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

TL;DR

This paper reports a search for a hypothetical fourth-generation charge -1/3 quark decaying via flavor-changing neutral currents in proton-antiproton collisions, finding no evidence and setting upper limits on its production.

Contribution

It introduces a novel search strategy for a fourth-generation b' quark via FCNC decay channels at the Fermilab Tevatron.

Findings

No significant excess of events observed.

Upper limits set on production cross section times branching fraction.

Constraints placed on b' quark masses up to m(Z)+m(b).

Abstract

We report on a search for pair production of a fourth generation charge -1/3 quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron using an integrated luminosity of 93 pb^-1. Both 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 fraction that is well below theoretical expectations for a b' quark decaying exclusively via FCNC for b' quark masses up to m(Z) + m(b).