On the small contribution to the Z⁰ width of a new and elusive vector-like down quark singlet

We discuss the small contribution of a new vector-like down quark singlet to the Z0 hadronic width. Such a particle could be somewhat elusive, in particular at large hadron colliders, for it might be hidden in the hadronic background. It is also possible for appropriate values of the new (mass) parameters that this vector-like quark could be detected in missing transverse momentum distributions for pure hadronic events, as well as in dilepton mass distributions for events with no missing transverse momentum. © 1990.