Search for Higgs Boson Decays to Long-Lived Scalar Particles in pp Interactions at 13 TeV

Presented in this thesis are the results of a novel search for exotic particles produced at the Large Hadron Collider (LHC). The search is performed using the data collected by the Compact Muon Solenoid (CMS) detector during the Run II period (2016 - 2018) of data taking. The data corresponds to a total integrated luminosity of 117fb−1, recorded at √s = 13 TeV. The search is performed in the topology where the Higgs boson is produced in association with a Z boson. The Higgs boson may decay to two exotic long-lived scalar particles (S). Final states where the long-lived particle decays to pairs of either b-quarks, d-quarks or τ-leptons are considered. No significant excess in the data with respect to the expected number of events containing decays to long-lived particles was observed. Limits are set on the branching ratio BR(H→SS) for the final states where the long-lived particle decays to pairs of b-quarks or d-quarks. No limit is set for the final state containing decays of the long-lived particles to pairs of τ-leptons. The limits reflect the most stringent results for the decays of the scalar particles to low mass (< 20 GeV) particles with lifetimes in the range 10 < cτ < 100 mm. The branching ratio for the Higgs boson decaying to pairs of long-lived scalar particles which decay to pairs of b-quarks is excluded to be above 15%(4%) at the 95% confidence level for scalar particle masses of 15 GeV(> 40 GeV). The branching ratio for the Higgs boson decaying to pairs of long-lived scalar particles which decay to pairs of d-quarks is excluded to be above 13%(5%) at the 95% confidence level for scalar particle masses of 15 GeV(> 40 GeV). Additionally, these limits reflect the most stringent limits on the branching ratio for the Higgs boson decaying to any exotic particles.