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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). A measurement of the CP asymmetry difference between Lambda(+)(C) -> pK(-)K(+) and p pi(-)pi(+) decays. J. High Energy Phys., 03(3), 182–21pp.
Abstract: The difference between the CP asymmetries in the decays Lambda(+)(C) -> pK(-)K(+) and Lambda(+)(C) -> p pi(-)pi(+) is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb(-1). The Lambda(+)(C) candidates are reconstructed as part of the Lambda(0)(b) -> Lambda(+)(c)mu X- decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Lambda(+)(C) -> pK(-)K(+) sample. This alters the definition of the integrated CP asymmetry to A(CP)(wgt)(p pi(-)pi(+)). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Lambda(+)(C) decay phase space. The difference in CP asymmetries is found to be Delta A(CP)(wgt) = A(CP)(pK(-)K(+)) – A(CP)(wgt)(p pi(-)pi(+)) = (0.30 +/- 0.91 +/- 0.61) %, where the first uncertainty is statistical and the second is systematic.
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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). A precise measurement of the B-0 meson oscillation frequency. Eur. Phys. J. C, 76(7), 412–14pp.
Abstract: The oscillation frequency, Delta m(d), of B-0 mesons is measured using semileptonic decays with a D- or D*(-) meson in the final state. The data sample corresponds to 3.0 fb(-1) of pp collisions, collected by the LHCb experiment at centre-of-mass energies root s = 7 and 8 TeV. A combination of the two decay modes gives Delta m(d) = (505.0 +/- 2.1 +/- 1.0) ns(-1), where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., & Ruiz Valls, P. (2014). A study of CP violation in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays with D -> (KSK +/-)-K-0 pi(-/+) final states. Phys. Lett. B, 733, 36–45.
Abstract: 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.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2017). Amplitude analysis of B+ -> J/psi phi K+ decays. Phys. Rev. D, 95(1), 012002–28pp.
Abstract: The first full amplitude analysis of B+ -> J/psi phi K+ with J/psi -> mu(+)mu(-), phi -> K+K- decays is performed with a data sample of 3 fb(-1) of pp collision data collected at root s = 7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into phi K+, and four J/psi phi structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state. The model includes significant contributions from a number of expected kaon excitations, including the first observation of the K*(1680)+ -> phi K+ transition.
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