Professor Chris Hays

Abstract:

This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Standard Model Higgs boson of mass 110≤mH≤130GeV produced in association with a W or Z boson and decaying to bb'. Three decay channels are considered: ZH→ℓ+ℓ-bb', WH→ℓνbb' and ZH→νν'bb', where ℓ corresponds to an electron or a muon. No evidence for Higgs boson production is observed in a dataset of 7TeV pp collisions corresponding to 4.7fb-1 of integrated luminosity collected by ATLAS in 2011. Exclusion limits on Higgs boson production, at the 95% confidence level, of 2.5 to 5.5 times the Standard Model cross section are obtained in the mass range 110-130GeV. The expected exclusion limits range between 2.5 and 4.9 for the same mass interval. © 2012 CERN.

Abstract:

This Letter presents the results of a direct search with the ATLAS detector at the LHC for a Standard Model Higgs boson of mass 110≤m H ≤130GeV produced in association with a W or Z boson and decaying to bb'. Three decay channels are considered: ZH→ℓ+ℓ-bb', WH→ℓνbb' and ZH→νν'bb', where ℓ corresponds to an electron or a muon. No evidence for Higgs boson production is observed in a dataset of 7TeV pp collisions corresponding to 4.7fb -1 of integrated luminosity collected by ATLAS in 2011. Exclusion limits on Higgs boson production, at the 95% confidence level, of 2.5 to 5.5 times the Standard Model cross section are obtained in the mass range 110-130GeV. The expected exclusion limits range between 2.5 and 4.9 for the same mass interval. © 2012 CERN.

Abstract:

A search for doubly charged Higgs bosons decaying to pairs of electrons and/or muons is presented. The search is performed using a data sample corresponding to an integrated luminosity of 4.7 fb−1of pp collisions at √s = 7 TeV collected by the ATLAS detector at the LHC. Pairs of prompt, isolated, high-pT leptons with the same electric charge (e±e±, e±μ±, μ±μ±) are selected, and their invariant mass distribution is searched for a narrow resonance. No significant excess over Standard Model background expectations is observed, and limits are placed on the cross section times branching ratio for pair production of doubly charged Higgs bosons. The masses of doubly charged Higgs bosons are constrained depending on the branching ratio into these leptonic final states. Assuming pair production, coupling to left-handed fermions, and a branching ratio of 100% for each final state, masses below 409 GeV, 375 GeV, and 398 GeV are excluded for e±e±, e±μ±, and μ±μ±, respectively.

Abstract:

A search is presented for the pair production of light scalar top quarks in √s = 7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 running that corresponds to a total integrated luminosity of 4.7 fb−1. Light scalar top quarks are searched for in events with two opposite-sign leptons (e, μ), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through a virtual W boson. If the chargino mass is 106 GeV, light scalar top-quark masses up to 130 GeV are excluded for neutralino masses below 70 GeV.

Abstract:

The b-hadron production cross section is measured with the ATLAS detector in pp collisions at s=7TeV, using 3.3pb -1 of integrated luminosity, collected during the 2010 LHC run. The b-hadrons are selected by partially reconstructing D z.ast;+μ -X final states. Differential cross sections are measured as functions of the transverse momentum and pseudorapidity. The measured production cross section for a b-hadron with p T>9GeV and |n|<2.5 is 32.7±0.8(stat.)-6.8+4.5(syst.)μb, higher than the next-to-leading-order QCD predictions but consistent within the experimental and theoretical uncertainties. © 2012.