LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Identification of beauty and charm quark jets at LHCb. J. Instrum., 10, P06013–29pp.
Abstract: 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 root s = 7TeV in 2011 and at root s = 8TeV 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 pT > 20GeV and pseudorapidity 2 : 2 < eta < 4.2. The dependence of the performance on the pT and eta of the jet is also measured.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of the B-0 -> rho(0)rho(0) decay from an amplitude analysis of B-0 -> (pi(+)pi(-))(pi(+)pi(-)) decays. Phys. Lett. B, 747, 468–478.
Abstract: Proton-proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb(-1), are analysed to search for the charmless B-0 -> rho(0)rho(0) decay. More than 600 B-0 -> (pi(+)pi(-))(pi(+)pi(-)) signal decays are selected and used to perform an amplitude, analysis, under the assumption of no CP violation in the decay, from which the B-0 -> rho(0)rho(0) decay is observed for the first time with 7.1 standard deviations significance. The fraction of B-0 -> rho(0)rho(0) decays yielding a longitudinally polarised final state is measured to be f(L) = 0.745(-0.058)(+0.048)(stat) +/- 0.034(syst). The B-0 -> rho(0)rho(0) branching fraction, using the B-0 -> phi K*(892)(0) decay as reference, is also reported as B(B-0 -> rho(0)rho(0)) = (0.94 +/- 0.17(stat) +/- 0.09(syst) +/- 0.06(BF)) x 10(-6).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of the decay (B)over-bar(s)(0) -> psi(2S)K+pi(-). Phys. Lett. B, 747, 484–494.
Abstract: The decay (B) over bar (0)(s) -> psi(2S)K+pi(-) is observed using a data set corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. The branching fraction relative to the B-0 -> psi(2S)K+pi(-) decay mode is measured to be B((B) over bar (0)(s) -> psi(2S)K+pi(-))/B(B-0 -> psi(2S)K+pi(-)) = 5.38 +/- 0.36 (stat) +/- 0.22 (syst) +/- 0.31 (f(s)/f(d)) %, where f(s)/f(d) indicates the uncertainty due to the ratio of probabilities for a b quark to hadronise into a B-s(0) or B-0 meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate K*(892)(0) meson is measured to be 0.645 +/- 0.049 (stat) +/- 0.049 (syst) and its longitudinal polarisation fraction is 0.524 +/- 0.056 (stat) +/- 0.029 (syst). The relative branching fraction for this component is determined to be B((B) over bar (0)(s) -> psi(2S)K*(892)(0))/B(B-0 -> psi(2S)K*(892)(0)) = 5.58 +/- 0.57 (stat) +/- 0.40 (syst) +/- 0.32 (f(s)/f(d)) %. In addition, the mass splitting between the B-s(0) and B-0 mesons is measured as M(B-s(0)) – M(B-0) = 87.45 +/- 0.44 (stat) +/- 0.09 (syst) MeV/c(2).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). B flavour tagging using charm decays at the LHCb experiment. J. Instrum., 10, P10005–16pp.
Abstract: An algorithm is described for tagging the flavour content at production of neutral B mesons in the LHCb experiment. The algorithm exploits the correlation of the flavour of a B meson with the charge of a reconstructed secondary charm hadron from the decay of the other b hadron produced in the proton-proton collision. Charm hadron candidates are identified in a number of fully or partially reconstructed Cabibbo-favoured decay modes. The algorithm is calibrated on the self-tagged decay modes B+ -> J/psi K+ and B-0 -> J/psi K*(0) using 3.0fb(-1) of data collected by the LHCb experiment at pp centre-of-mass energies of 7TeV and 8TeV. Its tagging power on these samples of B -> J/psi X decays is (0.30 +/- 0.01 +/- 0.01) %.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Search for the lepton-flavour violating decay D-0 -> e(+/-)mu(-/+). Phys. Lett. B, 754, 167–175.
Abstract: A search for the lepton-flavour violating decay D-0 -> e(+/-)mu(-/+) is made with a dataset corresponding to an integrated luminosity of 3.0 fb(-1) of proton-proton collisions at centre-of-mass energies of 7 TeV and 8 TeV, collected by the LHCb experiment. Candidate D-0 mesons are selected using the decay D*(+) -> D-0 pi(+) and the D-0 -> e(+/-)mu(+) branching fraction is measured using the decay mode D-0 -> K-pi(+) as a normalization channel. No significant excess of D-0 -> e(+/-)mu(-/+) candidates over the expected background is seen, and a limit is set on the branching fraction, B(D-0 -> e(+/-)mu(-/+)) < 1.3 x10(-8), at 90% confidence level. This is an order of magnitude lower than the previous limit and it further constrains the parameter space in some leptoquark models and in supersymmetric models with R-parity violation.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First observation of the decay D-0 -> K-pi(+)mu(+)mu(-) in the rho(0)-omega region of the dimuon mass spectrum. Phys. Lett. B, 757, 558–567.
Abstract: A study of the decay D-0 -> K-pi(+)mu(+)mu(-) is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb(-1). Decay candidates with muon pairs that have an invariant mass in the range 675-875 MeV/c(2) are considered. This region is dominated by the rho(0) and omega resonances. The branching fraction in this range is measured to be B(D-0 -> K-pi(+)mu(+)mu(-)) = (4.17 +/- 0.12 (stat) +/- 0.40 (syst)) x 10(-6). This is the first observation of the decay D-0 -> K-pi(+)mu(+)mu(-). Its branching fraction is consistent with the value expected in the Standard Model.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). A new algorithm for identifying the flavour of B-s(0) mesons at LHCb. J. Instrum., 11, P05010–23pp.
Abstract: A new algorithm for the determination of the initial flavour of B-s(0) mesons is presented. The algorithm is based on two neural networks and exploits the b hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the B-s(0) meson. The second network combines the kaon charges to assign the B-s(0) flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb(-1) collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the B-s(0)-B-s(0) flavour oscillations in B-s(0) -> D-s(-)pi(+) decays, and by analysing flavour-specific B-s2*(5840)(0) -> B+K- decays. The tagging power measured in B-s(0) -> D-s(-)pi(+) decays is found to be (1.80 +/- 0.19 ( stat) +/- 0.18 (syst))%, which is an improvement of about 50% compared to a similar algorithm previously used in the LHCb experiment.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of CP observables in B +/- -> DK +/- and B +/- -> D pi +/- with two- and four-body D decays. Phys. Lett. B, 760, 117–131.
Abstract: Measurements of CP observables in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays are presented where the D meson is reconstructed in the final states K-+/-pi(-/+), pi K-+/-(-/+), K+K-, pi(+)pi(-), K-+/-pi(-/+)pi(+)pi(-), pi K-+/-(-/+)pi(+)pi(-) and pi(+)pi(-)pi(+)pi(-). This analysis uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb(-1). Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle gamma. The analysis of the four-pion D decay mode is the first of its kind.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Observation of the Lambda(0)(b) -> Lambda phi decay. Phys. Lett. B, 759, 282–292.
Abstract: The Lambda(0)(b) -> Lambda phi decay is observed using data corresponding to an integrated luminosity of 3.0 fb(-1) recorded by the LHCb experiment. The decay proceeds at leading order via a b -> s<(s)double over bar>s loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of 5.9 standard deviations. The value of the branching fraction is measured to be (5.18 +/- 1.04 +/- 0.35(-0.62)(+0.67)) x 10(-6), where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Search for B-c(+) decays to the p(p)over-bar pi(+) final state. Phys. Lett. B, 759, 313–321.
Abstract: A search for the decays of the B-c(+) meson to p (p) over bar pi(+) is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, f(c)/f(u) x B(B-c(+) -> p (p) over bar pi(+)) < 3.6 x 10(-8) in the kinematic region m(p<(p)over bar>) < 2.85 GeV/c(2), p(T)(B) < 20 GeV/c and 2.0 < y(B) < 4.5, where B is the branching fraction and f(c)(f(u)) is the fragmentation fraction of the b quark into a B-c+(B+) meson.
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