Combined search for the quarks of a sequential fourth generation

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Chatrchyan, S.
Khachatryan, V.
Sirunyan, A. M.
Tumasyan, A.
Adam, W.
Aguilo, E.
Bergauer, T.
Dragicevic, M.
Erö, J.
Fabjan, C.

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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. © 2012 CERN.



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Physical Review D - Particles, Fields, Gravitation and Cosmology, v. 86, n. 11, 2012.