Search for single top quark production at CDF

In proton-antiproton collisions at the Fermilab Tevatron collider, individual top quarks are expected to be produced in association with bottom quarks mainly through the $s$-channel exchange of an off-shell $W$\ boson and also in the $W$-gluon fusion process, called the $t$-channel process. Three searches are conducted -- one separately for an $s$-channel signal, one for a $t$-channel signal, and a combined search. No evidence for electroweak single top quark production is found. Upper limits are placed at the 95\% confidence level at 13.6~pb for the $s$-channel process, 10.1~pb for the $t$-channel process, and 17.8~pb for the sum of the $s$- and $t$-channel processes. Efforts are underway to use more kinematic features of the events in order to separate the signal from background and improve the sensitivity of the searches.