Abstract
A search for an exotic decay of the Higgs boson to a pair of light pseudoscalar bosons is performed for the first time in the final state with two b quarks and two τ leptons. The search is motivated in the context of models of physics beyond the standard model (SM), such as two Higgs doublet models extended with a complex scalar singlet (2HDM + S), which include the next-to-minimal supersymmetric SM (NMSSM). The results are based on a data set of proton–proton collisions corresponding to an integrated luminosity of 35.9fb−1, accumulated by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13TeV. Masses of the pseudoscalar boson between 15 and 60GeV are probed, and no excess of events above the SM expectation is observed. Upper limits between 3 and 12% are set on the branching fraction B(h→aa→2τ2b) assuming the SM production of the Higgs boson. Upper limits are also set on the branching fraction of the Higgs boson to two light pseudoscalar bosons in different 2HDM + S scenarios. Assuming the SM production cross section for the Higgs boson, the upper limit on this quantity is as low as 20% for a mass of the pseudoscalar of 40GeV in the NMSSM.
Highlights
Within the standard model (SM), the Brout–Englert–Higgs mechanism [1,2,3,4,5,6] is responsible for electroweak symmetry breaking and predicts the existence of a scalar particle—the Higgs boson
The first search for exotic decays of the Higgs boson to pairs of light bosons with two b quark jets and two τ leptons in the final state has been performed with 35.9 fb−1 of data collected at
13 TeV center-of-mass energy in 2016. This decay channel has a large branching fraction in many models where the couplings to fermions are proportional to the fermion mass, and can be triggered with high efficiency in the dominant gluon fusion production mode because of the presence of light leptons from leptonic τ decays
Summary
Within the standard model (SM), the Brout–Englert–Higgs mechanism [1,2,3,4,5,6] is responsible for electroweak symmetry breaking and predicts the existence of a scalar particle—the Higgs boson. An interesting class of such processes consists of decays to a pair of light pseudoscalar particles, which decay to pairs of SM particles This type of process is allowed in various models, including two Higgs doublet models augmented by a scalar singlet (2HDM + S). The branching fractions of the light pseudoscalars to pairs of SM particles depend on the type of 2HDM + S, on the pseudoscalar mass ma, and on tan β, defined as the ratio of the vacuum expectation values of the second and first doublets. This Letter reports on the first search with the CMS experiment for exotic decays of the Higgs boson to a pair of light pseudoscalar bosons, in the final state with two τ leptons and two b quarks. The ee and μμ final states for the τ τ pair are not considered either, because they have a low branching fraction and suffer from a large contribution of Drell–Yan background events
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