Search for a very light NMSSM Higgs boson produced in decays of the 125 GeV scalar boson and decaying into τ leptons in pp collisions at √s=8 TeV

A search for a very light Higgs boson decaying into a pair of τ leptons is presented within the framework of the next-to-minimal supersymmetric standard model. This search is based on a data set corresponding to an integrated luminosity of 19.7 fb⁻¹ of proton-proton collisions collected by the CMS experiment at a centre-of-mass energy of 8 TeV. The signal is defined by the production of either of the two lightest scalars, h₁ or h₂, via gluon-gluon fusion and subsequent decay into a pair of the lightest Higgs bosons, a₁ or h₁. The h₁ or h₂ boson is identified with the observed state at a mass of 125 GeV. The analysis searches for decays of the a₁ (h₁) states into pairs of τ leptons and covers a mass range for the a₁ (h₁) boson of 4 to 8 GeV. The search reveals no significant excess in data above standard model background expectations, and an upper limit is set on the signal production cross section times branching fraction as a function of the a₁ (h₁) boson mass. The 95% confidence level limit ranges from 4.5 pb at m_a1(m_h1) = 8 GeV to 10.3 pb at m_a1(m_h1)=5 GeV.