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Combined search for the quarks of a sequential fourth generation

par Chatrchyan, Serguei;Clerbaux, Barbara ;De Lentdecker, Gilles ;Gay, Arnaud ;Hreus, Tomas ;Leonard, Alexandre ;Marage, Pierre ;Reis, Thomas ;Thomas, Laurent ;Vander Velde, Catherine ;Vanlaer, Pascal ;Wang, Jian ;Dero, Vincent ; [et al.]
Référence Physical review. D, Particles, fields, gravitation, and cosmology, 86, 11, 112003
Publication Publié, 2012

Article révisé par les pairs

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Résumé :

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5fb-1 recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about ±20GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.