Higgs precision study of the 750 GeV diphoton resonance and the 125 GeV standard model Higgs boson with Higgs-singlet mixing

We interpret the potential observation of the 750 GeV diphoton resonance at the LHC in models, in which an SU(2) isospin-singlet scalar boson mixes with the standard model (SM) Higgs boson through an angle alpha. Allowing the singlet scalar boson to have renormalizable couplings to vectorlike leptons and quarks and introducing sizable decay width of the 750 GeV diphoton resonance into non-SMparticles such as dark matters, we can explain the large production cross section sigma(H-2) x B(H-2 -> gamma gamma) as well as the apparent large total width of the boson without conflicts from the results obtained by previous global fits to the SM Higgs boson data.