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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. (2013). Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector. Nucl. Phys. B, 875(3), 483–535.
Abstract: The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb(-1). Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon jet invariant mass and the scattering angle in the photon jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle.
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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. (2013). Measurement of the high-mass Drell-Yan differential cross-section in pp collisions at root s=7 TeV with the ATLAS detector. Phys. Lett. B, 725(4-5), 223–242.
Abstract: This Letter reports a measurement of the high-mass Drell-Yan differential cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. Based on an integrated luminosity of 4.9 fb(-1), the differential cross-section in the Z/gamma* -> e(+)e(-) channel is measured with the ATLAS detector as a function of the invariant mass, m(ee), in the range 116 < m(ee) < 1500 GeV, for a fiducial region in which both the electron and the positron have transverse momentum p(T) > 25 GeV and pseudorapidity vertical bar n vertical bar < 2.5. A comparison is made to various event generators and to the predictions of perturbative QCD calculations at next-to-next-to-leading order.
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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. (2013). Search for excited electrons and muons in root s=8 TeV proton-proton collisions with the ATLAS detector. New J. Phys., 15, 093011–32pp.
Abstract: The ATLAS detector at the Large Hadron Collider is used to search for excited electrons and excited muons in the channel pp -> ll* -> ll gamma, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb(-1) of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass m(l*). For m(l*) >= 0.8 TeV, the respective upper limits on sigma B(l(*) -> l gamma) are 0.75 and 0.90 fb for the e* and mu* searches. Limits on sigma B are converted into lower bounds on the compositeness scale 3. In the special case where Lambda = m(l*), excited-electron and excited-muon masses below 2.2 TeV are excluded.
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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. (2013). Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector. Physical Review D, 88(7), 072001–22pp.
Abstract: A search is presented for microscopic black holes in a like-sign dimuon final state in proton-proton collisions at root s = 8 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2012 and correspond to an integrated luminosity of 20.3 fb(-1). Using a high track multiplicity requirement, 0.6 +/- 0.2 background events from Standard Model processes are predicted and none observed. This result is interpreted in the context of low-scale gravity models and 95% C.L. lower limits on microscopic black hole masses are set for different model assumptions.
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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. (2013). Performance of jet substructure techniques for large-R jets in proton-proton collisions at root s=7 TeV using the ATLAS detector. J. High Energy Phys., 09(9), 076–83pp.
Abstract: This paper presents the application of a variety of techniques to study jet substructure. The performance of various modified jet algorithms, or jet grooming techniques, for several jet types and event topologies is investigated for jets with transverse momentum larger than 300 GeV. Properties of jets subjected to the mass-drop filtering, trimming, and pruning algorithms are found to have a reduced sensitivity to multiple proton-proton interactions, are more stable at high luminosity and improve the physics potential of searches for heavy boosted objects. Studies of the expected discrimination power of jet mass and jet substructure observables in searches for new physics are also presented. Event samples enriched in boosted W and Z bosons and top-quark pairs are used to study both the individual jet invariant mass scales and the efficacy of algorithms to tag boosted hadronic objects. The analyses presented use the full 2011 ATLAS dataset, corresponding to an integrated luminosity of 4.7 +/- 0.1 fb(-1) from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of root s = 7 TeV.
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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. (2013). Measurement of the production cross section of jets in association with a Z boson in pp collisions at root s=7 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 032–51pp.
Abstract: Measurements of the production of jets of particles in association with a Z boson in pp collisions at root s = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb(-1) collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p(T) > 30 GeV and rapidity vertical bar y vertical bar < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers.
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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. (2013). Search for new phenomena in final states with large jet multiplicities and missing transverse momentum at root s=8 TeV proton-proton collisions using the ATLAS experiment. J. High Energy Phys., 10(10), 130–50pp.
Abstract: A search is presented for new particles decaying to large numbers (7 or more) of jets, with missing transverse momentum and no isolated electrons or muons. This analysis uses 20.3 fb(-1) of p p collision data at root s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The sensitivity of the search is enhanced by considering the number of b-tagged jets and the scalar sum of masses of large-radius jets in an event. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of various simplified supersymmetry-inspired models where gluinos are pair produced, as well as an mSUGRA/CMSSM model.
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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. (2013). Measurement of the Azimuthal Angle Dependence of Inclusive Jet Yields in Pb plus Pb Collisions at root s(NN)=2.76 TeV with the ATLAS Detector. Phys. Rev. Lett., 111(15), 152301–18pp.
Abstract: Measurements of the variation of inclusive jet suppression as a function of relative azimuthal angle, Delta phi, with respect to the elliptic event plane provide insight into the path-length dependence of jet quenching. ATLAS has measured the Delta phi dependence of jet yields in 0.14 nb(-1) of root s(NN) = 2.76 TeV Pb + Pb collisions at the LHC for jet transverse momenta p(T) > 45 GeV in different collision centrality bins using an underlying event subtraction procedure that accounts for elliptic flow. The variation of the jet yield with Delta phi was characterized by the parameter, nu(jet)(2), and the ratio of out-of-plane (Delta phi similar to pi/2) to in-plane (Delta phi similar to 0) yields. Nonzero nu(jet)(2) values were measured in all centrality bins for p(T) < 160 GeV. The jet yields are observed to vary by as much as 20% between in-plane and out-of-plane directions.
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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. (2013). Measurement of the top quark charge in pp collisions at root s=7 TeV with the ATLAS detector. J. High Energy Phys., 11(11), 031–42pp.
Abstract: A measurement of the top quark electric charge is carried out in the ATLAS experiment at the Large Hadron Collider using 2.05 fb(-1) of data at a centre-of-mass energy of 7TeV. In units of the elementary electric charge, the top quark charge is determined to be 0.64 +/- 0.02 (stat.) +/- 0.08 (syst.) from the charges of the top quark decay products in single lepton t (t) over bar candidate events. This excludes models that propose a heavy quark of electric charge -4/3, instead of the Standard Model top quark, with a significance of more than 8 sigma.
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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. (2013). Search for direct third-generation squark pair production in final states with missing transverse momentum and two b-jets in root s=8 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 10(10), 189–40pp.
Abstract: The results of a search for pair production of supersymmetric partners of the Standard Model third-generation quarks are reported. This search uses 20.1 fb(-1) of pp collisions at root s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The lightest bottom and top squarks ((b) over tilde (1) and (t) over tilde (1) respectively) are searched for in a final state with large missing transverse momentum and two jets identified as originating from b-quarks. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the visible cross section for processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of the third-generation squarks are derived in phenomenological supersymmetric R-parity-conserving models in which either the bottom or the top squark is the lightest squark. The (b) over tilde (1) is assumed to decay via (b) over tilde (1) -> b (chi) over tilde (0)(1) and the (t) over tilde (1) via (t) over tilde (1) b (chi) over tilde (+/-)(1), with undetectable products of the subsequent decay of the (chi) over tilde (+/-)(1) due to the small mass splitting between the (chi) over tilde (+/-)(1) and the (chi) over tilde (0)(1)
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