UC Davis

This dissertation presents a search for a light pseudoscalar Higgs boson in the ${\mathrm{H}\to \mathrm{aa} \to \mu\mu\tau\tau}$ decay channel using the full Run 2 dataset collected by the CMS detector at CERN. Due to the mass difference between the Higgs boson and the pseudoscalar Higgs boson, the final state particles have a boosted topology that includes overlapping $\tau$ decays. The search is performed for the fully hadronic, semi leptonic, and fully leptonic decays of the $\tau$ leptons. DeepDiTau, a tagger trained through machine learning, is used to identify $\tau_{h}\tau_{h}$ decays that are reconstructed as jets. The expected limits on $\sigma_{H}\mathcal{B}(\mathrm{H}\to \mathrm{aa}\to\mu\mu\tau\tau)/\sigma_{SM}$ for all channels in this search are presented.