The Rare Top Decays t → bW + Z and t → cW + W − UCSD/PTH 96–28 hep-ph/9612211

The large value of the top quark mass implies that the rare top decays t → bW+Z, sW+Z and dW+Z, and t → cW+W− and uW+W−, are kinematically allowed decays so long as mt ≥ mW +mZ +mdi ≈ 171.5 GeV+mdi or mt ≥ 2mW + mu,c ≈ 160.6 GeV + mu,c, respectively. The partial decay widths for these decay modes are calculated in the standard model. The partial widths depend sensitively on the precise value of the top quark mass. The branching ratio for t → bW+Z is as much as 2 × 10−5 for mt = 200 GeV, and could be observable at LHC. The rare decay modes t → cW+W− and uW+W− are highly GIM-suppressed, and thus provide a means for testing the GIM mechanism for three generations of quarks in the u, c, t sector.