Search for pair produced fourth-generation up-type quarks in pp collisions at sqrt(s) = 7 TeV with a lepton in the final state

TL;DR

This paper reports a search for fourth-generation up-type quarks in proton-proton collisions at 7 TeV, setting mass exclusion limits below 570 GeV based on CMS data, with no significant excess observed over standard model predictions.

Contribution

The study provides the first direct experimental limits on pair-produced fourth-generation up-type quarks at the LHC, excluding masses below 570 GeV.

Findings

No significant excess of events observed.

Excluded t'-quark masses below 570 GeV.

Set upper limits on production cross section.

Abstract

The results of a search for the pair production of a fourth-generation up-type quark (t') in proton-proton collisions at sqrt(s) = 7 TeV are presented, using data corresponding to an integrated luminosity of about 5.0 inverse femtobarns collected by the Compact Muon Solenoid experiment at the LHC. The t' quark is assumed to decay exclusively to a W boson and a b quark. Events with a single isolated electron or muon, missing transverse momentum, and at least four hadronic jets, of which at least one must be identified as a b jet, are selected. No significant excess of events over standard model expectations is observed. Upper limits for the t' anti-t' production cross section at 95% confidence level are set as a function of t' mass, and t'-quark production for masses below 570 GeV is excluded. The search is equally sensitive to nonchiral heavy quarks decaying to Wb. In this case, the results can be interpreted as upper limits on the production cross section times the branching fraction to Wb.