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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for Heavy Higgs Bosons A/H Decaying to a Top Quark Pair in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 119(19), 191803–20pp.
Abstract: A search for heavy pseudoscalar (A) and scalar (H) Higgs bosons decaying into a top quark pair (t (t) over bar) has been performed with 20.3 fb(-1) of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy root s = 8 TeV. Interference effects between the signal process and standard model t (t) over bar production, which are expected to distort the signal shape from a single peak to a peak-dip structure, are taken into account. No significant deviation from the standard model prediction is observed in the t (t) over bar invariant mass spectrum in final states with an electron or muon, large missing transverse momentum, and at least four jets. The results are interpreted within the context of a type-II two-Higgs-doublet model. Exclusion limits on the signal strength are derived as a function of the mass m(A/H) and the ratio of the vacuum expectation values of the two Higgs fields, tan beta, for m(A/H) > 500 GeV.
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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. (2019). Search for CP Violation in D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) Decays. Phys. Rev. Lett., 122(19), 191803–11pp.
Abstract: A search for charge-parity (CP) violation in Cabibbo-suppressed D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8 fb(-1), collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored D-(s())+ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by CP violation in the neutral kaon system. The results are A(CP)(D-s(+) -> K-S(0)pi(+)) = (1.3 +/- 1.9 +/- 0.5) x 10(-3), A(CP)(D+ -> (KSK+)-K-0) = (-0.09 +/- 0.65 +/- 0.48) x 10(-3), A(CP)(D+ -> phi pi(+)) = (0.05 +/- 0.42 +/- 0.29) x 10(-3), where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with CP symmetry. A combination with previous LHCb measurements, based on data collected at 7 and 8 TeV, is also reported.
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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). Observation of the Decay Lambda(0)(b) -> Lambda(+)(c) tau(-)(nu)over-bar(tau). Phys. Rev. Lett., 128(19), 191803–11pp.
Abstract: The first observation of the semileptonic b-baryon decay Lambda(0)(b) -> Lambda(+)(c) tau(-)(nu) over bar (tau) with a significance of 6.1 sigma, is reported using a data sample corresponding to 3 fb(-1) of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The tau(-) lepton is reconstructed in the hadronic decay to three charged pions. The ratio K = B(Lambda(0)(b) -> Lambda(+)(c) tau(-)(nu) over bar (tau))/B(Lambda(0)(b) -> Lambda(+)(c)pi(-)pi(+)pi(-)) is measured to be 2.46 +/- 0.27 +/- 0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Lambda(0)(b) -> Lambda(+)(c) tau(-)(nu) over bar (tau)) (1.50 +/- 0.16 +/- 0.25 +/- 0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Lambda(0)(b) -> Lambda(+)(c)pi(-)pi(+)pi(-). The ratio of semileptonic branching fractions R(Lambda(+)(c)) B(Lambda(0)(b) -> Lambda(+)(c) tau(-)(nu) over bar (tau))/B(Lambda(0)(b) -> Lambda(+)(c)mu(-)(nu) over bar (tau)) is derived to be 0.242 +/- 0.026 +/- 0.040 +/- 0.059, where the external branching fraction uncertainty from the channel Lambda(0)(b) -> Lambda(+)(c)mu(-)(nu) over bar (tau) contributes to the last term. This result is in agreement with the standard model prediction.
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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). Tests of Lepton Universality Using B-0 -> K(S)(0)l(+) l(-) and B+ -> K*(+)l(+)l(-) Decays. Phys. Rev. Lett., 128(19), 191802–15pp.
Abstract: Tests of lepton universality in B-0 -> K(S)(0)l(+)l(-) and B+ -> K*(+)l(+)l(-) decays where l is either an electron or a muon are presented. The differential branching fractions of B-0 -> K(S)(0)e(+)e(-) and B+ -> K*(+)e(+)e(-) decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The results are consistent with the standard model and previous tests of lepton universality in related decay modes. The first observation of B-0 -> K(S)(0)e(+)e(-) and B+ -> K*(+)e(+)e(-) decays is reported.
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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 B-s(0)-> mu(+) mu(-) Branching Fraction and Effective Lifetime and Search for B-0 ->mu(+) mu(-) Decays. Phys. Rev. Lett., 118(19), 191801–11pp.
Abstract: A search for the rare decays B-s(0)->mu(+)mu(-) and B-0 -> mu(+)mu(-) is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb(-1). An excess of B-s(0) -> mu(+)mu- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B-s(0) -> mu(+)mu(-)) = (3.0 +/- 0.6(-0.2)(+)(0.3)) x 10(-9), where the first uncertainty is statistical and the second systematic. The first measurement of the B-s(0) -> mu(+)mu(-) effective lifetime, tau(B-s(0)-> mu(+) mu(-)) = 2.04 +/- 0.44 +/- 0.05 ps, is reported. No significant excess of B-0 -> mu(+)mu(-) decays is found, and a 95% confidence level upper limit, B(B-0 -> mu(+)mu(-) ) < 3.4 x 10(-10), is determined. All results are in agreement with the standard model expectations.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2018). Search for Resonant and Nonresonant Higgs Boson Pair Production in the b(b)over-bar tau(+) tau(-) Decay Channel in pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 121(19), 191801–24pp.
Abstract: A search for resonant and nonresonant pair production of Higgs bosons in the b (b) over bar tau(+)tau(-) final state is presented. The search uses 36.1 fb(-1) of pp collision data with root s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the tau-lepton pairs with at least one tau lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305 GeV < m(X) < 402 GeV in the simplified hMSSM minimal supersymmetric model for tan beta = 2 and excluding bulk Randall-Sundrum gravitons G(KK) in the mass range 325 GeV < m(GKK) < 885 GeV for k/(M) over bar P-1 = 1.
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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. (2019). Search for Lepton-Universality Violation in B+ -> K(+)l(+)l(-) Decays. Phys. Rev. Lett., 122(19), 191801–13pp.
Abstract: A measurement of the ratio of branching fractions of the decays B+ -> K+mu(+)mu(-) and B+ -> K(+)e(+)e(-) is presented. The proton-proton collision data used correspond to an integrated luminosity of 5.0 fb(-1) recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. For the dilepton mass-squared range 1.1 < q(2) < 6.0 GeV2/c(4) the ratio of branching fractions is measured to be R-K = 0.846(-0.054-0.014)(+0.060+0.016), where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R-K to date and is compatible with the standard model at the level of 2.5 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). Observation of Five New Narrow Omega(0)(c) States Decaying to Xi K-+(c)-. Phys. Rev. Lett., 118(18), 182001–10pp.
Abstract: The Xi K-+(c)- mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3 fb(-1), collected by the LHCb experiment. The Xi(+)(c) is reconstructed in the decay mode pK(-)pi(vertical bar) . Five new, narrow excited Omega(0)(c) states are observed: the Omega(c)(3000)(0), Omega(c)(3050)(0), Omega(c)(3066)(0), Omega(c) (3090)(0), and Omega(c)(3119)(0). Measurements of their masses and widths are reported.
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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). Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector. Phys. Rev. Lett., 131(18), 181901–22pp.
Abstract: This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb(-1) of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688 +/- 23(stat)(-71)(+75) (syst) fb, to be compared with the standard model prediction of 515(-42)(+36) fb at next-to-leading order in QCD.
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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). Search for Baryon-Number Violating Xi(0)(b) Oscillations. Phys. Rev. Lett., 119(18), 181807–9pp.
Abstract: A search for baryon-number violating Xi(0)(b) oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The baryon number at the moment of production is identified by requiring that the Xi(0)(b) come from the decay of a resonance Xi(b)*(-) -> Xi(0)(b)pi(-) or Xi(b)'(-) -> Xi(0)(b)pi(-) and the baryon number at the moment of decay is identified from the final state using the decays Xi(0)(b) -> Xi(0)(c)pi(-) , Xi(+-)(c) -> pK(-)pi(+). No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of omega < 0.08 ps(-1), where. is the associated angular frequency.
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