Professor Claire Gwenlan

Abstract:

© 2012 CERN. Published by Elsevier B.V. A search for the Standard Model Higgs boson in proton-proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb -1 collected at √s = 7 TeV in 2011 and 5.8 fb -1 at √s = 8 TeV in 2012. Individual searches in the channels H → ZZ(*) → 4l, H → γγ and H → WW(*) eνμν in the 8 TeV data are combined with previously published results of searches for H → ZZ (*) , WW (*) , bb and τ + τ - in the 7 TeV data and results from improved analyses of the H → ZZ(*) →4l and H → γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of 126.0±0.4 (stat)±0.4 (sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10 -9 , is compatible with the production and decay of the Standard Model Higgs boson.

Abstract:

The results of a search for the production of second generation scalar leptoquarks are presented for final states consisting of either two muons and at least two jets or a muon plus missing transverse momentum and at least two jets. A total of 1.03 fb⁻¹ integrated luminosity of protonproton collision data produced by the Large Hadron Collider at √s = 7 TeV and recorded by the ATLAS detector is used for the search. The event yields in the signal regions are found to be consistent with the Standard Model background expectations. The production of second generation leptoquarks is excluded for a leptoquark mass mLQ < 594 (685) GeV at 95 % confidence level, for a branching ratio of 0.5 (1.0) for leptoquark decay to a muon and a quark.

Abstract:

A search for a fermiophobic Higgs boson using diphoton events produced in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV is performed using data corresponding to an integrated luminosity of 4. 9 fb-1 collected by the ATLAS experiment at the Large Hadron Collider. A specific benchmark model is considered where all the fermion couplings to the Higgs boson are set to zero and the bosonic couplings are kept at the Standard Model values (fermiophobic Higgs model). The largest excess with respect to the background-only hypothesis is found at 125. 5 GeV, with a local significance of 2. 9 standard deviations, which reduces to 1. 6 standard deviations when taking into account the look-elsewhere effect. The data exclude the fermiophobic Higgs model in the ranges 110. 0-118. 0 GeV and 119. 5-121. 0 GeV at 95 % confidence level. © 2012 CERN for the benefit of the ATLAS collaboration.

Abstract:

A search for resonant production of high-mass top-quark pairs is performed on 2.05 fb^-1 of proton-proton collisions at sqrt(s) = 7 TeV collected in 2011 with the ATLAS experiment at the Large Hadron Collider. This analysis of the lepton+jets final state is specifically designed for the particular topology that arises from the decay of highly boosted top quarks. The observed ttbar invariant mass spectrum is found to be compatible with the Standard Model prediction and 95% credibility level upper limits are derived on the ttbar production rate through new massive states. An upper limit of 0.7 pb is set on the production cross section times branching fraction of a narrow 1 TeV resonance. A Kaluza-Klein gluon with a mass smaller than 1.5 TeV is excluded.