Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the b b and b b final states

A search for exotic decays of the Higgs boson ( H H ) with a mass of 125 \,Ge-.08emV Ge V to a pair of light pseudoscalars a₁ a 1 is performed in final states where one pseudoscalar decays to two b b quarks and the other to a pair of muons or τ τ leptons. A data sample of proton–proton collisions at √s=13\,Te-.08emV s = 13 Te V corresponding to an integrated luminosity of 138 \,fb⁻¹ 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 CL ) on the Higgs boson branching fraction to b b μ μ b b and to b b , τ τ b b , via a pair of a₁ a 1 s. The limits depend on the pseudoscalar mass m_a₁ m a 1 and are observed to be in the range (0.17–3.3) × 10⁻⁴ × 10 - 4 and (1.7–7.7) × 10⁻² × 10 - 2 in the b b μ μ b b and b b τ τ b b 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 → a₁ a₁ → b b) B ( H → a 1 a 1 → ℓ ℓ b b ) at 95% CL CL , with ℓ being a muon or a τ lepton. For different types of 2HDM+S, upper bounds on the branching fraction B(H → a₁ a₁ ) 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 → a₁ a₁ ) B ( H → a 1 a 1 ) values above 0.23 are excluded at 95% CL CL for m_a₁ m a 1 values between 15 and 60 \,Ge-.08emV Ge V .