Search for Supersymmetry Using Higgs Boson to Diphoton Decays and Search for Long-Lived Particles Using Out-of-Time Trackless Jets at √s = 13 TeV

Citation

Mao, Jiajing (2023) Search for Supersymmetry Using Higgs Boson to Diphoton Decays and Search for Long-Lived Particles Using Out-of-Time Trackless Jets at √s = 13 TeV. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/pwpe-ef70. https://resolver.caltech.edu/CaltechTHESIS:05302023-234037855

Abstract

The thesis describes two searches conducted at the Large Hadron Collider with a center-of-mass energy of 13 TeV, using proton-proton collison data collected by the CMS experiment. The supersymmetry (SUSY) search focus on the production of at least one Higgs boson that decays into two photons in the decay chains of pair-produced SUSY particles. The data used has an integrated luminosity of 77.5 fb⁻¹. The events are classified into different search regions based on charged leptons, Higgs boson candidates, and kinematic variables to make them sensitive to different SUSY scenarios. The results reveal no statistically significant excess of events compared to the standard model predictions. The searches exclude bottom squark pair production for bottom squark masses below 510 GeV and a lightest SUSY particle mass of 1 GeV. The wino-like chargino-neutralino production in gauge-mediated SUSY breaking (GMSB) is excluded for chargino and neutralino masses below 235 GeV, with a gravitino mass of 1 GeV. Furthermore, the higgsino-like chargino-neutralino production in GMSB, where the neutralino decays exclusively to a Higgs boson and a gravitino, is excluded for neutralino masses below 290 GeV. The thesis also reports a search for long-lived particles that decay in the outer regions of the CMS silicon tracker or in the calorimeters. The search uses data with an integrated luminosity of 138 fb⁻¹. The identification of long-lived particle decays utilizes a novel technique that combines nearly trackless and out-of-time jet information into a deep neural network discriminator. The results are interpreted using a simplified GMSB model of chargino-neutralino production, where the neutralino is the next-to-lightest supersymmetric particle that decays to a gravitino and either a Higgs or Z boson. The search achieves the highest sensitivity for neutralino proper decay lengths of approximately 0.5 meters and excludes masses up to 1.18 TeV at a 95\% confidence level. This search represents the most stringent constraint to date in the mass range from the kinematic limit imposed by the Higgs boson mass up to 1.8 TeV.

Thesis Files