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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. (2016). Search for high-mass new phenomena in the dilepton final state using proton-proton collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 761, 372–392.
Abstract: A search is conducted for both resonant and non-resonant high-mass new phenomena in dielectron and dimuon final states. The search uses 3.2 fb(-1) of proton-proton collision data, collected at root s = 13 TeV by the ATLAS experiment at the LHC in 2015. The dilepton invariant mass is used as the discriminating variable. No significant deviation from the Standard Model prediction is observed; therefore limits are set on the signal model parameters of interest at 95% credibility level. Upper limits are set on the cross-section times branching ratio for resonances decaying to dileptons, and the limits are converted into lower limits on the resonance mass, ranging between 2.74 TeV and 3.36 TeV, depending on the model. Lower limits on the llqq contact interaction scale are set between 16.7 TeV and 25.2 TeV, also depending on the 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. (2016). Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at root s=13 TeV. Phys. Lett. B, 760, 520–537.
Abstract: A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb (1) of proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at root s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
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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. (2016). Search for heavy long-lived charged R-hadrons with the ATLAS detector in 3.2 fb(-1) of proton-proton collision data at root s=13 TeV. Phys. Lett. B, 760, 647–665.
Abstract: A search for heavy long-lived charged R-hadronsis reported using a data sample corresponding to 3.2fb(-1)of proton-proton collisions at root s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider at CERN. The search is based on observables related to large ionisation losses and slow propagation velocities, which are signatures of heavy charged particles travelling significantly slower than the speed of light. No significant deviations from the expected background are observed. Upper limits at 95% confidence level are provided on the production cross section of long-lived R-hadronsin the mass range from 600 GeV to 2000 GeV and gluino, bottom and top squark masses are excluded up to 1580 GeV, 805 GeV and 890 GeV, respectively.
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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. (2016). Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at root S=13 TeV with the ATLAS detector. Phys. Lett. B, 759, 229–246.
Abstract: Searches for high-mass resonances in the dijet invariant mass spectrum with one or two jets identified as b-jets are performed using an integrated luminosity of 3.2 fb(-1) of proton-proton collisions with a centre-of-mass energy of root S = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% credibility level, excited b* quarks with masses from 1.1 TeV to 2.1 TeV and leptophobic Z' bosons with masses from 1.1 TeV to 1.5 TeV. Contributions of a Gaussian signal shape with effective cross sections ranging from approximately 0.4 to 0.001 pb are also excluded in the mass range 1.5-5.0 TeV.
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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. (2016). Search for charged Higgs bosons produced in association with a top quark and decaying via H-+/- -> tau nu using pp collision data recorded at root s=13 TeV by the ATLAS detector. Phys. Lett. B, 759, 555–574.
Abstract: Charged Higgs bosons produced in association with a single top quark and decaying via H-+/- -> tau nu are searched for with the ATLAS experiment at the LHC, using proton-proton collision data at root s = 13 TeV corresponding to an integrated luminosity of 3.2 fb(-1). The final state is characterised by the presence of a hadronic tau decay and missing transverse momentum, as well as a hadronically decaying top quark, resulting in the absence of high-transverse-momentum electrons and muons. The data are found to be consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the production cross section times branching fraction, sigma (pp -> [b]tH(+/-)) x BR(H-+/- -> tau nu), between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV. The exclusion limits for this search surpass those obtained with the proton-proton collision data recorded at root s = 8 TeV.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurement of W-+/- and Z-boson production cross sections in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 759, 601–621.
Abstract: Measurements of the W-+/- -> l(+/-) v and Z -> l(+)l(-) production cross sections (where l(+/-) = e(+/-), mu(+/-)) in proton-proton collisions at root s = 13 TeV are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb(-1). The total inclusive W+-boson production cross sections times the single-lepton-flavour branching ratios are sigma(tot)(w+) = 11.83 +/- 0.02 (stat) +/- 0.32 (sys) +/- 0.25 (lumi) nb and sigma(tot)(W-) = 8.79 +/- 0.02 (stat) +/- 0.24 (sys) +/- 0.18 (lumi) nb for W+ and W-, respectively. The total inclusive Z-boson production cross section times leptonic branching ratio, within the invariant mass window 66 < m(tt) < 116 GeV, is sigma(tot)(Z) = 1.981 +/- 0.007 (stat) +/- 0.038 (sys) +/- 0.042 (lumi) nb. The W+, W-, and Z-boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The cross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in sigma(fid)(W+)/sigma(fid)(W-) = 1.295 +/- 0.003 (stat) +/- 0.010 (sys) and sigma(fid)(W +/-)/sigma(fid)(Z) = 10.31 +/- 0.04 (stat) +/- 0.20 (sys). Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and to next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., et al. (2022). Observation of WWW Production in pp Collisions at p=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 129(6), 061803–20pp.
Abstract: This Letter reports the observation of WWW production and a measurement of its cross section using detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWW production cross section is measured to be 820 ± 100 (stat) ± 80 (syst) fb, approximately 2.6 standard deviations from the predicted cross section of 511 ± 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for Displaced Leptons in root s=13 TeV pp Collisions with the ATLAS Detector. Phys. Rev. Lett., 127(5), 051802–21pp.
Abstract: A search for charged leptons with large impact parameters using 139 fb(-1) of root s = 13 TeV pp collision data from the ATLAS detector at the LHC is presented, addressing a long-standing gap in coverage of possible new physics signatures. Results are consistent with the background prediction. This search provides unique sensitivity to long-lived scalar supersymmetric lepton partners (sleptons). For lifetimes of 0.1 ns, selectron, smuon, and stau masses up to 720, 680, and 340 GeV, respectively, are excluded at 95% confidence level, drastically improving on the previous best limits from LEP.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for New Phenomena in Final States with Two Leptons and One or No b-Tagged Jets at root s=13 TeV Using the ATLAS Detector. Phys. Rev. Lett., 127(14), 141801–23pp.
Abstract: A search for new phenomena is presented in final states with two leptons and one or no b-tagged jets. The event selection requires the two leptons to have opposite charge, the same flavor (electrons or muons), and a large invariant mass. The analysis is based on the full run-2 proton-proton collision dataset recorded at a center-of-mass energy off root S = 13 TeV by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 139 fb(-1). No significant deviation from the expected background is observed in the data. Inspired by the B-meson decay anomalies, a four-fermion contact interaction between two quarks (b, s) and two leptons (ee or μmu) is used as a benchmark signal model, which is characterized by the energy scale and coupling, Lambda and g(*), respectively. Contact interactions with Lambda/g(*) lower than 2.0 (2.4) TeV are excluded for electrons (muons) at the 95% confidence level, still far below the value that is favored by the B-meson decay anomalies. Model-independent limits are set as a function of the minimum dilepton invariant mass, which allow the results to be reinterpreted in various signal scenarios.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo Gimenez, V., et al. (2021). Search for Lepton-Flavor Violation in Z-Boson Decays with tau Leptons with the ATLAS Detector. Phys. Rev. Lett., 127(27), 271801–20pp.
Abstract: A search for lepton-flavor-violating Z -> e tau and Z -> μtau decays with pp collision data recorded by the ATLAS detector at the LHC is presented. This analysis uses 139 fb(-1) of Run 2 pp collisions at root s = 13 TeV and is combined with the results of a similar ATLAS search in the final state in which the tau lepton decays hadronically, using the same data set as well as Run 1 data. The addition of leptonically decaying tau leptons significantly improves the sensitivity reach for Z -> l tau decays. The Z -> l tau branching fractions are constrained in this analysis to B(Z -> e tau) < 7.0 x 10(-6) and B (Z -> μtau) < 7.2 x 10(-6) at 95% confidence level. The combination with the previously published analyses sets the strongest constraints to date: B(Z -> e tau) < 5.0 x 10(-6) and B(Z -> μtau) < 6.5 x 10(-6) at 95% confidence level.
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