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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Studies of the resonance structure in D-0 -> (KSK +/-)-K-0 pi(-/+) decays. Phys. Rev. D, 93(5), 052018–35pp.
Abstract: Amplitude models are applied to studies of resonance structure in D-0 -> (KSK-)-K-0 pi(+) and D-0 -> (KSK+)-K-0 pi(-) decays using pp collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of 100 MeV/c(2) around the K*(892)(+/-) resonance. Two formulations for the K pi S-wave are used, both of which give a good description of the data. The ratio of branching fractions B(D-0 -> (KSK+)-K-0 pi(-))/B(D-0 -> (KSK-)-K-0 pi(+)) is measured to be 0.655 +/- 0.004(stat) +/- 0.006(syst) over the full phase space and 0.370 +/- 0.003(stat) +/- 0.012(syst) in the restricted region. A search for CP violation is performed using the amplitude models and no significant effect is found. Predictions from SU(3) flavor symmetry for K*(892)K amplitudes of different charges are compared with the amplitude model results.
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BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2011). Studies of tau(-) -> eta K- nu(tau) and tau(-) -> eta pi(-) nu(tau) at BABAR and a search for a second-class current. Phys. Rev. D, 83(3), 032002–10pp.
Abstract: We report on analyses of tau lepton decays tau(-) -> eta K- nu(tau) and tau(-) -> eta pi(-) nu(tau), with eta -> pi(+) pi(-) pi(0), using 470 fb(-1) of data from the BABAR experiment at PEP-II, collected at center-of-mass energies at and near the Y(4S) resonance. We measure the branching fraction for the tau(-) -> eta K- nu(tau) decay mode, B(tau(-) -> eta K- nu(tau)) = (1.42 +/- 0.11(stat) +/- 0.07(syst)) x 10(-4), and report a 95% confidence level upper limit for the second-class current process tau(-) -> eta pi(-) nu(tau), B(tau(-) -> eta pi(-) nu(tau)) < 9.9 x 10(-5).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Strong constraints on the b -> s gamma photon polarisation from B-0 -> K(*0)e(+)e(-) decays. J. High Energy Phys., 12(12), 081–25pp.
Abstract: An angular analysis of the B-0 -> K*(0)e(+)e(-) decay is performed using a data sample corresponding to an integrated luminosity of 9 fb(-1) of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (q(2)) interval between 0.0008 and 0.257 GeV2, where the rate is dominated by the B-0 -> K*(0)gamma transition with a virtual photon. The fraction of longitudinal polarisation of the K*(0) meson, F-L, is measured to be F-L = (4.4 +/- 2.6 +/- 1.4)%, where the first uncertainty is statistical and the second systematic. The A(T)(Re) observable, which is related to the lepton forward-backward asymmetry, is measured to be A(T)(Re) = -0.06 +/- 0.08 +/- 0.02. The A(T)((2)) and A(T)(Im) transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be A(T)((2)) = 0.11 +/- 0.10 +/- 0.02 and A(T)(Im) = 0.02 +/- 0.10 +/- 0.01. The results are consistent with Standard Model predictions and provide the world's best constraint on the b -> s gamma photon polarisation.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2021). Simultaneous determination of CKM angle gamma and charm mixing parameters. J. High Energy Phys., 12(12), 141–32pp.
Abstract: A combination of measurements sensitive to the CP violation angle gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between D-0 and (D) over bar (0) mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN's Large Hadron Collider, are combined for the first time. This method provides an improvement on the precision of the charm mixing parameter y by a factor of two with respect to the current world average. The charm mixing parameters are determined to be x = (0.400(-0.053)(+0.052))% and y = (0.630(-0.030)(+0.033))%. The angle gamma is found to be gamma = (65.4(-4.2)(+3.8))degrees and is the most precise determination from a single experiment.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Searches for violation of lepton flavour and baryon number in tau lepton decays at LHCb. Phys. Lett. B, 724(1-3), 36–45.
Abstract: Searches for the lepton flavour violating decay tau(-) -> mu(-)mu(+)mu(-) and the lepton flavour and baryon number violating decays tau(-) -> (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb(-1), taken by the LHCb experiment at root s = 7 TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: B(tau(-) -> mu(-)mu(+)mu(-) < 8.0 x 10(-8), B(tau(-) -> <(p)over bar>mu(+)mu(-)) < 3.3 x 10(-7) and B(tau(-) -> p mu(-)mu(-)) < 4.4 x 10(-7). The results for the tau(-) -> (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) decay modes represent the first direct experimental limits on these channels.
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