Search for Higgs boson compositeness effects in high-mass dilepton final states in proton-proton collisions at $\sqrt{s}$ = 13 and 13.6 TeV

Abstract

A search for beyond the standard model effects in high-mass dielectron and dimuon final states with the CMS detector is performed, with a specific focus on Higgs boson compositeness. The search uses data collected at the LHC at 13 and 13.6 TeV center-of-mass energies, corresponding to a total integrated luminosity of 207 fb$^{-1}$. Compositeness would manifest as distortions in the observed dilepton mass spectrum and the presence of bound states, such as the Higgs boson and new massive vector boson resonances. Assuming the existence of new boson states with masses well above the TeV scale, an effective field theory approach provides stringent bounds on the oblique parameters $\mathcal{W}$ and $\mathcal{Y}$, which are zero in the standard model. One-dimensional fits, in which only one of the oblique parameters is allowed to deviate from zero, provide the following limits: $-$3.9 $\times$ 10$^{-4}$$\lt$ $\mathcal{Y}$ $\lt$ 3.5 $\times$ 10$^{-4}$ and $-$2.1 $\times$ 10$^{-4}$ $\lt$ $\mathcal{W}$ $\lt$ 1.6 $\times$ 10$^{-4}$ at 95% confidence level. More stringent compositeness limits at the TeV scale are set in several new physics scenarios under the assumption that a new Z' resonance is physically present within or slightly above the visible dilepton mass spectrum. In this context, cases with large resonance decay widths are explored for the first time.