8 research outputs found

    Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV

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    Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decreas

    Measurement of the CKM angle Îł using the B± → D*h± channels

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    A measurement of the CP-violating observables from B± → D*K± and B± → D*π± decays is presented, where D*(D) is an admixture of D*0 and D¯∗0 (D0 and DÂŻ0) states and is reconstructed through the decay chains D*→ Dπ0/Îł and D→KS0π+π−/KS0K+K−. The measurement is performed by analysing the signal yield variation across the D decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fb−1 at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle Îł is determined to be 69−14+13∘ using the measured CP-violating observables. The hadronic parameters rBD∗K±, rBD∗π±, ÎŽBD∗K±, ÎŽBD∗π±, which are the ratios and strong phase differences between favoured and suppressed B± decays, are also reported

    Measurement of prompt D+ and Ds+ production in pPb collisions at √sNN = 5. 02 TeV

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    The production of prompt D+ and D+s mesons is studied in proton-lead collisions at a centre-of-mass energy of √sNN = 5.02 TeV. The data sample corresponding to an integrated luminosity of (1.58 ± 0.02)nb−1 is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D+ and D+s candidates with transverse momentum in the range of 0 < pT < 14 GeV/c and rapidities in the ranges of 1.5 < y∗ < 4.0 and –5.0 < y∗ < –2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D+, D+s and D0 mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies

    Observation of New Baryons in the Ξ_{b}^{-}π^{+}π^{-} and Ξ_{b}^{0}π^{+}π^{-} Systems.

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    The first observation and study of two new baryonic structures in the final state Ξ_{b}^{0}π^{+}π^{-} and the confirmation of the Ξ_{b}(6100)^{-} state in the Ξ_{b}^{-}π^{+}π^{-} decay mode are reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9  fb^{-1}. In addition, the properties of the known Ξ_{b}^{*0}, Ξ_{b}^{'-} and Ξ_{b}^{*-} resonances are measured with improved precision. The new decay mode of the Ξ_{b}^{0} baryon to the Ξ_{c}^{+} π^{-} π^{+} π^{-} final state is observed and exploited for the first time in these measurements

    Search for the baryon- and lepton-number violating decays <math display="inline"><msup><mi>B</mi><mn>0</mn></msup><mo stretchy="false">→</mo><mi>p</mi><msup><mi>ÎŒ</mi><mo>-</mo></msup></math> and <math display="inline"><msubsup><mi>B</mi><mi>s</mi><mn>0</mn></msubsup><mo stretchy="false">→</mo><mi>p</mi><msup><mi>ÎŒ</mi><mo>-</mo></msup></math>

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    International audienceA search for the baryon- and lepton-number violating decays B0→pÎŒ- and Bs0→pÎŒ- is performed at the LHCb experiment using data collected in proton-proton collisions at s=7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2, and 6  fb-1, respectively. No significant signal for B0→pÎŒ- and Bs0→pÎŒ- decays is found and the upper limits on the branching fractions are determined to be B(B0→pÎŒ-)&lt;2.6(3.1)×10-9 and B(Bs0→pÎŒ-)&lt;12.1(14.0)×10-9, respectively, at 90% (95%) confidence level. These are the first limits on these decays to date

    Search for a light charged Higgs boson decaying to c-sbar in pp collisions at sqrt(s) = 8 TeV

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    see paper for full list of authorsInternational audienceA search for a light charged Higgs boson, originating from the decay of a top quark and subsequently decaying into a charm quark and a strange antiquark, is presented. The data used in the analysis correspond to an integrated luminosity of 19.7 inverse-femtobarns recorded in proton-proton collisions at sqrt(s) = 8 TeV by the CMS experiment at the LHC. The search is performed in the process t tbar to W+/- b H-/+ bbar, where the W boson decays to a lepton (electron or muon) and a neutrino. The decays lead to a final state comprising an isolated lepton, at least four jets and large missing transverse energy. No significant deviation is observed in the data with respect to the standard model predictions, and model-independent upper limits are set on the branching fraction BF( t to H+ b ), ranging from 1.2 to 6.5% for a charged Higgs boson with mass between 90 and 160 GeV, under the assumption that BF( H+ to c sbar ) = 100%

    Measurement of the ratio B(tâ€șWb)/B(tâ€șWq) in pp collisions at s=8 TeV

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    The ratio of the top-quark branching fractions R=B(tâ€șWb)/B(tâ€șWq), where the denominator includes the sum over all down-type quarks (q=b,s,d), is measured in the ttÂŻ dilepton final state with proton–proton collision data at s=8 TeV from an integrated luminosity of 19.7 fb-1, collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R=1.014±0.003(stat.)±0.032(syst.) is measured, in a good agreement with current precision measurements in electroweak and flavour sectors. A lower limit R&gt;0.955 at the 95% confidence level is obtained after requiring R?1, and a lower limit on the Cabibbo–Kobayashi–Maskawa matrix element |Vtb|&gt;0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, ?t=1.36±0.02(stat.)-0.11 +0.14(syst.) GeV. © 2014 The Author

    Observation of B(s)0→J/ψpp‟B^0_{(s)} \to J/\psi p \overline{p} decays and precision measurements of the B(s)0B^0_{(s)} masses

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    International audienceThe first observation of the decays B(s)0→J/ψppÂŻ is reported, using proton-proton collision data corresponding to an integrated luminosity of 5.2  fb-1, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are B(B0→J/ψppÂŻ)=[4.51±0.40(stat)±0.44(syst)]×10-7, B(Bs0→J/ψppÂŻ)=[3.58±0.19(stat)±0.39(syst)]×10-6. For the Bs0 meson, the result is much higher than the expected value of O(10-9). The small available phase space in these decays also allows for the most precise single measurement of both the B0 mass as 5279.74±0.30(stat)±0.10(syst)  MeV and the Bs0 mass as 5366.85±0.19(stat)±0.13(syst)  MeV
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