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Combined search for the quarks of a sequential fourth generation
Journal article   Open access   Peer reviewed

Combined search for the quarks of a sequential fourth generation

S Chatrchyan, V Khachatryan, A M Sirunyan, A Tumasyan, C Amsler, V Chiochia, S De Visscher, C Favaro, M Ivova Rikova, B Millan Mejias, …
Physical review. D, Particles, fields, gravitation, and cosmology, Vol.86(11), 112003
2012
DOI: 10.1103/PhysRevD.86.112003
url
https://doi.org/10.1103/PhysRevD.86.112003View
Published (Version of record) Open Access

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.
 Physics Physics Institute

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