Joint analysis of Higgs boson decays and electroweak precision observables in the standard model with a sequential fourth generation

Abstract

We analyze the impact of LHC and Tevatron Higgs data on the viability of the standard model with a sequential fourth generation, assuming Dirac neutrinos and a Higgs mass of 125 GeV. To this end we perform a combined fit to the signal cross sections of $pp\ensuremath{\rightarrow}H\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$, $Z{Z}^{*}$, $W{W}^{*}$ at the LHC, to $p\overline{p}\ensuremath{\rightarrow}VH\ensuremath{\rightarrow}Vb\overline{b}$ ($V=W$, $Z$) at the Tevatron and to the electroweak precision observables. Fixing the mass of the fourth-generation down-type quark ${b}^{\ensuremath{'}}$ to 600 GeV we find best-fit values of ${m}_{{t}^{\ensuremath{'}}}=632\text{ }\text{ }\mathrm{GeV}$, ${m}_{{l}_{4}}=113.6\text{ }\text{ }\mathrm{GeV}$ and ${m}_{{\ensuremath{\nu}}_{4}}=58.0\text{ }\text{ }\mathrm{GeV}$ for the other fourth-generation fermion masses. We compare the ${\ensuremath{\chi}}^{2}$ values and pulls of the different observables in the three- and four-generation case and show that the data is better described by the three-generation standard model. We also investigate the effects of mixing between the third- and fourth-generation quarks and of a future increased lower bound on the fourth-generation charged lepton mass of 250 GeV.