Study of high-pT Higgs boson production in the b¯b decay channel and calibration of the X → b¯b tagger with the ATLAS detector
- Resource Type
- Electronic Thesis or Dissertation
- Authors
- Jones, Eleanor
- Source
- Subject
- QC Physics
- Language
- English
The study of Higgs boson properties has been a focus of particle physics experiments since its discovery in 2012. Despite huge progress, there are still a number of theoretical predictions yet to be experimentally confirmed and several regions of phase space that remain unexplored. Higgs bosons produced with large transverse momentum is one such region and could offer a window into potential New Physics. This thesis presents a study of Higgs bosons with transverse momentum above 250 GeV in the bottom quark-antiquark decay channel. In particular, the first ATLAS constraints on the cross section for Higgs boson production with pT > 1TeV are reported. The 95% confidence level upper limit on the cross section for Higgs boson production above 1TeV is 9.6 fb compared to the Standard Model prediction of 0.13 fb. In this boosted regime, the experimental signature of the decay is a large radius jet that contains the two b-hadron decays within it. The performance of standard b-taggers that rely on reconstructing and resolving the subjets within the large-radius jet degrades as the transverse momentum of the system increases. The X → b ̄b tagger in ATLAS was developed to improve the efficiency of b-tagging in this extreme regime. This thesis additionally presents a calibration for the X → b ̄b tagger using Zγ and Z + jets events, the first of its kind in ATLAS. The results for the first round of the calibration measured data to simulation efficiency scale factors as a function of the large-radius jet transverse momentum. A second round of the calibration is in progress at the time of writing of this thesis and the latest developments are also presented.