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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). Searches for exclusive Higgs and Z boson decays into J/psi gamma, psi (2S) gamma, and Upsilon(nS) gamma at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 786, 134–155.
Abstract: Searches for the exclusive decays of the Higgs and Z bosons into a J/psi, psi(2S), or Upsilon(nS) (n = 1, 2, 3) meson and a photon are performed with a pp collision data sample corresponding to an integrated luminosity of 36.1 fb(-1) collected at root s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence- level upper limits on the branching fractions of the Higgs boson decays to J/psi gamma, psi(2S) gamma and Upsilon(nS) gamma of 3.5 x 10(-4), 2.0 x 10(-3), and (4.9, 5.9, 5.7) x 10(-4), respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the Z boson decays are 2.3 x 10(-6), 4.5 x 10(-6) and (2.8, 1.7, 4.8) 10(-6), respectively.
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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). Measurement of the t(t)over-bar production cross-section in pp collisions at root s=5.02 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 138–54pp.
Abstract: The inclusive top-quark pair ( t (t) over bar) production cross-section sigma(t (t) over bar) is measured in proton-proton collisions at a centre-of-mass energy root s = 5.02TeV, using 257 pb(-1) of data collected in 2017 by the ATLAS experiment at the LHC. The t (t) over bar cross-section is measured in both the dilepton and single-lepton final states of the t<overline> t system and then combined. The combination of the two measurements yields sigma(t (t) over bar) = 67.5 +/- 0.9 (stat.) +/- 2.3 (syst.) +/- 1.1 (lumi.) +/- 0.2 (beam) pb, where the four uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, and imperfect knowledge of both the integrated luminosity and the LHC beam energy, giving a total uncertainty of 3.9%. The result is in agreement with theoretical quantum chromodynamic calculations at next-to-next-to-leading order in the strong coupling constant, including the resummation of next-to-next-to-leading logarithmic soft-gluon terms, and constrains the parton distribution functions of the proton at large Bjorken-x.
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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 charged Higgs bosons decaying via H-+/- -> tau(+/-)nu(tau) in the tau plus jets and tau plus lepton final states with 36 fb(-1) of pp collision data recorded at root s=13 TeV with the ATLAS experiment. J. High Energy Phys., 09(9), 139–48pp.
Abstract: Charged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via H-+/-! -> tau(+/-)nu(tau), are searched for in 36.1 fb(-1) of proton-proton collision data at root s = 13TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with H-+/- decays hadronically or leptonically, the search targets tau+jets and tau+lepton fi nal states, in both cases with a hadronically decaying tau-lepton. No evidence of a charged Higgs boson is found. For the mass range of m(H)+/- = 90-2000 GeV, upper limits at the 95% con fi dence level are set on the production cross-section of the charged Higgs boson times the branching fraction B (H-+/-->tau(+/-)nu(tau)) in the range 4.2-0.0025 pb. In the mass range 90{160 GeV, assuming the Standard Model cross-section for tit production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction B (t -> bH(+/-)) x B (H-+/- -> tau(+/-)nu(tau)).
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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. (2019). Measurement of VH, H -> b(b)over-barproduction as a function of the vector-boson transverse momentum in 13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 05(5), 141–36pp.
Abstract: Cross-sections of associated production of a Higgs boson decaying into bottomquark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the simplified template cross-section' framework. The results are obtained using 79.8 fb(-1) of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Inclusive and differential cross-sections for dilepton ttbar production measured in √s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 07(7), 141–78pp.
Abstract: Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (t (t) over bar) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of root s = 13TeV and correspond to an integrated luminosity of 140 fb(-1). The measurements use events containing an oppositely charged e μpair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p(T) distributions is obtained by reweighting the t (t) over bar sample so as to reproduce the top-quark p(T) distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be sigma(t (t) over bar) = 829 +/- 1 (stat) +/- 13 (syst) +/- 8 (lumi) +/- 2 (beam) pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
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