A Search for Dark Matter via Higgs Decay Using Quark Jet Substructure

Open Access
Abercrombie, Daniel Robert
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Sarah Shandera, Thesis Supervisor
  • Dr. Richard Wallace Robinett, Honors Advisor
  • Higgs boson
  • dark matter
  • invisible Higgs
  • quark jet
  • jet substructure
  • N-Subjettiness
  • Large Hadron Collider
The discovery of a Higgs-like boson has allowed the possibility to probe many models of physics beyond the Standard Model. In this thesis, the possibility of the Higgs decaying into invisible dark matter through $WH \rightarrow q \bar{q} \chi\chi$ is explored. There are two main goals of this thesis. First, reconstruction of the hadronic $W$ is optimized. The main figures of merit for this were the consistency of mass measurements for different collision conditions, and the resolution of this mass measurement. Consistent values allows for the missing energy from the invisible Higgs to be more accurately and quickly measured. Final results in suggest that one of the smaller cone sizes in the study, $\Delta R = 0.4$, will give the best mass resolution without losing too much $p_T$ from radiated particles outside the jet cone. The trimming and filtering grooming algorithms, compete for the best mass resolution, while pruning, the recent CMS default, appears to be an overly aggressive grooming algorithm. The second goal of this thesis is to recommend cuts on the recently proposed jet substructure descriptor N-Subjettiness, to be used in future searches for dark matter at high energy collider experiments. Using cone sizes $\Delta R > 0.9$ with cuts on the N-Subjettiness variables of $\tau_2/\tau_1 < 0.44$ appears to give the best signal significance in this preliminary analysis. Using this jet selection has a clearly visible signal region for Higgs to invisible particles. The excess number of events with the current integrated luminosity is not great enough to claim detection of an invisible Higgs. However, increasing the luminosity in the upcoming run of the LHC will allow this decay channel to be investigated much more conclusively.