Percorrer por autor "ATLAS collaboration (3040 authors)"
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- Measurement of inclusive two-particle angular correlations in pp collisions with the ATLAS detector at the LHCPublication . ATLAS collaboration (3040 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; 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; Soares, Mara; Veloso, Filipe; Wolters, HelmutWe present a measurement of two-particle angular correlations in proton-proton collisions at sqrt(s) = 900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum pT > 100 MeV and pseudorapidity |eta| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to Pythia 8 and Herwig++ as well as to the AMBT2B, DW and Perugia 2011 tunes of Pythia 6. The data are not satisfactorily described by any of these models.
- Search for down-type fourth generation quarks with the ATLAS detector in events with one lepton and hadronically decaying $W$ bosonsPublication . ATLAS collaboration (3040 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; 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; Soares, Mara; Veloso, Filipe; Wolters, HelmutThis Letter presents a search for pair production of heavy down-type quarks decaying via b'->Wt in the lepton + jets channel, as b'b'->WtWt->bbWWWW->lvbbqqqqqq. In addition to requiring exactly one lepton, large missing transverse momentum and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04 fb^-1 from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV is excluded at the 95% confidence level.
- Search for excited leptons in proton-proton collisions at $\sqrt{s}=7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (3040 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; 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; Soares, Mara; Veloso, Filipe; Wolters, HelmutThe ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel l* --> l+gamma. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05/fb. No evidence for excited leptons is found, and limits are set on the compositeness scale Lambda as a function of the excited lepton mass m_l*. In the special case where Lambda = m_l*, excited electron and muon masses below 1.87 TeV and 1.75 TeV are excluded at 95% C.L., respectively.
- Search for pair production of a new quark that decays to a Z boson and a bottom quark with the ATLAS detectorPublication . ATLAS collaboration (3040 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; 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, HelmutA search is reported for the pair production of a new quark, b', with at least one b' decaying to a Z boson and a bottom quark. The data, corresponding to 2.0 fb^-1 of integrated luminosity, were collected from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. Using events with a b-tagged jet and a Z boson reconstructed from opposite-charge electrons, the mass distribution of large transverse momentum b' candidates is tested for an enhancement. No evidence for a b' signal is detected in the observed mass distribution, resulting in the exclusion at 95% confidence level of b' quarks with masses m_{b'} < 400 GeV that decay entirely via b' to Z+b. In the case of a vector-like singlet b' mixing solely with the third Standard Model generation, masses m_{b'} < 358 GeV are excluded.