A search for prompt lepton-jets in pp collisions at √s=7TeV with the ATLAS detector
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 719:4-5 (2013) 299-317
Abstract:
We present a search for a light (mass <2GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted "lepton-jets". The analysis uses 5fb-1 of s=7TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model. © 2013 CERN.Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton-proton collisions at √s=7TeV with the ATLAS detector
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 719:4-5 (2013) 280-298
Abstract:
Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at √s=7TeV corresponding to an integrated luminosity of 4.4 fb-1 collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses. © 2013 CERN.Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at s=7TeV with the ATLAS detector
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 718:4-5 (2013) 1284-1302
Abstract:
A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb-1 of pp collisions at s=7TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t't̄' signal when mt'≳400GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t'→Wb)=1, a fourth-generation t' quark with mass lower than 656GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ~126GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t'→Wb) versus BR(t'→Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses. © 2012 CERN.Search for pair-produced massive coloured scalars in four-jet final states with the ATLAS detector in proton–proton collisions at √s =7 TeV
European Physical Journal C 73:1 (2013)
Abstract:
A search for pair-produced massive coloured scalar particles decaying to a four-jet final state is performed by the ATLAS experiment at the LHC in proton–proton collisions at √s = 7 TeV. The analysed data sample corresponds to an integrated luminosity of 4.6 fb−1. No deviation from the Standard Model is observed in the invariant mass spectrum of the two-jet pairs. A limit on the scalar gluon pair production cross section of 70 pb (10 pb) is obtained at the 95 % confidence level for a scalar gluon mass of 150 GeV (350 GeV). Interpreting these results as mass limits on scalar gluons, masses ranging from 150 GeV to 287 GeV are excluded at the 95 % confidence level.Search for direct slepton and gaugino production in final states with two leptons and missing transverse momentum with the ATLAS detector in pp collisions at s=7 TeV
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 718:3 (2013) 879-901