Rb, Rc and Jet Distributions at the Tevatron in a Model with an extra   vector boson
  We show that the reported anomalies in $R_b$ and $R_c$ can be interpreted as the effect of a heavy vector boson \zprime\ universally coupled to $u$- and $d$-type quarks separately and nearly decoupled from leptons. This extra vector boson could then also naturally explain the apparent excess of the jet rate at large transverse momentum observed at CDF. 
G. Altarelli, N. Di Bartolomeo, F. Feruglio, R. Gatto, M. Mangano