Search for a fourth generation charge -1/3 quark via flavor changing neutral current decay

Abstract

We report on a search for pair production of a fourth generation charge -1/3 quark (b') in pp̅ collisions at √s=1.8 TeV by the DØ experiment at the Fermilab Tevatron using an integrated luminosity of 93 pb^-1. Both b' quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures γ+3jets+ μ-tag and 2γ+2jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fraction that is well below theoretical expectations for a b' decaying exclusively via FCNC for b' masses up to m_Z+m_b.