Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the $\hat{I}¼\hat{I}¼$bb and $\ddot{I}„\ddot{I}„$bb final states

Abstract

A search for exotic decays of the Higgs boson (H) with a mass of 125 GeV to a pair of light pseudoscalars ${\mathrm{a}}_1$ is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or $\ddot{I}„$ leptons. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 138 fb${}^{-1}$ recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (CL) on the Higgs boson branching fraction to $\hat{I}¼\hat{I}¼$bb and to $\ddot{I}„\ddot{I}„$bb, via a pair of ${\mathrm{a}}_1$s. The limits depend on the pseudoscalar mass $m_{{\mathrm{a}}_1}$ and are observed to be in the range (0.17-3.3) $\times$ 10${}^{-4}$ and (1.7-7.7) $\times$ 10${}^{-2}$ in the $\hat{I}¼\hat{I}¼$bb and $\ddot{I}„\ddot{I}„$bb final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine model-independent upper limits on the branching fraction $\mathcal{B}$(H $\to$ ${\mathrm{a}}_1{\mathrm{a}}_1$ $\to$ $\ell \ell$bb) at 95% CL, with $\ell$ being a muon or a $\ddot{I}„$ lepton. For different types of 2HDM+S, upper bounds on the branching fraction $\mathcal{B}$(H $\to$ ${\mathrm{a}}_1{\mathrm{a}}_1$) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, $\mathcal{B}($H $\to$ ${\mathrm{a}}_1{\mathrm{a}}_1$) values above 0.23 are excluded at 95% CL for $m_{{\mathrm{a}}_1}$ values between 15 and 60 GeV.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIG-22-007 (CMS Public Pages)