Oxford Higgs Group

The discovery of a Higgs boson in 2012 was a triumph for both experimental and theoretical particle physics. If the boson is indeed a fundamental scalar, it is the first such particle observed -- perhaps the first of many. Further studies of this boson will address such questions as: Is the Higgs boson a fundamental particle, or a composite particle made from more elementary particles? Is this the only Higgs boson, or do multiple Higgs bosons provide mass to the other particles? Are there new particles, perhaps the dark matter particle, that interact not through the SM forces, but through the Higgs boson alone?

In Run 1 of the LHC the Oxford Higgs group was a leader in searches for Higgs boson decays to W-boson and tau-lepton pairs. The ATLAS discovery paper of 2012 included the results of the search for W-boson pairs, in which Oxford physicists coordinated and determined theoretical normalizations and uncertainties, and developed methods to improve the sensitivity of the measurement. A substantial portion of the summary paper on the Run 1 H->WW results was written by Oxford. Run 1 also provided evidence for the predicted Higgs couplings to tau leptons, with Oxford making important contributions to this measurement.

In Run 2 Oxford have searched for new Higgs bosons decaying to tau-lepton pairs, to Z-boson pairs, and to Higgs-boson pairs. The search in the HH final state will be extended to the SM production of this process, which tests the prediction of the self-coupling of the Higgs boson due to the potential energy described by the Higgs mechanism. Since the cross section for HH production is small, Oxford's searches are performed in the channels with the highest rates, H(->bb)H(->bb) and H(->bb)H(->WW). As more data are collected, Oxford will contribute to the first observation of Higgs boson decays to b-quark pairs, which has the highest branching fraction of all SM decays. Oxford will also enter the search for Higgs boson decays to muon pairs, which would demonstrate the universality of the mass dependence of the Higgs couplings across fermion generations.

Evidence for Higgs decays to W boson pairs: A comparison of data to background plus Higgs signal for a mass-like distribution in final states with two W bosons.ATLAS Higgs measurements: The ratio of measured Higgs-like events to Standard Model prediction in a variety of Higgs boson decay channels.

Projects for students
Measurements of a variety of Higgs boson production processes: gluon-gluon fusion vector-boson fusion associated production with a gauge boson associated production with top quarks
In a variety of decay channels: W-boson pairs Z-boson pairs b-quark pairs muon pairs
Related performance studies jet energy scale missing energy muon calibration and trigger development

Current students

Name Topic
L. Ambroz Search for the SM Higgs boson produced in association with a vector boson and decaying to bb
L. Marchese Determination of the Higgs width using H->ZZ
M. Petrov Measuring the Higgs width and searching for additional Higgs boson in H to ZZ to 2l 2v
C. Tosciri Search for the SM Higgs boson produced in association with a vector boson and decaying to bb
L. Vigani Search for invisible Higgs decays in ZH->2l 2v
G. Zemaityte Measurement of H->WW and constraints on effective field theory parameters
M. Zubgic Search Higgs bosons decaying into di-muons

Former students

Name Topic Year
M. Pickering Search for associated Higgs boson production with decays to tau-lepton pairs 2016
J. Howard Search for Higgs boson decays to tau-lepton pairs 2015
D. Hall Measurement of the Higgs boson in decays to W-boson pairs 2014
C. Boddy Search for the Higgs boson in decays to tau-lepton pairs 2012
A. Larner Search for vector-boson fusion Higgs production with decays to tau-lepton pairs 2012
G. Wooden A Search for H→WW using a Matrix Element Discriminant and a WW Cross Section Measurement at ATLAS 2011

C. Hays, D. Bortoletto, I. Shipsey, T. Weidberg