Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay

We report on a search for pair productionof a fourth generation charge -1/3 quark (b{sup {prime}}) in p{ovr p} collisions at {radical}(s)=1.8TeV by the DO/ experiment at the Fermilab Tevatronusing an integrated luminosity of 93pb{sup -1}. Both b{sup {prime}} quarks are assumed to decay via flavor changing neutral currents(FCNC). The search uses the signatures {gamma}+3 jets +{mu}-tag and 2{gamma}+2 jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fractionthat is well below theoretical expectations for a b{sup {prime}} decaying exclusively via FCNC for b{sup {prime}} masses up to m{sub Z}+m{sub b}. {copyright} {ital 1997} {ital The American Physical Society}