ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Top-quark mass measurement in the all-hadronic t(t)over-bar decay channel at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 118–41pp.
Abstract: The top-quark mass is measured in the all-hadronic top-antitop quark decay channel using proton-proton collisions at a centre-of-mass energy of root s = 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The data set used in the analysis corresponds to an integrated luminosity of 20.2 fb(-1). The large multi-jet background is modelled using a data-driven method. The top-quark mass is obtained from template fits to the ratio of the three-jet to the dijet mass. The three-jet mass is obtained from the three jets assigned to the top quark decay. From these three jets the dijet mass is obtained using the two jets assigned to the W boson decay. The top-quark mass is measured to be 173.72 +/- 0.55 (stat.) +/- 1.01 (syst.) GeV.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the time-integrated CP asymmetry in D-0 -> (KSKS0)-K-0 decays. J. High Energy Phys., 10(10), 055–15pp.
Abstract: The time-integrated CP asymmetry in the decay D-0 -> (KSKS0)-K-0 is measured using 3 fb(-1) of proton-proton collision data collected by the LHCb experiment at centreof- mass energies of 7 and 8TeV. The flavour of the D-0 meson is determined by use of the decay D*(+) -> D-0 pi(+) and its charge conjugate mode. The result is A(CP) = -0.029 +/- 0.052 +/- 0.022, where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of CP violation in two-body B-(s)(0)-meson decays to charged pions and kaons. J. High Energy Phys., 03(3), 075–43pp.
Abstract: The time-dependent CP asymmetries of B-0 -> pi(+)pi(-) and B-s(0) -> K+K- decays are measured using a data sample of pp collisions corresponding to an integrated luminosity of 1.9 fb(-1), collected with the LHCb detector at a centre-of-mass energy of 13TeV. The results are C-pi pi = 0.311 +/- 0.045 +/- 0.015; S-pi pi = 0.706 +/- 0.042 +/- 0.013; C-KK = 0.164 +/- 0.034 +/- 0.014; S-KK = 0.123 +/- 0.034 +/- 0.015; A(KK)(Delta Gamma) = -0.83 +/- 0.05 +/- 0.09; where the first uncertainties are statistical and the second systematic. The same data sample is used to measure the time-integrated CP asymmetries of B-0 -> K + pi(-) and B-s(0) -> K-pi(+) decays and the results are AB(CP)(B0) = -0.0824 +/- 0.0033 +/- 0.0033; A(CP)(Bs0) = 0.236 +/- 0.013 +/- 0.011. All results are consistent with earlier measurements. A combination of LHCb measurements provides the first observation of time-dependent CP violation in B-s(0) decays.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2015). Measurement of the t(t)over-bar production cross-section as a function of jet multiplicity and jet transverse momentum in 7 TeV proton-proton collisions with the ATLAS detector. J. High Energy Phys., 01(1), 020–67pp.
Abstract: The t (t) over bar production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb(-1). Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all known detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Observation of the suppressed decay Lambda(0)(b) -> p pi(-) mu(+) mu(-). J. High Energy Phys., 04(4), 029–16pp.
Abstract: The suppressed decay Lambda(0)(b) -> p pi(-) mu(+) mu(-), excluding the J/psi and psi(2S) -> mu(+) mu(-) resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton- proton collision data corresponding to an integrated luminosity of 3 fb(-1) collected with the LHCb experiment. The Lambda(0)(b) -> p pi(-) mu(+) mu(-) branching fraction is measured relative to the Lambda(0)(b) -> J/psi (-> mu(+) mu(-)) p pi(-) branching fraction giving B (Lambda(0)(b) -> p pi(-) mu(+) mu(-))/B(Lambda(0)(b) -> J/psi (-> mu(+) mu(-)) p pi(-)) = 0.044 +/- 0.012 +/- 0.007, where the first uncertainty is statistical and the second is systematic. This is the first observation of a b -> d transition in a baryonic decay.
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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). Measurement of the shape of the B-s(0) -> D-s*(-) mu(+) nu(mu) differential decay rate. J. High Energy Phys., 12(12), 144–32pp.
Abstract: The shape of the B-s(0) -> D-s*mu(+)nu(mu) differential decay rate is obtained as a function of the hadron recoil parameter using proton-proton collision data at a centreof-mass energy of 13TeV, corresponding to an integrated luminosity of 1.7 fb(-1) collected by the LHCb detector. The B-s(0) -> D-s*(-)mu(+)nu(mu) decay is reconstructed through the decays D-s*(-) up arrow D-s(-) gamma and D-s(-) -> K-K+pi(-). The differential decay rate is fitted with the CapriniLellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.
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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 pair production of vector-like top quarks in events with one lepton, jets, and missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 08(8), 052–40pp.
Abstract: The results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for pair production of vector-like top quarks in the Z(->nu nu) t + X decay channel. LHC pp collision data at a centre-of-mass energy of root S = 13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb(-1). No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like T quark pair as a function of the T quark mass are derived. The observed (expected) 95% CL lower limits on the T mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure Zt decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.
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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. (2014). Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in root s=8 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 11(11), 118–87pp.
Abstract: The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton-proton collision data at root s = 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb(-1). The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a W boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the W bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model.
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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. (2018). Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb(-1) of root s=13 TeV pp collision data with the ATLAS detector. J. High Energy Phys., 06(6), 108–96pp.
Abstract: The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of root s = 13TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb(-1). A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. Stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 04(4), 116–75pp.
Abstract: The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy root s = 8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb(-1). No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R-c = 950 GeV for a cut-off scale times radius (Lambda R-c) of approximately 30.
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