ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). A search for flavour changing neutral currents in top-quark decays in pp collision data collected with the ATLAS detector at root s=7 TeV. J. High Energy Phys., 09(9), 139–37pp.
Abstract: A search for flavour changing neutral current (FCNC) processes in top-quark decays by the ATLAS Collaboration is presented. Data collected from pp collisions at the LHC at a centre-of-mass energy of root s = 7 TeV during 2011, corresponding to an integrated luminosity of 2.1 fb(-1), were used. A search was performed for top-quark pair-production events, with one top quark decaying through the t -> Zq FCNC (q = u, c) channel, and the other through the Standard Model dominant mode t -> Wb. Only the decays of the Z boson to charged leptons and leptonic W-boson decays were considered as signal. Consequently, the final-state topology is characterised by the presence of three isolated charged leptons, at least two jets and missing transverse momentum from the undetected neutrino. No evidence for an FCNC signal was found. An upper limit on the t -> Zq branching ratio of BR(t -> Zq) < 0.73% is set at the 95% confidence level.
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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 asymmetries in the decays B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-). J. High Energy Phys., 09(9), 177–18pp.
Abstract: The direct CP asymmetries of the decays B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-) are measured using pp collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected with the LHCb detector. The respective control modes B-0 -> J/psi K+ and B+ -> J/psi K+ are used to account for detection and production asymmetries. The measurements are made in several intervals of mu(+)mu(-) invariant mass squared, with the phi(1020) and charmonium resonance regions excluded. Under the hypothesis of zero CP asymmetry in the control modes, the average values of the asymmetries are A(CP)(B-0 -> K-*0 mu(+) mu(-) and B+ -> K+ mu(+) mu(-)) = -0.035 +/- 0.024 +/- 0.003, A(CP)(B+ -> K+ mu(+) mu(-) = 0.012 +/- 0.017 +/- 0.001, where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small CP asymmetry in these decays.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Differential branching fraction and angular analysis of the decay B-0 -> K*(0)mu(+)mu(-). J. High Energy Phys., 08(8), 131–31pp.
Abstract: The angular distribution and differential branching fraction of the decay B-0 -> K*(0)mu(+)mu(-) are studied using a data sample, collected by the LHCb experiment in pp collisions at root s = 7 TeV, corresponding to an integrated luminosity of 1.0 fb(-1). Several angular observables are measured in bins of the dimuon invariant mass squared, q(2). A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q(0)(2) = 4.9 +/- 0.9 GeV2/c(4), where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of CP asymmetries and polarisation fractions in B-s(0) -> K*(0)(K)over-bar*(0) decays. J. High Energy Phys., 07(7), 166–28pp.
Abstract: An angular analysis of the decay B-s(0) -> K*(0)(K) over bar*(0) is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb(-1) collected by the LHCb experiment at a centre-of-mass energy root s = 7TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f(L) = 0.201 +/- 0.057 (stat.) +/- 0.040 (syst.) for the B-s(0) -> K*(892)(0)(K) over bar*(892)(0) decay. A large scalar contribution from the K*(0) (1430) and K*(0) (800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(B-s(0) -> K*(892)(0)(K) over bar*(892)(0)) is measured to be (10.8 +/- 2.1 (stat.) +/- 1.4 (syst.) +/- 0.6 (f(d)/f(s))) x 10(-6).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Differential branching fractions and isospin asymmetries of B -> K ((*)) μ(+) μ(-) decays. J. High Energy Phys., 06(6), 133–22pp.
Abstract: The isospin asymmetries of B -> K μ(+) μ(-) and B -> K (*) μ(+) μ(-) decays and the partial branching fractions of the B (0) -> K (0) μ(+) μ(-), B (+) -> K (+) μ(+) μ(-) and B (+) -> K (*+) μ(+) μ(-) decays are measured as functions of the dimuon mass squared, q (2). The data used correspond to an integrated luminosity of 3 fb(-1) from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.
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