Search for Top-Quark Partners with Charge $5/3$ in the Same-Sign Dilepton Final State

A search for the production of heavy partners of the top quark with charge $5/3$ is performed in events with a pair of same-sign leptons. The data sample corresponds to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$ and was collected at $\sqrt{s}=8\mathrm{TeV}$ by the CMS experiment. No significant excess is observed in the data above the expected background, and the existence of top-quark partners with masses below 800 GeV is excluded at a 95% confidence level, assuming they decay exclusively to $tW$. This is the first limit on these particles from the LHC, and it is significantly more restrictive than previous limits.

Figure 1

The distribution of $H_T$ for all channels combined after the full selection except for the $H_T$ requirement itself. The shaded band represents the total uncertainty in the predicted backgrounds. The final bin includes all overflow events. The pull is defined as the difference between the observed and expected values divided by the total uncertainty.

Figure 2

Expected and observed 95% C.L. limits on the $T_{5/3}$ production cross section times the branching fraction for decay to same-sign dileptons. The $1\sigma$ and $2\sigma$ combined statistical and systematic expected variations are shown as yellow (light) and green (dark) bands, respectively.