LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Test of lepton universality using B+ -> K(+)l(+)l(-) decays. Phys. Rev. Lett., 113(15), 151601–10pp.
Abstract: A measurement of the ratio of the branching fractions of the B+ -> K+mu(+)mu(-) and B+ -> K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV2/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) +/- 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2017). Measurement of the shape of the Lambda(0)(b) ->+ Lambda(+)(c) mu(-)(nu)over-bar μdifferential decay rate. Phys. Rev. D, 96(11), 112005–15pp.
Abstract: A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay Lambda(0)(b) ->+ Lambda(+)(c) mu(-) is reported, using data corresponding to 3 fb(-1) collected with the LHCb detector in proton-proton collisions. The Lambda(+)(c) mu(-)(nu) over bar μ(+anything) final states are reconstructed through the detection of a muon and Lambda(+)(c) baryon decaying into pK(-)pi(+), and the decay Lambda(0)(b) -> Lambda(+)(c)pi(+)pi(-)mu(-)(nu) over bar μare used to determine contributions from Lambda(0)(b) -> Lambda(c)*(+)mu(-)(nu) over bar μdecays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, q(2), is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Measurement of CP asymmetry in D-0 -> K- K+ decays. Phys. Lett. B, 767, 177–187.
Abstract: A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D-0 -> K- K+ is performed using pp collision data, corresponding to an integrated luminosity of 3 fb(-1), collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D*(+) -> D-0 pi(+) and D*(-) -> (D) over bar (0)pi(-) decays. The time-integrated CP asymmetry A(CP)(K- K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D-0 -> K- pi(+), D+ -> K- pi(+) pi(+) and D+ -> (K) over bar (0)pi(+) decays used as calibration channels. It is found to be A(CP)(K- K+) = (0.14 +/- 0.15 (stat) +/- 0.10 (syst))%. A combination of this result with previous LHCb measurements yields A(CP)(K- K+) = (0.04 +/- 0.12 (stat) +/- 0.10 (syst))%, A(CP)(pi(-) pi(+)) = (0.07 +/- 0.14 (stat) +/- 0.11 (syst))%. These are the most precise measurements from a single experiment. The result for ACP(K- K+) is the most precise determination of a time-integrated CPasymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of CP violation and constraints on the CKM angle gamma in B-+/- -> DK +/- with D -> K-s(0)pi(+)pi(-) decays. Nucl. Phys. B, 888, 169–193.
Abstract: 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.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the CKM angle gamma using B (0) -> DK (*0) with D -> K-S(0) pi (+) pi (-) decays. J. High Energy Phys., 08(8), 137–30pp.
Abstract: A model-dependent amplitude analysis of the decay B (0) -> D(K (S) (0) pi (+) pi (-))K (au 0) is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1), recorded at and 8 TeV by the LHCb experiment. The CP violation observables x (+/-) and y (+/-), sensitive to the CKM angle gamma, are measured to be x- = 0.15 +/- 0.14 +/- 0.03 +/- 0.01; y- = 0.25 +/- 0.15 +/- 0.06 +/- 0.01; x+ = 0.05 +/- 0.24 +/- 0.04 +/- 0.01; y+ = 0.65(-0.23)(+0.24) +/- 0.08 +/- 0.01; where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the D -> K (S) (0) pi (+) pi (-) amplitude model. These are the most precise measurements of these observables. They correspond to gamma = (80 (- 22) (+ 21) )A degrees and , where is the magnitude of the ratio of the suppressed and favoured B (0) -> DK (+) pi (-) decay amplitudes, in a K pi mass region of +/- 50 MeV around the K (*)(892)(0) mass and for an absolute value of the cosine of the K (*0) decay angle larger than 0.4.
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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 the mass and lifetime of the Omega(-)(b) baryon. Phys. Rev. D, 93(9), 092007–12pp.
Abstract: A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb(-1) collected by LHCb at root s = 7 and 8 TeV, is used to reconstruct 63 +/- 9 Omega(-)(b) -> Omega(0)(c)pi(-), Omega(0)(c) -> pK(-)K(-)pi(+) decays. Using the Xi(-)(b) ->Xi(0)(c)pi(-), Xi(0)(c) -> pK(-)K(-)pi(+) decay mode for calibration, the lifetime ratio and the absolute lifetime of the Omega(-)(b) baryon are measured to be tau(Omega b-)/tau(Xi b-) = 1.11 +/- 0.16 +/- 0.03, tau(Omega b-) = 1.78 +/- 0.26 +/- 0.05 +/- 0.06 ps, where the uncertainties are statistical, systematic and from the calibration mode (for tau(Omega b-) only). A measurement is also made of the mass difference, m(Omega b-) – m(Xi b-), and the corresponding Omega(-)(b) mass, which yields m(Omega b-) – m(Xi b-) = 247.4 +/- 3.2 +/- 0.5 MeV/c(2), m(Omega b-) = 6045.1 +/- 3.2 +/- 0.5 +/- 0.6 MeV/c(2). These results are consistent with previous measurements.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Search for long-lived scalar particles in B+-> K+chi(mu(+) mu(-)) decays. Phys. Rev. D, 95(7), 071101–9pp.
Abstract: A search for a long-lived scalar particle. is performed, looking for the decay B+ -> K+chi with chi ->mu(+)mu(-) pp collision data corresponding to an integrated luminosity of 3 fb(-1), collected by the LHCb experiment at center-of-mass energies of root s = 7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250 < m(chi) < 4700 MeV/c(2) and lifetime 0.1 < tau(chi) < 1000 ps. Upper limits on the branching fraction B(B-broken vertical bar -> K-broken vertical bar chi(mu(vertical bar) mu(-))) at 95% confidence level are set as a function of m(chi) and tau(chi), varying between 2 x 10(-10) and 10(-7). These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). First observation of B+ -> D-s(+) K+ K- decays and a search for B+ -> D-s(+) phi decays. J. High Energy Phys., 01(1), 131–22pp.
Abstract: A search for B+ -> D-s(+) K+ K- decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb(-1), collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be B(B+ -> D-s(+) K+ K-) = (7.1 +/- 0.5 +/- 0.6 +/- 0.7) x 10(-6), where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+ -> D-s(+)(D) over bar (0). A search is also performed for the pure annihilation decay B+ -> D-s(+)(D) over bar (0). No significant signal is observed and a limit of B(B+ -> D-s(+) phi) < 4.9 x 10(-7) (4.2 x 10(-7)) is set on the branching fraction at 95% (90%) confidence level.
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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 B-s(0) -> (KSK)-K-0*(892)(0) at LHCb. J. High Energy Phys., 01(1), 012–17pp.
Abstract: A search for B-(s)(0) -> K-S (0) K*(892)(0) decays is performed using pp collision data, corresponding to an integrated luminosity of 1.0 fb(-1), collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The B-s (0) -> (KSK)-K-0*(892)(0) decay is observed for the first time, with a significance of 7.1 standard deviations. The branching fraction is measured to be B(B-s(0) -> (K) over bar K-0*(892)(0)) + B(B-s(0) -> K-0(K) over bar*(892)(0)) = (16.4 +/- 3.4 +/- 2.3) x10(-6), where the first uncertainty is statistical and the second is systematic. No evidence is found for the decay B-0 ->(KSK)-K-0*(892)(0) and an upper limit is set on the branching fraction, B(B-0 -> (K) over bar K-0*(892)(0)) + B(B-0 -> K-0(K) over bar*(892)(0)) < 0.96 x 10(-6) , at 90 % confidence level. All results are consistent with Standard Model predictions.
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