202 research outputs found

    Study of bb-hadron decays to Λc+hh\Lambda_c^+h^-h^{\prime -} final states

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    Decays of Ξb\Xi_{b}^{-} and Ωb\Omega_{b}^{-} baryons to Λc+hh\Lambda_{c}^{+} h^- h^{\prime -} final states, with hhh^- h^{\prime -} being ππ\pi^{-}\pi^{-}, KπK^{-}\pi^{-} and KKK^{-}K^{-} meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7fb18.7 \rm fb^{-1} of pppp collisions collected at centre-of-mass energies s=7\sqrt{s} = 7, 88 and 13TeV13 \rm TeV. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the BΛc+pˉπB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} \pi^{-} mode, are measured, with ΞbΛc+Kπ\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} \pi^{-}, ΞbΛc+KK\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} K^{-} and ΩbΛc+KK\Omega_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} K^{-} decays being observed at over 5σ5\,\sigma significance. The ΞbΛc+Kπ\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} \pi^{-} mode is also used to measure the Ξb\Xi_{b}^{-} production asymmetry, which is found to be consistent with zero. In addition, the BΛc+pˉKB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} K^{-} decay is observed for the first time, and its branching fraction is measured relative to that of the BΛc+pˉπB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} \pi^{-} mode.Decays of Ξb\Xi_b^- and Ωb\Omega_b^- baryons to Λc+hh\Lambda_c^+ h^- h^{\prime -} final states, with hhh^- h^{\prime -} being ππ\pi^-\pi^-, KπK^-\pi^- and KKK^-K^- meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7fb18.7\,\mathrm{fb}^{-1} of pppp collisions collected at centre-of-mass energies s=7\sqrt{s} = 7, 88 and 13TeV13\,\mathrm{Te\kern -0.1em V}. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the BΛc+pπB^- \to \Lambda_c^+ \overline{p} \pi^- mode, are measured, with ΞbΛc+Kπ\Xi_{b}^- \to\Lambda_{c}^+ K^- \pi^-, ΞbΛc+KK\Xi_{b}^- \to\Lambda_{c}^+ K^- K^- and ΩbΛc+KK\Omega_{b}^- \to\Lambda_{c}^+ K^- K^- decays being observed at over 5σ5\,\sigma significance. The ΞbΛc+Kπ\Xi_{b}^- \to\Lambda_{c}^+ K^- \pi^- mode is also used to measure the Ξb\Xi_{b}^- production asymmetry, which is found to be consistent with zero. In addition, the BΛc+pKB^- \to \Lambda_{c}^+ \overline{p} K^- decay is observed for the first time, and its branching fraction is measured relative to that of the BΛc+pπB^- \to \Lambda_{c}^+ \overline{p} \pi^- mode

    Improved measurement of CPCP violation parameters in Bs0J/ψK+KB_s^0\to J/\psi K^+K^- decays in the vicinity of the ϕ(1020)\phi(1020) resonance

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    The decay-time-dependent CPCP asymmetry in Bs0J/ψ(μ+μ)K+KB_s^0\to J/\psi(\to \mu^+\mu^-) K^+ K^- decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6fb16 {\rm fb}^{-1}, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 Bs0B_s^0 signal decays with an invariant K+KK^+ K^- mass in the vicinity of the ϕ(1020)\phi(1020) resonance, the CPCP-violating phase ϕs\phi_s is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0B_s^0-Bs0\overline{B}_s^0 system, ΔΓs\Delta\Gamma_s, and the difference of the average Bs0B_s^0 and B0B^0 meson decay widths, ΓsΓd\Gamma_s-\Gamma_d. The values obtained are ϕs=0.039±0.022±0.006\phi_s = -0.039 \pm 0.022 \pm 0.006 rad, ΔΓs=0.0845±0.0044±0.0024 ps1\Delta\Gamma_s = 0.0845 \pm 0.0044 \pm 0.0024 ~{\rm ps}^{-1} and ΓsΓd=0.0560.0015+0.0013±0.0014 ps1\Gamma_s-\Gamma_d = -0.056^{\:+\:0.0013}_{\:-\:0.0015} \pm 0.0014 ~{\rm ps}^{-1}, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕs\phi_s is also measured independently for each polarization state of the K+KK^+K^- system and shows no evidence for polarization dependence.The decay-time-dependent CPCP asymmetry in Bs0J/ψ(μ+μ)K+KB^0_s\to J/\psi(\to \mu^{+}\mu^{-}) K^{+}K^{-} decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb1fb^{-1}, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 Bs0B^{0}_{s} signal decays with an invariant K+KK^{+}K^{-} mass in the vicinity of the ϕ(1020)\phi(1020) resonance, the CPCP-violating phase ϕs\phi_s is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0B^0_s-Bˉs0\bar{B}^0_s system, ΔΓs\Delta\Gamma_s, and the difference of the average Bs0B^0_s and B0B^0 meson decay widths, ΓsΓd\Gamma_s-\Gamma_d. The values obtained are ϕs= 0.039±0.022±0.006\phi_s = \ -0.039 \pm 0.022 \pm 0.006 rad, ΔΓs=0.0845±0.0044±0.0024\Delta\Gamma_s = 0.0845 \pm 0.0044 \pm 0.0024 ps1^{-1} and ΓsΓd=0.00560.0015+0.0013±0.0014\Gamma_s-\Gamma_d = -0.0056 ^{+ 0.0013}_{-0.0015} \pm 0.0014 ps1^{-1}, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕs\phi_s is also measured independently for each polarization state of the K+KK^{+}K^{-} system and shows no evidence for polarization dependence

    Search for Bc+π+μ+μB_c^+\to\pi^+\mu^+\mu^- decays and measurement of the branching fraction ratio B(Bc+ψ(2S)π+)/B(Bc+J/ψπ+){\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+)

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    International audienceThe first search for nonresonant Bc+π+μ+μB_c^+\to\pi^+\mu^+\mu^- decays is reported. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb1^{-1}. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio B(Bc+π+μ+μ)/B(Bc+J/ψπ+)<2.1×104{\cal B}(B_c^+\to\pi^+\mu^+\mu^-)/{\cal B}(B_c^+\to J/\psi \pi^+) < 2.1\times 10^{-4} at 90%90\% confidence level. Additionally, an updated measurement of the ratio of the Bc+ψ(2S)π+B_c^+\to\psi(2S)\pi^+ and Bc+J/ψπ+B_c^+\to J/\psi \pi^+ branching fractions is reported. The ratio B(Bc+ψ(2S)π+)/B(Bc+J/ψπ+){\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+) is measured to be 0.254±0.018±0.003±0.0050.254\pm 0.018 \pm 0.003 \pm 0.005, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic J/ψJ/\psi and ψ(2S)\psi(2S) decays. This measurement is the most precise to date and is consistent with previous LHCb results

    Helium identification with LHCb

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    International audienceThe identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pppp collision data at s=13TeV\sqrt{s}=13\,{\rm TeV} recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5fb15.5\,{\rm fb}^{-1}. A total of around 10510^5 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50%50\% with a corresponding background rejection rate of up to O(1012)\mathcal O(10^{12}). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei

    Observation of Cabibbo-suppressed two-body hadronic decays and precision mass measurement of the Ωc0\Omega_{c}^{0} baryon

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    International audienceThe first observation of the singly Cabibbo-suppressed Ωc0ΩK+\Omega_{c}^{0}\to\Omega^{-}K^{+} and Ωc0Ξπ+\Omega_{c}^{0}\to\Xi^{-}\pi^{+} decays is reported, using proton-proton collision data at a centre-of-mass energy of 13TeV13\,{\rm TeV}, corresponding to an integrated luminosity of 5.4fb15.4\,{\rm fb}^{-1}, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be B(Ωc0ΩK+)B(Ωc0Ωπ+)=0.0608±0.0051(stat)±0.0040(syst)\frac{\mathcal{B}(\Omega_{c}^{0}\to\Omega^{-}K^{+})}{\mathcal{B}(\Omega_{c}^{0}\to\Omega^{-}\pi^{+})}=0.0608\pm0.0051({\rm stat})\pm 0.0040({\rm syst}), B(Ωc0Ξπ+)B(Ωc0Ωπ+)=0.1581±0.0087(stat)±0.0043(syst)±0.0016(ext)\frac{\mathcal{B}(\Omega_{c}^{0}\to\Xi^{-}\pi^{+})}{\mathcal{B}(\Omega_{c}^{0}\to\Omega^{-}\pi^{+})}=0.1581\pm0.0087({\rm stat})\pm0.0043({\rm syst})\pm0.0016({\rm ext}). In addition, using the Ωc0Ωπ+\Omega_{c}^{0}\to\Omega^{-}\pi^{+} decay channel, the Ωc0\Omega_{c}^{0} baryon mass is measured to be M(Ωc0)=2695.28±0.07(stat)±0.27(syst)±0.30(ext)MeV/c2M(\Omega_{c}^{0})=2695.28\pm0.07({\rm stat})\pm0.27({\rm syst})\pm0.30({\rm ext})\,{\rm MeV}/c^{2}, improving the precision of the previous world average by a factor of four

    Measurement of CP violation in B0ψ(+)KS0(π+π)decaysB^0\to \psi(\to\ell^+\ell^-)K^0_\mathrm{S}(\to \pi^+\pi^-)decays

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    A measurement of time-dependent C ⁣PC\!P violation in the decays of B0B^0 and B0\overline{B}^0 mesons to the final states J ⁣/ ⁣ψ(μ+μ)KS0{J\!/\!\psi(\to\mu^+\mu^-)K^0_\mathrm{S}}, ψ(2S)(μ+μ)KS0\psi(2S)(\to\mu^+\mu^-)K^0_\mathrm{S} and J ⁣/ ⁣ψ(e+e)KS0J\!/\!\psi(\to e^+e^-)K^0_\mathrm{S} with KS0π+πK^0_\mathrm{S}\pi^+\pi^- is presented. The data correspond to an integrated luminosity of 6fb16\,\mathrm{fb}^{-1} collected at a centre-of-mass energy of s=13TeV\sqrt{s}=13\,\mathrm{TeV} with the LHCb detector. The C ⁣PC\!P-violation parameters are measured to be \begin{align*} S_{\psi K^0_\mathrm{S}} &= 0.717 \pm 0.013\,(\text{stat}) \pm 0.008\,(\text{syst}), \\ C_{\psi K^0_\mathrm{S}} &= 0.008 \pm 0.012\,(\text{stat}) \pm 0.003\,(\text{syst}). \end{align*} This measurement of SψKS0S_{\psi K^0_\mathrm{S}} represents the most precise single measurement of the CKM angle β\beta to date and is more precise than the current world average. In addition, measurements of the C ⁣PC\!P-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed.A measurement of time-dependent CP violation in the decays of B0B^0 and B0\overline{B}^0 mesons to the final states J/ψ(μ+μ)KS0J/\psi(\to\mu^+\mu^-)K^0_S, ψ(2S)(μ+μ)KS0\psi(2S)(\to\mu^+\mu^-)K^0_S and J/ψ(e+e)KS0J/\psi(\to e^+e^-)K^0_S with KS0π+πK^0_S\to\pi^+\pi^- is presented. The data correspond to an integrated luminosity of 6 fb1{}^{-1} collected at a centre-of-mass energy of s=13\sqrt{s}=13 TeV with the LHCb detector. The CP-violation parameters are measured to be \begin{align*} S_{\psi K^0_S} &= 0.717 \pm 0.013 (\text{stat}) \pm 0.008 (\text{syst}), \\ C_{\psi K^0_S} &= 0.008 \pm 0.012 (\text{stat}) \pm 0.003 (\text{syst}). \end{align*} This measurement of SψKS0S_{\psi K^0_S} represents the most precise single measurement of the CKM angle β\beta to date and is more precise than the current world average. In addition, measurements of the CP-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed

    Enhanced production of Λb0\Lambda_{b}^{0} baryons in high-multiplicity pppp collisions at s=13\sqrt{s} = 13 TeV

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    International audienceThe production rate of Λb0\Lambda_{b}^{0} baryons relative to B0B^{0} mesons in pppp collisions at a center-of-mass energy s=13\sqrt{s} = 13 TeV is measured by the LHCb experiment. The ratio of Λb0\Lambda_{b}^{0} to B0B^{0} production cross-sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e+ee^{+}e^{-} collisions, and increases by a factor of 2\sim2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λb0\Lambda_{b}^{0} to B0B^{0} cross-sections is higher than what is measured in e+ee^{+}e^{-} collisions, but converges with the e+ee^{+}e^{-} ratio as the momentum increases. These results imply that the evolution of heavy bb quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with a statistical hadronization model and implications for the mechanisms enforcing quark confinement are discussed

    Charge-dependent curvature-bias corrections using a pseudomass method

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    International audienceMomentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy s=13\sqrt{s}=13 TeV during 2016, 2017 and 2018. The biases are determined using Zμ+μZ\to\mu^+\mu^- decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10410^{-4} GeV1^{-1} level, improves the Zμ+μZ\to\mu^+\mu^- mass resolution by roughly 20% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass

    Search for CP\textit{CP} violation in the phase space of D0KS0K±πD^{0} \rightarrow K_{S}^{0} K^{\pm} \pi^{\mp} decays with the energy test

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    International audienceA search for CP\textit{CP} violation in D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} and D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} decays is reported. The search is performed using an unbinned model-independent method known as the energy test that probes local CP\textit{CP} violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 5.4~fb1^{-1} collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of s=13\sqrt{s}=13~TeV, amounting to approximately 950000 and 620000 signal candidates for the D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} and D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} modes, respectively. The method is validated using D0Kπ+ππ+D^{0} \rightarrow K^{-} \pi^{+} \pi^{-} \pi^{+} and D0KS0π+πD^{0} \rightarrow K_{S}^{0} \pi^{+} \pi^{-} decays, where CP\textit{CP}-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP\textit{CP} symmetry in both the D0KS0Kπ+D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} and the D0KS0K+πD^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} decays, with pp-values for the hypothesis of no CP\textit{CP} violation of 70% and 66%, respectively
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