Read the paper: EXO-11-005

In this Letter, CMS describes a search for a kind of fourth-generation T quark with charge 2/3. The search for T-antiT pairs was performed in events that had a pair of oppositely charged leptons (l⁺l⁻) as well as an additional isolated charged lepton.

T-quarks with a mass of less than 475 GeV/c² are excluded with a 95% confidence level.

If it were to exist, the T-quark would decay into either a t-quark and a Z boson (T → tZ) or a t-quark and a Higgs boson (T → tH). However, if the Higgs were too heavy, the first decay would take place almost 100% of the time, as has been assumed in this search. The event selection used depends on one Z from the T-antiT pair decaying into two leptons, while one W (from the decay of one of the t-quarks) must decay into a lepton and a neutrino which escapes undetected.

Decay path: pp → TTX, with TT → (tZ)(tZ) → (bW⁺Z)(bW⁻Z)

Group: Exotica (EXO)
Collisions: pp
Centre-of-mass energy: 7 TeV
Data sample: 1.14 ± 0.05 fb⁻¹
Dates of data collection: March 2011 – June 2011
Measurement/Limit:
Assuming they decay to tZ 100% of the time, T-quarks with a mass of less than 475 GeV/c² are excluded with a 95% confidence level.
Submitted to: Physical Review Letters