ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., et al. (2018). Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector. Eur. Phys. J. C, 78(8), 625–38pp.
Abstract: A search for new phenomena in final states containing an e(+)e(-) or m(+)m(-) pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton-proton collision data with an integrated luminosity of 36.1 fb(-1), collected during 2015 and 2016 at a centre of-mass energy Os = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an e(+)e(-) or m(+)m(-) pair and the lightest neutralino ((c) over tilde (0)(1)) via one of two next-to-lightest neutralino ((c) over tilde (0)(2)) decay mechanisms: (c) over tilde (0)(2) Z (c) over tilde (0)(1), where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and (c) over tilde (0)(2) l(+)1(-) (c) over tilde (0)(1) with no intermediate l(+)l(-) resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 TeV at 95% confidence level, 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. (2018). Measurement of tau polarisation in Z/gamma* -> tau tau decays in proton-proton collisions at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 78(2), 163–30pp.
Abstract: This paper presents a measurement of the polarisation of tau leptons produced in Z/gamma* -> tau tau decays which is performed with a dataset of proton-proton collisions at root s = 8 TeV, corresponding to an integrated luminosity of 20.2 fb(-1) recorded with the ATLAS detector at the LHC in 2012. The Z/gamma* -> tau tau decays are reconstructed from a hadronically decaying tau lepton with a single charged particle in the final state, accompanied by a tau lepton that decays leptonically. The tau polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic tau decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The tau polarisation extracted over the full phase space within the Z/gamma* mass range of 66 < mZ/gamma* < 116GeVis found to be P-tau = -0.14 +/- 0.02(stat)+/- 0.04(syst). It is in agreement with the Standard Model prediction of Pt = -0.1517 +/- 0.0019, which is obtained from the ALP-GEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA tau decay library.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo, F. L., et al. (2018). Search for Higgs boson pair production in the..WW * channel using pp collision data recorded at v s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 78(12), 1007–26pp.
Abstract: Searches for non- resonant and resonant Higgs boson pair production are performed in the..WW * channel with the final state of.. .j j using 36.1 fb – 1 of protonpv roton collision data recorded at a centre- of- mass energy of s = 13 TeV by the ATLAS detector at the Large Hadron Collider. No significant deviation from the Standard Model prediction is observed. A 95% confidence- level observed upper limit of 7.7 pb is set on the cross section for nonresonant production, while the expected limit is 5.4 pb. A search for a narrow- width resonance X decaying to a pair of Standard Model Higgs bosons HH is performed with the same set of data, and the observed upper limits on s( pp. X) x B( X. HH) range between 40.0 and 6.1 pb for masses of the resonance between 260 and 500GeV, while the expected limits range between 17.6 and 4.4 pb. When deriving the limits above, the StandardModel branching ratios of the H... and H. WW * are assumed.
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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). Measurements of W and Z boson production in pp collisions at root s=5.02 TeV with the ATLAS detector. Eur. Phys. J. C, 79(2), 128–29pp.
Abstract: Measurements of fiducial integrated and differential cross sections for inclusive W +, W -and Z boson production are reported. They are based on 25.0 +/- 0.5 pb -1 of pp collision data at v s = 5.02 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined W +, W -and Z integrated cross sections are found to be sW+ = 2266 +/- 9 (stat) +/- 29 (syst) +/- 43 (lumi) pb, sW-= 1401 +/- 7 (stat) +/- 18 (syst) +/- 27 (lumi) pb, and sZ = 374.5 +/- 3.4 (stat)+/- 3.6 (syst)+/- 7.0 (lumi) pb, in good agreement with next-to-next-to-leading-order QCD crosssection calculations. Thesemeasurements serve as references for Pb+ Pb interactions at the LHC at v sNN = 5.02 TeV.
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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 the photon identification efficiencies with the ATLAS detector using LHC Run 2 data collected in 2015 and 2016. Eur. Phys. J. C, 79(3), 205–41pp.
Abstract: The efficiency of the photon identification criteria in the ATLAS detector is measured using 36.1 fb1 to 36.7 fb1 of pp collision data at v s = 13 TeV collected in 2015 and 2016. The efficiencies are measured separately for converted and unconverted isolated photons, in four different pseudorapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared with the predictions from simulation after correcting the variables describing the shape of electromagnetic showers in simulation for the average differences observed relative to data. Data-tosimulation efficiency ratios are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 5% depending on the photon transverse momentum and pseudorapidity. The impact of the isolation criteria on the photon identification efficiency, and that of additional soft pp interactions, are also discussed. The probability of reconstructing an electron as a photon candidate ismeasured in data, and compared with the predictions from simulation. The efficiency of the reconstruction of photon conversions is measured using a sample of photon candidates from Z. μmu. events, exploiting the properties of the ratio of the energies deposited in the first and second longitudinal layers of the ATLAS electromagnetic calorimeter.
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