Search for Production of Heavy Particles Decaying to Top Quarks and Invisible Particles in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

Understand

We present a search for a new particle $T'$ decaying to top quark via $T^{\prime} \rightarrow t + X$, where $X$ is an invisible particle.

• In a data sample with 4.8 fb$^{-1}$ of integrated luminosity collected by the CDF II detector at Fermilab in $p\bar{p}$ collisions with $\sqrt{s}=1.96$ TeV, we search for pair production of $T'$ in the lepton+jets channel, $p\bar{p} \rightarrow t\bar{t} +X+X \rightarrow \ell\nu b q q' b + X +X$.
• We interpret our results primarily in terms of a model where $T'$ are exotic fourth generation quarks and $X$ are dark matter particles.
• Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV$/c^2$, the dark matter particle mass being anywhere below $m_{T^{\prime}}$.