Combined search for the quarks of a sequential fourth generation

Abstract

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 5  fb−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 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about ±20  GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions

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Adair, A., Boulahouache, C., Ecklund, K.M., et al.. "Combined search for the quarks of a sequential fourth generation." Physical Review D, 86, (2012) American Physical Society: 112003. http://dx.doi.org/10.1103/PhysRevD.86.112003.

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