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) over bar collisions with root 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, p (p) over bar --> T'(T') over bar --> t (t) over bar + X (X) over bar --> bq (q) over bar (b) over bar q (q) over bar + X (X) over bar. We interpret our results in terms of a model where T' is an exotic fourth generation quark and X is a dark matter particle. The data are consistent with standard model expectations. We set a limit on the generic production of T'(T') over bar --> t (t) over bar + X (X) over bar, excluding the fourth generation exotic quarks T' at 95% confidence level up to m(T') = 400 GeV/c(2) for m(X) <= 70 GeV/c(2).
