Search for Exotic Higgs Decays at CMS and the CMS High Granularity Calorimeter upgrade for HL-LHC

Although the 125 GeV Higgs scalar displays spin, parity, and fermionic and bosonic couplings consistent with those predicted by the Standard Model (SM), constraints on its branching ratio to invisible or non-SM final states are only at the 20-30% level. Direct searches for Higgs decays to non-SM final states offer further insights into the structure of the Higgs sector, specifically whether it consists of the single doublet of the Standard Model, or multiple doublets as proposed by many theories that extend the Standard Model. In this talk, I will present recent results on searches using data collected by the Compact Muon Solenoid (CMS) detector for Higgs decays to non-SM final states, focusing on decays that proceed via new light Higgs states.

The CMS HGCal is a sampling calorimeter constructed of alternating layers of active material and stainless steel absorber. In the regions of highest expected total ionizing dose, silicon is used as active material, while elsewhere plastic scintillator tiles coupled to silicon photomultipliers (SiPMs) are used. It features unprecedented transverse and longitudinal segmentation for both electromagnetic and hadronic compartments. It will replace the current endcap electromagnetic and hadronic calorimeters in the high luminosity LHC starting in 2027. The latest results for the HGCal software and hardware developments and tests will also be discussed.