30 research outputs found

    Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

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    Contains fulltext : 121524.pdf (preprint version ) (Open Access

    Search for Charged Higgs bosons: Combined Results Using LEP Data

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    The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for pair-produced charged Higgs bosons in the framework of Two Higgs Doublet Models (2HDMs). The data of the four experiments are statistically combined. The results are interpreted within the 2HDM for Type I and Type II benchmark scenarios. No statistically significant excess has been observed when compared to the Standard Model background prediction, and the combined LEP data exclude large regions of the model parameter space. Charged Higgs bosons with mass below 80 GeV/c^2 (Type II scenario) or 72.5 GeV/c^2 (Type I scenario, for pseudo-scalar masses above 12 GeV/c^2) are excluded at the 95% confidence level

    Identification of beauty and charm quark jets at LHCb

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    Identification of jets originating from beauty and charm quarks is important for measuring Standard Model processes and for searching for new physics. The performance of algorithms developed to select b- and c-quark jets is measured using data recorded by LHCb from proton-proton collisions at √s = 7 TeV in 2011 and at √s = 8 TeV in 2012. The efficiency for identifying a b(c) jet is about 65%(25%) with a probability for misidentifying a light-parton jet of 0.3% for jets with transverse momentum p(T) > 20GeV and pseudorapidity 2.2 < η < 4.2. The dependence of the performance on the p(T) and η of the jet is also measured

    Precision measurement of the ratio of the Lambda(0)(b) to (B)over-bar(0) lifetimes

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    The LHCb measurement of the lifetime ratio of the Lambda(0)(b) baryon to the (B) over bar (0) meson is updated using data corresponding to an integrated luminosity of 3.0 fb(-1) collected using 7 and 8 TeV centre-of-mass energy pp collisions at the LHC. The decay modes used are Lambda(0)(b) -> J/psi pK(-) and (B) over bar (0) -> J/psi pi K-+(-), where the pi K-+(-) mass is consistent with that of the (K) over bar*(0)(892) meson. The lifetime ratio is determined with unprecedented precision to be 0.974 +/- 0.006 +/- 0.004, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the (B) over bar (0) lifetime, the Lambda(0)(b) lifetime is found to be 1.479 +/- 0.009 +/- 0.010 ps. (C) 2014 The Authors. Published by Elsevier B.V

    A study of CP violation in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays with D -> (KSK +/-)-K-0 pi(-/+) final states

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    A first study of CP violation in the decay modes B-+/- -> [(KSK +/-)-K-0 pi(-/+)](D)h(+/-) and B-+/- -> [(KSK +/-)-K-0 pi(-/+)](D)h(+/-), where h labels a K or pi meson and D labels a D-0 or (D) over bar (0) meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb(-1). The analysis is sensitive to the CP-violating CKM phase gamma through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of gamma using other decay modes. (C) 2014 The Authors. Published by Elsevier B.V

    Determination of gamma and-2 beta(s) from charmless two-body decays of beauty mesons

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    Using the latest LHCb measurements of time-dependent CP violation in the B-s(0) -> K+K- decay, a U-spin relation between the decay amplitudes of B-s(0) -> K+K- and B-0 -> p(+)p(-) decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B-s(0) mixing phase -2 beta(s). Results from an extended approach, which uses additional inputs on B-0 -> pi(0)pi(0) and B+ -> pi(+)pi(0) decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of U-spin breaking is studied. At 68% probability, the value gamma =( 63.5(-6.7)(+7.2))degrees modulo 180 degrees is determined. In an alternative analysis, the value -2 beta(s)= - 0.12(-0.16)(+ 0.14) rad is found. In both measurements, the uncertainties due to U-spin breaking effects up to 50% are included. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/)

    Measurement of CP violation and constraints on the CKM angle gamma in B-+/- -> DK +/- with D -> K-s(0)pi(+)pi(-) decays

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    A model-dependent amplitude analysis of B-+/- -> DK +/- with D -> K-s(0)pi(+)pi(-) decays is performed using proton proton collision data, corresponding to an integrated luminosity of 1 fb(-1), recorded by LHCb at a centre-of-mass energy of 7 TeV in 2011. Values of the CP violation observables x +/- and y +/-, which are sensitive to the CKM angle gamma, are measured to be x- = +0.027 +/- 0.0441(-0.008)(+0.010) +/- 0.001, y- = +0.013 +/- 0.0481(-0.007)(+0.009) +/- 0.003, x+ = -0.084 +/- 0.045 +/- 0.009 +/- 0.005, y+ = -0.032 +/- 0.048(-0.009)(+0.010) +/- 0.008, where the first uncertainty is statistical, the second systematic and the third arises from the uncertainty of the D -> K-S(0)pi(+)pi(-) amplitude model. The value of gamma is determined to be (84(-42)(+49))degrees including all sources of uncertainty. Neutral D meson mixing is found to have negligible effect. (C) 2014 The Authors. Published by Elsevier B.V

    Measurement of the (B)over-bar(0)-B-0 and (B)over-bars(0)-B-s(0) production asymmetries in pp collisions at root s=7 TeV

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    The (B) over bar (0)-B-0 and (B) over bar (0)(s)-B-s(0) production asymmetries, A(P)(B-0) and A(P)(B-s(0)), are measured by means of a time-dependent analysis of B-0 -> J/Psi K-*0, B-0 -> D-pi(+) and B-s(0) -> D-s(-)pi(+) decays, using a data sample corresponding to an integrated luminosity of 1.0 fb(-1), collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the B-0 and B-s(0) mesons within the LHCb acceptance. The production asymmetries, integrated over p(T) and eta in the range 4 < p(T) < 30 GeV/c and 2.5 < eta < 4.5, are determined to be A(P)(B-0) = (-0.35 +/- 0.76 +/- 0.28)% and A(P)(B-s(0)) = (1.09 +/- 2.61 +/- 0.66)%, where the first uncertainties are statistical and the second systematic. (C) 2014 The Authors. Published by Elsevier B.V

    Measurement of the CP-violating phase phi(s) in (B)over-bar(s)(0) -> J / psi pi(+)pi(-) decays

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    The mixing-induced CP-violating phase phi(s) in B-s(0) and (B) over bar (0)(s) decays is measured using the J / psi pi(+)pi(-) final state in data, taken from 3 fb(-1) of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centre-of-mass pp collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct CP violation, yields a value for the phase phi(s) = 70 +/- 68 +/- 8 mrad. This result is consistent with the Standard Model expectation and previous measurements. (C) 2014 The Authors. Published by Elsevier B.V

    Measurement of the track reconstruction efficiency at LHCb

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    The determination of track reconstruction efficiencies at LHCb using J/psi -> mu(+)mu(-) decays is presented. Efficiencies above 95% are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of 0.8% for data taking in 2010, and at a precision of 0.4% for data taking in 2011 and 2012. For hadrons an additional 1.4% uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb
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