Z'→ggg decay in left-right symmetric models with three and four fermion families

We study the Z'→qq,ggg decays in the context of a manifest left-right symmetric gauge theory with three and four generations. The Z' couplings to quarks are fixed essentially by the parameters of the standard model and we obtain Γ(Z'→qq)≅14 GeV for MZ'≅1 TeV. For the Z'→ggg decay and three families we obtain a branching ratio BR(Z'→ggg)=(Γ(Z'→ggg)/Γ(Z'→qq))=1.2-2.8x10-5 for mZ'=700-1500 GeV. The fourth generation produces an enhancement in the branching ratio for Z' masses close to the b'b' threshold and a dip for Z' masses close to the t't' threshold. Using the values of the fourth-generation quark masses allowed by electroweak precision data, we obtain a branching ratio BR(Z'→ggg)=(1-6)x10-5 for mZ'=(700-1500) GeV.