ+μ−)<3.4×10−10, is determined. All results are in agreement with the Standard Model expectations

    Observation of Five New Narrow Omega(0)(c) States Decaying to Xi K-+(c)-

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    The Ξc+K\Xi_c^+ K^- mass spectrum is studied with a sample of pppp collision data corresponding to an integrated luminosity of 3.3 fb1^{-1}, collected by the LHCb experiment. The Ξc+\Xi_c^+ is reconstructed in the decay mode pKπ+p K^- \pi^+. Five new, narrow excited Ωc0\Omega_c^0 states are observed: the Ωc(3000)0\Omega_c(3000)^0, Ωc(3050)0\Omega_c(3050)^0, Ωc(3066)0\Omega_c(3066)^0, Ωc(3090)0\Omega_c(3090)^0, and Ωc(3119)0\Omega_c(3119)^0. Measurements of their masses and widths are reported.Comment: 14 pages, 3 figures. 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-2017-002.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

    First measurement of the CPCP-violating phase φsddφ_s^{d\overline{d}} in Bs0(K+π)(Kπ+)B_s^0\to(K^+π^-)(K^-π^+) decays

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    A flavour-tagged decay-time-dependent amplitude analysis of Bs0(K+π)(Kπ+)B_s^0\to(K^+\pi^-)(K^-\pi^+) decays is presented in the K±πK^{\pm}\pi^{\mp} mass range from 750 to 1600 MeV/c2/c^2. The analysis uses pppp collision data collected with the LHCb detector at centre-of-mass energies of 77 and 88 TeV, corresponding to an integrated luminosity of 3.03.0 fb1^{-1}. Several quasi-two-body decay modes are considered, corresponding to K±πK^{\pm}\pi^{\mp} combinations with spin 0, 1 and 2, which are dominated by the K0(800)0K_0^*(800)^0 and K0(1430)0K_0^*(1430)^0, the K(892)0K^*(892)^0 and the K2(1430)0K_2^*(1430)^0 resonances, respectively. The longitudinal polarisation fraction for the Bs0K(892)0K(892)0B_s^0\to K^*(892)^0\overline{K}^*(892)^0 decay is measured as fL=0.208±0.032±0.046f_L=0.208 \pm 0.032 \pm 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CPCP-violating phase, ϕsdd\phi_s^{d\overline{d}}, in bddsb\to d\overline{d}s transitions is performed, yielding a value of ϕsdd=0.10\phi_s^{d\overline{d}}=-0.10 ±\pm 0.130.13 (stat) ±\pm 0.140.14 (syst) rad

    Measurement of the Ratio of the B-0 -> D*(-)iota(+)v(iota) and B-0 -> D*(-) mu(+)v(mu) Branching Fractions Using Three-Prong tau-Lepton Decays

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    The ratio of branching fractions R(D)B(B0Dτ+ντ)/B(B0Dμ+νμ){\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 Tev, corresponding to an integrated luminosity of 3 ~fb1^{-1}. For the first time R(D){\cal{R}}(D^{*-}) is determined using the τ\tau lepton decays with three charged pions in the final state. The B0Dτ+ντB^0 \to D^{*-} \tau^+\nu_{\tau} yield is normalized to that of the B0Dπ+ππ+B^0\to D^{*-} \pi^+\pi^-\pi^+ mode, providing a measurement of B(B0Dτ+ντ)/B(B0Dπ+ππ+)=1.97±0.13±0.18{\cal{B}}(B^0\to D^{*-}\tau^+\nu_{\tau})/{\cal{B}}(B^0\to D^{*-}\pi^+\pi^-\pi^+) = 1.97 \pm 0.13 \pm 0.18, where the first uncertainty is statistical and the second systematic. The value of B(B0Dτ+ντ)=(1.42±0.094±0.129±0.054)%{\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau}) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054)\% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B0Dμ+νμB^0 \to D^{*-} \mu^+\nu_{\mu} decay, a value of R(D)=0.291±0.019±0.026±0.013{\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B0Dμ+νμB^0\to D^{*-}\mu^+\nu_{\mu} modes. This measurement is in agreement with the Standard Model prediction and with previous results.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-2017-017.htm

    Chemical Properties

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

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    The ratios of the branching fractions of the decays Λc+pππ+\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}, Λc+pKK+\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}, and Λc+pπK+\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+} with respect to the Cabibbo-favoured Λc+pKπ+\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+} 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 fb1^{-1}: \begin{align*} \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp; = (7.44 \pm 0.08 \pm 0.18)\,\%, \\ \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp;= (1.70 \pm 0.03 \pm 0.03)\,\%, \\ \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp; = (0.165 \pm 0.015 \pm 0.005 )\,\%, \end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for B(Λc+pKπ+)\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+}), the corresponding branching fractions are \begin{align*} \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}) &amp;= (4.72 \pm 0.05 \pm 0.11 \pm 0.25) \times 10^{-3}, \\ \mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}) &amp;= (1.08 \pm 0.02 \pm 0.02 \pm 0.06) \times 10^{-3}, \\ \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}) &amp;= (1.04 \pm 0.09 \pm 0.03 \pm 0.05) \times 10^{-4}, \end{align*} where the final uncertainty is due to B(Λc+pKπ+)\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})
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