We present a search for a new particle T' decaying to a
top-quark via T' --> 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 t Fermilab in p anti-p collisions with s**(1/2) ñ.96 TeV, we
search for pair production of T' in the lepton + jets channel, p anti-p
--> tt-bar + XX --> ell nu b qq' b + XX. We interpret our results
primarily in terms of a model where T' are exotic fourth generation quarks
and X are dark matter particles. The data are consistent with standard
model expectations, and we set 95% confidence level limits on the generic
production of T'T-bar' -> tt-bar + XX. We apply these limits to the
dark matter model and exclude the fourth generation exotic quarks T'
at 95% confidence level up to m_T' ó60 GeV/c2 for m_x < 100 GeV/c2.
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Updated: Wednesday, 2011 May 25 11:20:54 CDT automatically from input from "Carol Picciolo"