THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS
Abstract
A search for exotic decays of the Higgs boson (H)
with a mass of 125 GeV to a pair of light pseudoscalars a1 is
performed in final states where one pseudoscalar decays to
two b quarks and the other to a pair of muons or τ leptons. A
data sample of proton–proton collisions at √s = 13 TeV cor-
responding to an integrated luminosity of 138 fb−1 recorded
with the CMS detector is analyzed. No statistically signifi-
cant excess is observed over the standard model backgrounds.
Upper limits are set at 95% confidence level (CL) on the
Higgs boson branching fraction to μμbb and to ττbb, via a
pair of a1 s. The limits depend on the pseudoscalar mass ma1
and are observed to be in the range (0.17–3.3) ×10−4 and
(1.7–7.7) ×10−2 in the μμbb and ττbb final states, respec-
tively. 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 a 1 → bb) at 95% CL, with
being a muon or a τ lepton. For different types of 2HDM+S,
upper bounds on the branching fraction B(H → a 1 a1) are
extracted from the combination of the two channels. In most
of the Type II 2HDM+S parameter space, B(H → a 1 a1)
values above 0.23 are excluded at 95% CL for ma1 values
between 15 and 60 GeV
