2021 Theses Doctoral

A Search for Heavy Resonances Decaying to 𝐻𝐻 → 𝑏𝑏̄𝑏𝑏̄ with the ATLAS Detector

Emerman, Alexander Zack

A search for Higgs boson pairs produced in the decay of high mass exotic resonances is presented. The search uses the 𝑏𝑏̄𝑏𝑏̄ final state, analyzing 139 fb⁻¹ of proton–proton collision data at √s = 13 TeV collected with the ATLAS detector. Spin-0 and spin-2 benchmark signal models are considered and no significant deviation from the Standard Model prediction is observed. The search is combined with a complementary analysis for lower mass resonances to set upper limits on the production cross-section times 𝐻𝐻 branching ratio of new resonances in the mass range of 251 GeV to 5 TeV.

In addition, the methodology for the in-situ calibration of a novel double-𝑏-tagging algorithm (Xbb2020) using gluon to 𝑏𝑏̄ decays is presented. Preliminary scale factors for Monte-Carlo simulation are computed using 139 fb⁻¹ of √s = 13 TeV 𝑝𝑝 collision data collected with the ATLAS detector. The completed calibration will allow the Xbb2020 algorithm to be used in future ATLAS searches for 𝐻 → 𝑏𝑏̄ decays.