Percorrer por autor "ATLAS collaboration (2887 authors)"
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- Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in $pp$ collisions at $\sqrt{s}$=8 TeVPublication . ATLAS collaboration (2887 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutThis paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy $\sqrt{\mathrm {s}} = 8$ $\,\hbox {TeV}$ . The performance of these algorithms is measured in most cases with $Z$ decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb$^{-1}$ . An uncertainty on the offline reconstructed tau energy scale of 2–4 %, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5 % for hadronically decaying tau leptons with one associated track, and of 4 % for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 $\,\hbox {GeV}$ . For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2–8 %, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton–proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
- Measurements of jet vetoes and azimuthal decorrelations in dijet events produced in $pp$ collisions at $\sqrt{s}=7\,\mathrm{TeV}$ using the ATLAS detectorPublication . ATLAS collaboration (2887 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Do Valle Wemans, André; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Marques, Carlos; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutAdditional jet activity in dijet events is measured using ${pp}$ collisions at ATLAS at a centre-of-mass energy of $7\,\mathrm{TeV}$ , for jets reconstructed using the ${\mathrm{anti}\hbox {-}{k_t}}$ algorithm with radius parameter ${R=0.6}$ . This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijet s. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the scalar average of the transverse momenta of the dijet s and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijet s. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to powheg, interfaced to the pythia 8 and herwig parton shower generators, as well as to hej with and without interfacing it to the ariadne parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered, however, powheg+pythia 8 and hej+ariadne are found to provide the best agreement with the data. These measurements use the full data sample collected with the ATLAS detector in $7\,\mathrm{TeV}$ ${pp}$ collisions at the LHC and correspond to integrated luminosities of $36.1\,\mathrm{pb}^{-1}$ and $4.5\,\mathrm{fb}^{-1}$ for data collected during 2010 and 2011, respectively.
- Search for a Structure in the $B^0_s \pi^\pm$ Invariant Mass Spectrum with the ATLAS ExperimentPublication . ATLAS collaboration (2887 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Castro, Nuno Filipe; Conde Mui\~no, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gon\c calo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Am\'elia; Maneira, Jos\'e; Oleiro Seabra, Luis Filipe; Onofre, Ant\'onio; Pedro, Rute; Santos, Helena; Saraiva, Jo\~ao; Silva, Jos\'e; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→Bs0π±, Bs0→J/ψϕ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb-1 of pp collisions at 7 TeV and 19.5 fb-1 at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to Bs0 mesons, ρX, were determined at 95% confidence level. The results are N(X)<382 and ρX<0.015 for Bs0 mesons with transverse momenta above 10 GeV, and N(X)<356 and ρX<0.016 for transverse momenta above 15 GeV. Limits are also set for potential Bs0π± resonances in the mass range 5550 to 5700 MeV.
- Search for high-mass resonances decaying to dilepton final states in pp collisions at s**(1/2) = 7-TeV with the ATLAS detectorPublication . ATLAS collaboration (2887 authors); Aguilar-Saavedra, Juan Antonio; Anjos, Nuno; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Do Valle Wemans, André; Fiolhais, Miguel; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oliveira, Miguel Alfonso; Onofre, António; Palma, Alberto; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Veloso, Filipe; Wolters, HelmutThe ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to an electron-positron pair or a muon-antimuon pair. The search is sensitive to heavy neutral Z' gauge bosons, Randall-Sundrum gravitons, Z* bosons, techni-mesons, Kaluza-Klein Z/gamma bosons, and bosons predicted by Torsion models. Results are presented based on an analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9/fb in the dielectron channel and 5.0/fb in the dimuon channel. A Z' boson with Standard Model-like couplings is excluded at 95 percent confidence level for masses below 2.22 TeV. A Randall-Sundrum graviton with coupling k/Mbar = 0.1 is excluded at 95 percent confidence level for masses below 2.16 TeV. Limits on the other models are also presented, including Technicolor and Minimal Z' Models.
- Search for supersymmetry at $\sqrt{s}$=8 TeV in final states with jets and two same-sign leptons or three leptons with the ATLAS detectorPublication . ATLAS collaboration (2887 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Do Valle Wemans, André; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Marques, Carlos; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons (e or μ) with the same electric charge, or at least three isolated leptons. The search also utilises jets originating from b-quarks, missing transverse momentum and other observables to extend its sensitivity. The analysis uses a data sample corresponding to a total integrated luminosity of 20.3 fb(−1) of = 8 TeV proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider in 2012. No deviation from the Standard Model expectation is observed. New or significantly improved exclusion limits are set on a wide variety of supersymmetric models in which the lightest squark can be of the first, second or third generations, and in which R-parity can be conserved or violated.