We present a search for a new particle T ＼ decaying to a top quark via T ＼ ⊇ t +X, where X goes
undetected. We use a data sample corresponding to 5.7 fb?1 of integrated luminosity of p≤p collisions
with ∇s = 1.96 TeV, collected at Fermilab Tevatron by the CDF II detector. Our search for pair
production of T ＼ is focused on the hadronic decay channel, pp≤⊇ T ＼T≤＼ ⊇ t≤t+X ≤X ⊇ bq≤q≤bq≤q +X ≤X .
We interpret our results in terms of a model where T ＼ is an exotic fourth generation quark and X is
a dark matter particle.