2,103 research outputs found

    Measurement of C P Violation in the Decay B + → K + π 0

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    A measurement of CP violation in the decay B+→K+π0 is reported using data corresponding to an integrated luminosity of 5.4  fb−1 collected with the LHCb experiment at a center-of-mass energy of √s=13  TeV. The CP asymmetry is measured to be 0.025±0.015±0.006±0.003, where the uncertainties are statistical, systematic, and due to an external input. This is the most precise measurement of this quantity. It confirms and significantly enhances the observed anomalous difference between the direct CP asymmetries of the B0→K+π− and B+→K+π0 decays, known as the Kπ puzzle

    Study of B0s → J/ψπ+π−K+K− decays

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    The decays B0sBs0 → J/ψπ+π−K+K− are studied using a data set corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The decays B0sBs0 → J/ψK∗0K¯¯¯¯∗0J/ψK∗0K¯∗0 and B0sBs0 → χc1(3872)K+K−, where the K+K−pair does not originate from a ϕ meson, are observed for the first time. Precise measurements of the ratios of branching fractions between intermediate χc1(3872)ϕ, J/ψK∗0K¯¯¯¯∗0J/ψK∗0K¯∗0, ψ(2S)ϕ and χc1(3872)K+K− states are reported. A structure, denoted as X(4740), is observed in the J/ψϕ mass spectrum and, assuming a Breit-Wigner parameterisation, its mass and width are determined to be mX(4740)=4741±6±6MeV/c2,ΓX(4740)=53±15±11MeV,mX(4740)=4741±6±6MeV/c2,ΓX(4740)=53±15±11MeV, where the first uncertainty is statistical and the second is systematic. In addition, the most precise single measurement of the mass of the B0sBs0 meson is performed and gives a value of mB0s=5366.98±0.07±0.13MeV/c2

    Simultaneous determination of CKM angle γ and charm mixing parameters

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    A combination of measurements sensitive to the CP violation angle γ of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between D0 and D¯¯¯¯D¯0 mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN’s Large Hadron Collider, are combined for the first time. This method provides an improvement on the precision of the charm mixing parameter y by a factor of two with respect to the current world average. The charm mixing parameters are determined to be x=(0.400+0.052−0.053)%x=(0.400−0.053+0.052)% and y = (0.630+0.033−0.030)%(0.630−0.030+0.033)%. The angle γ is found to be γ = (65.4+3.8−4.2)∘(65.4−4.2+3.8)∘ and is the most precise determination from a single experiment

    Angular analysis of B0→D∗−D∗+s with D∗+s→D+sγ decays

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    The first full angular analysis of the B0 -> D-Ds+ decay is performed using 6 fb(-1) of pp collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The Ds+-> Ds+gamma and D*- -> D0- vector meson decays are used with the subsequent Ds+ -> K+K-pi (+) and D0 -> K+pi (-) decays. All helicity amplitudes and phases are measured, and the longitudinal polarisation fraction is determined to be f(L) = 0.578 +/- 0.010 +/- 0.011 with world-best precision, where the first uncertainty is statistical and the second is systematic. The pattern of helicity amplitude magnitudes is found to align with expectations from quark-helicity conservation in B decays. The ratio of branching fractions [B(B0 -> D-Ds+) x B(Ds+-> Ds+gamma)]/B(B-0 -> D(*-)Ds+) is measured to be 2.045 +/- 0.022 +/- 0.071 with world-best precision. In addition, the first observation of the Cabibbo-suppressed B-s -> D(*-)Ds+ decay is made with a significance of seven standard deviations. The branching fraction ratio B(B-s -> D(*-)Ds+)/B(B-0 -> D(*-)Ds+) is measured to be 0.049 +/- 0.006 +/- 0.003 +/- 0.002, where the third uncertainty is due to limited knowledge of the ratio of fragmentation fractions.</graphi

    Observation of a new Ξ 0 b state

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    Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5  fb−1, the observation of a new excited Ξ0b resonance decaying to the Ξ−bπ+ final state is presented. The state, referred to as Ξb(6227)0, has a measured mass and natural width of m(Ξb(6227)0)=6227.1+1.4−1.5±0.5  MeV and Γ(Ξb(6227)0)=18.6+5.0−4.1±1.4  MeV, where the uncertainties are statistical and systematic. The production rate of the Ξb(6227)0 state relative to that of the Ξ−b baryon in the kinematic region 2<η<5 and pT<30  GeV is measured to be fΞb(6227)0fΞ−bB(Ξb(6227)0→Ξ−bπ+)=0.045±0.008±0.004, where B(Ξb(6227)0→Ξ−bπ+) is the branching fraction of the decay, and fΞb(6227)0 and fΞ−b represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed Ξb(6227)− state, along with the mass of the Ξ−b baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values

    Centrality determination in heavy-ion collisions with the LHCb detector

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    The centrality of heavy-ion collisions is directly related to the created medium in these interactions. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at √s NN = 5 TeV and lead-neon fixed-target collisions at √s NN = 69 GeV. The energy deposits in the electromagnetic calorimeter are used to determine and define the centrality classes. The correspondence between the number of participants and the centrality for the lead-lead collisions is in good agreement with the correspondence found in other experiments, and the centrality measurements for the lead-neon collisions presented here are performed for the first time in fixed-target collisions at the LHC

    Amplitude analysis of the B + → D + D − K + decay

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    Results are reported from an amplitude analysis of the B+→D+D−K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at √s=7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D−K+ channel with masses around 2.9  GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2 χc2(3930) state

    Precise determination of the Bs0 – B¯s0 oscillation frequency

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    Mesons comprising a beauty quark and strange quark can oscillate between particle (Bs0) and antiparticle (B¯s0) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δms. Here we present a measurement of Δms using Bs0→Ds−π+ decays produced in proton–proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be Δms = 17.7683 ± 0.0051 ± 0.0032 ps−1, where the first uncertainty is statistical and the second is systematic. This measurement improves on the current Δms precision by a factor of two. We combine this result with previous LHCb measurements to determine Δms = 17.7656 ± 0.0057 ps−1, which is the legacy measurement of the original LHCb detector

    Angular Analysis of the B + → K * + μ + μ − Decay

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    We present an angular analysis of the B+ -> K*(+)(-> K-S(0)pi(+))mu(+) mu(-) decay using 9 fb(-1) of pp collision data collected with the LHCb experiment. For the first time, the full set of CP-averaged angular observables is measured in intervals of the dimuon invariant mass squared. Local deviations from standard model predictions are observed, similar to those in previous LHCb analyses of the isospin-partner B-0 -> K*(0)mu(+)mu(-) decay. The global tension is dependent on which effective couplings are considered and on the choice of theory nuisance parameters

    Measurement of the prompt-production cross-section ratio σ ( χ c 2 ) / σ ( χ c 1 ) in p Pb collisions at √ s N N = 8.16 TeV

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    This article reports the first measurement of prompt chi(c1) and chi(c2) charmonium production in nuclear collisions at Large Hadron Collider energies. The cross-section ratio sigma(chi(c2))/sigma(chi(c1)) is measured in pPb collisions at root s(NN) = 8.16 TeV, collected with the LHCb experiment. The chi(c1,2) states are reconstructed via their decay to a J/psi meson, subsequently decaying into a pair of oppositely charged muons, and a photon, which is reconstructed in the calorimeter or via its conversion in the detector material. The cross-section ratio is consistent with unity in the two considered rapidity regions. Comparison with a corresponding cross-section ratio previously measured by the LHCb Collaboration in pp collisions suggests that chi(c1) and chi(c2) states are similarly affected by nuclear effects occurring in pPb collisions
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