Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the μμbb and ττbb 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 a(1) is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or tau leptons. A data sample of proton-proton collisions at root 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 mu mu bb and to tau tau bb, via a pair of a(1)s. The limits depend on the pseudoscalar mass m(a1) and are observed to be in the range (0.17-3.3) x10(-4) and (1.7-7.7) x10(-2) in the mu mu bb and tau tau 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 upper limits on the branching fraction B(H -> a(1)a(1) -> llbb) at 95% CL, with l being a muon or a tau lepton. For different types of 2HDM+S, upper bounds on the branching fraction B(H -> a(1)a(1)) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, B(H -> a(1)a(1)) values above 0.23 are excluded at 95% CL for m(a1) values between 15 and 60 GeV.