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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 measurement of the CP-violating phase phi(dd)(s) in B-s(0) -> (K+pi(-))(K-pi(+)) decays. J. High Energy Phys., 03(3), 140–32pp.
Abstract: A flavour-tagged decay-time-dependent amplitude analysis of B-s(0) -> (K+pi(-))(K-pi(+)) decays is presented in the K-+/-pi(-/+) mass range from 750 to 1600 MeV/c(2). The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb(-1). Several quasi-two-body decay modes are considered, corresponding to K-+/-pi(-/+) combinations with spin 0, 1 and 2, which are dominated by the K-0(*)(800)(0) and K-0(*)(1430)(0), the K*(892)(0) and the K-2(*)(1430)(0) resonances, respectively. The longitudinal polarisation fraction for the B-s(0) -> K-*(892)(0) (K*) over bar (892)(0) decay is measured as f(L) = 0.208 +/- 0.032 +/- 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CP-violating phase in phi(d (d) over bar)(s), in b -> d (s) over bars transitions is performed, yielding a value of phi(d (d) over bar)(s)= -0.10 +/- 0.13 (stat) +/- 0.14 (syst) rad.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Measurement of the lifetimes of promptly produced Omega(0)(c) and Xi(9)(c) baryons. Sci. Bull., 67(5), 479–487.
Abstract: A measurement of the lifetimes of the Omega(0)(c) and Xi(0)(c) baryons is reported using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1) collected by the LHCb experiment. The Omega(0)(c) and Xi(0)(c) baryons are produced directly from proton interactions and reconstructed in the pK(-)K(-)pi(+) final state. The Omega(0)(c) lifetime is measured to be 276.5 +/- 13.4 +/- 4.4 +/- 0.7 fs, and the Xi(0)(c) lifetime is measured to be 148.0 +/- 2.3 +/- 2.2 +/- 0.2 fs, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the D-0 lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter Omega(c)0 lifetime, and provide the single most precise measurement of the Omega(0 )(c)lifetime.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Search for CP violation in D(s)+ → K- K+ K+ decays. J. High Energy Phys., 07(7), 067–25pp.
Abstract: A search for direct CP violation in the Cabibbo-suppressed decay D-s(+) -> K-K+ K+ and in the doubly Cabibbo-suppressed decay D+ -> K- K+ K+ is reported. The analysis is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13TeV corresponding to an integrated luminosity of 5.6 fb(-1). The search is conducted by comparing the D-(s)(+) and D-(s)(-) Dalitz-plot distributions through a model-independent binned technique, based on fits to the K-K+K+ invariantmass distributions, with a total of 0.97 (1.27) million D-s(+) (D+) signal candidates. The results are given as p-values for the hypothesis of CP conservation and are found to be 13.3% for the D+ -> K-K+ K+ decay and 31.6% for the D+ -> K-K+ K+ decay. No evidence for CP violation is observed in these decays.
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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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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Search for flavour-changing neutral current interactions of the top quark and the Higgs boson in events with a pair of tau-leptons in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 155–57pp.
Abstract: A search for flavour-changing neutral current (FCNC) tqH interactions involving a top quark, another up-type quark (q = u, c), and a Standard Model (SM) Higgs boson decaying into a tau-lepton pair (H -> tau(+)tau(-)) is presented. The search is based on a dataset of pp collisions at root s = 13 TeV that corresponds to an integrated luminosity of 139 fb(-1) recorded with the ATLAS detector at the Large Hadron Collider. Two processes are considered: single top quark FCNC production in association with a Higgs boson (pp -> tH), and top quark pair production in which one of top quarks decays into Wb and the other decays into qH through the FCNC interactions. The search selects events with two hadronically decaying tau-lepton candidates (tau(had)) or at least one tau(had) with an additional lepton (e, mu), as well as multiple jets. Event kinematics is used to separate signal from the background through a multivariate discriminant. A slight excess of data is observed with a significance of 2.3 sigma above the expected SM background, and 95% CL upper limits on the t -> qH branching ratios are derived. The observed (expected) 95% CL upper limits set on the t -> cH and t -> uH branching ratios are 9.4x10(-4)(4.8(-1.4)(+2.2) x 10(-4)) and 6.9x10(-4) (3.5(-1.0)(+1.5) x10(-4)), respectively. The corresponding combined observed (expected) upper limits on the dimension-6 operator Wilson coefficients in the effective tqH couplings are C-c phi < 1.35 (0.97) and C-u phi < 1.16 (0.82).
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