"Evidence for Single Top Production at CDF"

Thomas R. Junk, University of Illinois

The top quark, observed at the Tevatron in 1995, has an 
enormous mass -- nearly that of an atom of gold. If it 
behaves like the other five known quarks, it should be 
produced singly in hadron collisions via the weak interaction. 
Measurement of the production rate of weakly produced single 
top quarks provides a direct determination of |Vtb|, which 
can be used to check of the 3x3 unitarity of the CKM matrix. 
Single top quarks also share a final state with one of the 
more powerful search channels for the Standard Model Higgs 
boson at the Tevatron, and the use and careful understanding 
of advanced analysis techniques are needed in order to establish 
evidence for these low-rate processes in the presence of large 
backgrounds with large systematic uncertainties. Two such analyses 
are presented -- a likelihood-function search and a matrix-element 
search. The measured cross section for single top quarks 
is 3.0+1.4-1.2 pb, with a significance of 3.1 standard deviations, 
using the matri  x-element technique, and 2.7+1.3-1.1 for the 
likelihood function technique, with a significance of 2.7 standard 
deviations.