Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables

We perform a global fit of the parameters of the Standard Model with a sequential fourth generation (SM4) to LHC and Tevatron Higgs data and electroweak precision data. Using several likelihood ratio tests, we compare the performance of the SM4 and the Standard Model (SM3) at describing the measured data. Since the SM3 and SM4 are not nested (i.e., the SM3 cannot be considered as a special case of the SM4 with some parameters fixed), the usual analytical formulae for p-values in likelihood ratio tests do not hold. We thus apply a new method to compute these p-values. For a Higgs mass of 126.5 GeV and fourth-generation quark masses above 600 GeV, we find that the SM4 is excluded at 3.1σ.