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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). Search for the Standard Model Higgs boson in the H -> tau(+)tau(-) decay mode in root s=7 TeV pp collisions with ATLAS. J. High Energy Phys., 09(9), 070–50pp.
Abstract: A search for the Standard Model Higgs boson decaying into a pair of tau leptons is reported. The analysis is based on a data sample of proton-proton collisions collected by the ATLAS experiment at the LHC and corresponding to an integrated luminosity of 4.7 fb(-1). No significant excess over the expected background is observed in the Higgs boson mass range of 100-150GeV. The observed (expected) upper limits on the cross section times the branching ratio for H -> tau(+)tau(-) are found to be between 2.9 (3.4) and 11.7 (8.2) times the Standard Model prediction for this mass range.
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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. (2024). Measurement of the Z boson production cross-section in pp collisions at √s=5.02 TeV. J. High Energy Phys., 02(2), 070–38pp.
Abstract: The first measurement of the Z boson production cross-section at centre-of-mass energy v s = 5.02TeV in the forward region is reported, using pp collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 +/- 2 pb-1. The production cross-section is measured for final-state muons in the pseudorapidity range 2.0 <. < 4.5 with transverse momentum pT > 20 GeV/c. The integrated cross-section is determined to be sZ.mu+mu- = 39.6 +/- 0.7(stat) +/- 0.6(syst) +/- 0.8(lumi) pb for the di-muon invariant mass in the range 60 < M μμ< 120 GeV/c2. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in pPb collisions at v sNN = 5.02TeV, the nuclear modification factor RpPb is measured for the first time at this energy. The measured values are 1.2+0.5 -0.3(stat) +/- 0.1(syst) in the forward region (1.53 < y* μ< 4.03) and 3.6+1.6 -0.9(stat)+/- 0.2(syst) in the backward region (-4.97 < y* μ< -2.47), where y* μrepresents the muon rapidity in the centre-of-mass frame.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for same-sign top-quark production and fourth-generation down-type quarks in pp collisions at root s=7 TeV with the ATLAS detector. J. High Energy Phys., 04(4), 069–40pp.
Abstract: A search is preseritecl for same-sign top-quark production and down-type heavy quarks of charge -1/3 in events with two isolated leptons (c or mu) that have the same electric charge, at least two jets and large missing transverse momentum. The data are selected from pp collisions at root s = 7 TeV recorded by the ATLAS detector and correspond to an integrated luminosity of 1.04 fb(-1). The observed data are consistent with expectations from Standard Model processes. Upper limits are set at 95% confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0 pb depending on the assumed mediator mass. Upper limits are also set on the pair-production cross-section for new heavy down-type quarks; a lower limit of 450 GeV is set at 95% confidence level on the mass of heavy down-type quarks under the assumption that they decay 100% of the time to Wt.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of polarization amplitudes and CP asymmetries in B-0 -> phi K*(892)(0). J. High Energy Phys., 05(5), 069–24pp.
Abstract: An angular analysis of the decay B (0) -> phi K (*)(892)(0) is reported based on a pp collision data sample, corresponding to an integrated luminosity of 1.0 fb(-1), collected at a centre-of-mass energy of root S = 7 TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave K+ pi(-) and K+ K- contributions are taken into account and found to be significant. A comparison of the B (0) -> phi K (*)(892)(0) and results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.
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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 the b(b)over-bar decay of the Standard Model Higgs boson in associated (W/Z)H production with the ATLAS detector. J. High Energy Phys., 01(1), 069–89pp.
Abstract: A search for the b (b) over bar decay of the Standard Model Higgs boson is performed with the ATLAS experiment using the full dataset recorded at the LHC in Run 1. The integrated luminosities used are 4.7 and 20.3 fb(-1) from pp collisions at root s = 7 and 8 TeV, respectively. The processes considered are associated (WIZ)H production, where W -> e nu/mu nu, Z -> ee/mu mu, and Z -> nu nu. The observed (expected) deviation from the backgroundonly hypothesis corresponds to a significance of 1.4 (2.6) standard deviations and the ratio of the measured signal yield to the Standard Model expectation is found to be μ= 0.52 +/- 0.32 (stat.) +/- 0.24 (syst.) for a Higgs boson mass of 125.36 GeV. The analysis procedure is validated by a measurement of the yield of (W/Z)Z production with Z -> b (b) over bar in the same final states as for the Higgs boson search, from which the ratio of the observed signal yield to the Standard Model expectation is found to be 0.74 +/- 0.09 (stat.) +/- 0.14 (syst.).
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Aguilera-Verdugo, J. J., Hernandez-Pinto, R. J., Rodrigo, G., Sborlini, G. F. R., & Torres Bobadilla, W. J. (2021). Causal representation of multi-loop Feynman integrands within the loop-tree duality. J. High Energy Phys., 01(1), 69–26pp.
Abstract: The numerical evaluation of multi-loop scattering amplitudes in the Feynman representation usually requires to deal with both physical (causal) and unphysical (non-causal) singularities. The loop-tree duality (LTD) offers a powerful framework to easily characterise and distinguish these two types of singularities, and then simplify analytically the underling expressions. In this paper, we work explicitly on the dual representation of multi-loop Feynman integrals generated from three parent topologies, which we refer to as Maximal, Next-to-Maximal and Next-to-Next-to-Maximal loop topologies. In particular, we aim at expressing these dual contributions, independently of the number of loops and internal configurations, in terms of causal propagators only. Thus, providing very compact and causal integrand representations to all orders. In order to do so, we reconstruct their analytic expressions from numerical evaluation over finite fields. This procedure implicitly cancels out all unphysical singularities. We also interpret the result in terms of entangled causal thresholds. In view of the simple structure of the dual expressions, we integrate them numerically up to four loops in integer space-time dimensions, taking advantage of their smooth behaviour at integrand level.
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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). Search for the radiative Xi(-)(b) -> Xi(-)gamma decay. J. High Energy Phys., 01(1), 069–20pp.
Abstract: The first search for the rare radiative decay Xi(-)(b) -> Xi(-)gamma is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4 fb(-1). The Xi(-)(b) -> Xi(-)-J/ psi channel is used as normalization. No Xi(-)(b) -> Xi(-)gamma signal is found and an upper limit of B(Xi(-)(b) -> Xi(-)gamma) < 1.3 x 10(-4) at 95% confidence level is obtained.
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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). Measurement of Υ production in pp collisions at √s=5 TeV. J. High Energy Phys., 07(7), 069–33pp.
Abstract: The production cross-sections of Υ mesons, namely Υ(1S), Υ(2S) and Υ(3S), in pp collisions at root s = 5TeV are measured with a data sample corresponding to an integrated luminosity of 9.13 +/- 0.18 pb(-1) collected by the LHCb detector. The Υ mesons are reconstructed in the decay mode Υ -> mu(+)mu(-). Double differential cross-sections times branching fractions, as functions of the transverse momentum p(T) and the rapidity y of the Υ mesons, are measured in the range pT < 20 GeV/ c and 2.0 < y < 4.5. The results integrated over these pT and y ranges are sigma((sic)(1S)) x B((sic)(1S) -> mu(+) mu(-)) = 2101 +/- 33 +/- 83 pb, sigma((sic)(2S)) x B((sic)(2S) -> mu(+) mu(-)) = 526 +/- 20 +/- 21 pb, sigma((sic)(3S)) x B((sic)(3S) -> mu(+) mu(-)) = 242 +/- 16 +/- 10 pb, where the first uncertainties are statistical and the second are systematic. The ratios of cross-sections between measurements of two different (sic) states and between measurements at different centre-of-mass energies are determined. The nuclear modification factor of (sic)(1S) at root s = 5TeV is updated as well using the directly measured cross-section results from this analysis.
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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. (2014). Measurement of the production of a W boson in association with a charm quark in pp collisions at root s=7 TeV with the ATLAS detector. J. High Energy Phys., 05(5), 068–67pp.
Abstract: The production of a W boson in association with a single charm quark is studied using 4.6 fb(-1) of pp collision data at root s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96(-0.30)(+0.26) at Q (2) = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W (+) +)/sigma(W (-) + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-(s) over bar quark asymmetry.
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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. (2015). Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at root s=8 TeV. J. High Energy Phys., 01(1), 068–51pp.
Abstract: Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb(-1) from proton-proton collisions at a centre-of-mass energy of root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan,3 between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.
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