ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run-1 data. Eur. Phys. J. C, 76(12), 666–42pp.
Abstract: The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described. Measurements of the photon identification efficiencies are reported, using 4.9 fb(-1) of pp collision data collected at the LHC at root s = 7 TeV and 20.3 fb-1 at root s = 8 TeV. The efficiencies are measured separately for converted and unconverted 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 to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data. Data-to-simulation efficiency ratios used as correction factors in physics measurements are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 10% in 7 TeV data and between 0.5% and 5.6% in 8 TeV data, depending on the photon transverse momentum and pseudorapidity.
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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). Test of CP invariance in vector-boson fusion production of the Higgs boson using the Optimal Observable method in the ditau decay channel with the ATLAS detector. Eur. Phys. J. C, 76(12), 658–25pp.
Abstract: A test of CP invariance in Higgs boson production via vector-boson fusion using the method of the Optimal Observable is presented. The analysis exploits the decay mode of the Higgs boson into a pair of t leptons and is based on 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described in an effective field theory framework, in which the strength of CP violation is governed by a single parameter (d) over tilde. The mean values and distributions of CP-odd observables agree with the expectation in the Standard Model and show no sign of CP violation. The CP-mixing parameter (d) over tilde is constrained to the interval (-0.11, 0.05) at 68% confidence level, consistent with the Standard Model expectation of (d) over tilde = 0.
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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). Luminosity determination in pp collisions at root s=8 TeV using the ATLAS detector at the LHC. Eur. Phys. J. C, 76(12), 653–45pp.
Abstract: The luminosity determination for the ATLAS detector at the LHC during pp collisions at root s = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of delta L/L = +/- 1.9% is obtained for the 22.7 fb(-1) of pp collision data delivered to ATLAS at root s = 8 TeV in 2012.
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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. (2017). Study of WW gamma and WZ gamma production in pp collisions at root s=8 TeV and search for anomalous quartic gauge couplings with the ATLAS experiment. Eur. Phys. J. C, 77(9), 646–30pp.
Abstract: This paper presents a study of WW gamma and WZ gamma triboson production using events from proton-proton collisions at a centre-of-mass energy of root s = 8 TeV recorded with the ATLAS detector at the LHC and corresponding to an integrated luminosity of 20.2 fb(-1). The WW gamma production cross-section is determined using a final state containing an electron, a muon, a photon, and neutrinos (e upsilon μupsilon gamma). Upper limits on the production cross-section of the e upsilon μupsilon gamma final state and theWW gamma and WZ gamma final states containing an electron or a muon, two jets, a photon, and a neutrino (e upsilon j j gamma or μupsilon j j gamma) are also derived. The results are compared to the cross-sections predicted by the Standard Model at next-to-leading order in the strong-coupling constant. In addition, upper limits on the production cross-sections are derived in a fiducial region optimised for a search for newphysics beyond the Standard Model. The results are interpreted in the context of anomalous quartic gauge couplings using an effective field theory. Confidence intervals at 95% confidence level are derived for the 14 coupling coefficients to which WW gamma and WZ gamma production are sensitive.
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