FERMILAB TEVATRON MASS LIMITS FOR HEAVY QUARKS DECAYING VIA FLAVOR-CHANGING NEUTRAL CURRENTS

The dimuon and dielectron data from the Fermilab Tevatron ppBAR collid er are used to probe for heavy quarks, which decay dominantly via flav or-changing neutral currents (FCNC's). Depending on whether the FCNC d ecay occurs at the tree or loop level, one gets a lower mass limit of 85 or 75 GeV. The former applies to singlet, vector doublet, and mirro r-type quarks while the latter applies to a left-handed quark doublet of the fourth generation.