Professor Chris Hays

Abstract:

We present a search for the standard model Higgs boson produced in association with a Z boson in data collected with the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45fb-1. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electron or muon pairs, we set 95% credibility level upper limits on the ZH production cross section times the H→bb̄ branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125GeV/c2, we observe (expect) a limit of 7.1 (3.9) times the standard model value. © 2012 American Physical Society.

Abstract:

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at √s=1.96TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45fb-1. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a b quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and 150GeV/c2. For a Higgs boson mass of 125GeV/c2, the observed (expected) limit is 6.7 (3.6) times the standard model prediction. © 2012 American Physical Society.

Abstract:

We combine the results of searches for the standard model Higgs boson based on the full CDF Run II data set obtained from √s = 1.96 TeV pp¯ collisions at the Fermilab Tevatron corresponding to an integrated luminosity of 9.45 fb−1. The searches are conducted for Higgs bosons that are produced in association with a W or Z boson, have masses in the range 90–150 GeV/c2, and decay into b¯b pairs. An excess of data is present that is inconsistent with the background prediction at the level of 2.5 standard deviations (the most significant local excess is 2.7 standard deviations).

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.