Measurement of the mass difference between top and anti-top quarks in pp collisions at √s = 7 TeV using the ATLAS detector

A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb1 data sample of proton-proton collisions at√s = 7 TeV recorded with the ATLAS detector at the LHC, events consistent with tt production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields δm = mt - mt = 0.67 ± 0.61 (stat) ± 0.41 (syst) GeV, consistent with CPT invarianc

Erratum to: “Search for first generation scalar leptoquarks in pp collisions at with the ATLAS detector” [Phys. Lett. B 709 (2012) 158]

Contains fulltext : 93839.pdf (publisher's version ) (Open Access

Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at, root s=8 TeV with the ATLAS detector

A search for Higgs boson decays to invisible particles is performed using 20,3 of fb(-1) collision data at a centre-of-mass energy of 8 TeV recorded by the ArL As detector at the Large IHIadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115 < m(H) < 300 GeV. The 95 % confidence-level observed upper limit on sigma vH x BR(H -> inv.) varies from 1.6 pb at 115 GeV to 0.13 ph at 300 GeV. Assuming Standard Model production and including the gg -> H contribution as signal, the results also lead to an observed upper limit of 78 c/c at 95 % confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV

Jet mass and substructure of inclusive jets in sqrt(s) = 7 TeV pp collisions with the ATLAS experiment

See paper for full list of authors - 30 pages plus author list (53 pages total), 17 figures, submitted to Journal of High Energy PhysicsRecent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb^-1 of pp collisions delivered by the LHC at sqrt(s) = 7 TeV. In a subsample of events with single pp collisions, measurementes corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, kt splitting scales and n-subjettiness variables are presented for anti-kt R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored