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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). Measurement of the azimuthal ordering of charged hadrons with the ATLAS detector. Phys. Rev. D, 86(5), 052005–25pp.
Abstract: This paper presents a study of the possible ordering of charged hadrons in the azimuthal angle relative to the beam axis in high-energy proton-proton collisions at the Large Hadron Collider (LHC). A spectral analysis of correlations between longitudinal and transverse components of the momentum of the charged hadrons, driven by the search for phenomena related to the structure of the QCD field, is performed. Data were recorded with the ATLAS detector at center-of-mass energies of root s = 900 GeV and root s = 7 TeV. The correlations measured in a kinematic region dominated by low-p(T) particles are not well described by conventional models of hadron production. The measured spectra show features consistent with the fragmentation of a QCD string represented by a helixlike ordered gluon chain.
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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. (2014). Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at root s=7 TeV in 2010. Eur. Phys. J. C, 74(9), 3034–32pp.
Abstract: This paper presents a study of the performance of the muon reconstruction in the analysis of proton-proton collisions at root s = 7TeV at the LHC, recorded by the ATLAS detector in 2010. This performance is described in terms of reconstruction and isolation efficiencies and momentum resolutions for different classes of reconstructed muons. The results are obtained from an analysis of J/psi meson and Z boson decays to dimuons, reconstructed from a data sample corresponding to an integrated luminosity of 40 pb(-1). The measured performance is compared to Monte Carlo predictions and deviations from the predicted performance are discussed.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2012). Search for lepton flavour violation in the e-mu continuum with the ATLAS detector in root s=7 TeV pp collisions at the LHC. Eur. Phys. J. C, 72(6), 2040–19pp.
Abstract: This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ((t) over tilde) in the e(+/-)mu(-/+) continuum using 2.1 fb(-1) of data collected by the ATLAS detector in root s = 7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass (m((t) over tilde)). The upper limits on the production cross section for pp -> e μX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m((t) over tilde) = 95 GeV to 30 fb for m((t) over tilde) = 1000 GeV.
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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). Search for new particles in events with one lepton and missing transverse momentum in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 037–43pp.
Abstract: This paper presents a search for new particles in events with one lepton (electron or muon) and missing transverse momentum using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded by the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 3.24 TeV. Excited chiral bosons (W*) with equivalent coupling strengths are excluded for masses up to 3.21 TeV. In the framework of an effective field theory limits are also set on the dark matter-nucleon scattering cross-section as well as the mass scale M-* of the unknown mediating interaction for dark matter pair production in association with a leptonically decaying W.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at root s=8 TeV with the ATLAS detector at the LHC. Phys. Rev. D, 92(9), 092001–30pp.
Abstract: This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Z(d), H -> ZZ(d) -> 4l or H -> Z(d)Z(d) -> 4l. The search was performed using pp collision data corresponding to an integrated luminosity of about 20 fb(-1) at the center-of-mass energy of root s = 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H -> ZZ(d) -> 4l and on the kinetic mixing parameter between the Z(d) and the Standard Model hypercharge gauge boson are set in the range (1-9) x 10(-5) and (4-17) x 10(-2) respectively, at 95% confidence level assuming the Standard Model branching ratio of H -> ZZ* -> 4l, for Z(d) masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Z(d) are also set using the branching ratio limits in the H -> ZZ(d) -> 4l search, and are in the range (1.5-8.7) x 10(-4) for 15 < m(Zd) < 35 GeV. Upper bounds on the branching ratio of H -> Z(d)Z(d) -> 4l and on the Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons are set in the range (2-3) x 10(-5) and (1-10) x 10(-4) respectively, at 95% confidence level assuming the Standard Model Higgs boson production cross sections, for Z(d) masses between 15 and 60 GeV.
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