Baryonic Z' Explanation for the CDF Wjj Excess

Kingman Cheung, Jeonghyeon Song

Published 2011-04-07, updated 2011-05-19Version 3

The latest CDF anomaly, the excess of dijet events in the invariant-mass window 120-160 GeV in associated production with a $W$ boson, can be explained by a baryonic $Z'$ model in which the $Z'$ boson has negligible couplings to leptons. Although this $Z'$ model is hardly subject to the Drell-Yan constraint from Tevatron, it is constrained by the dijet data from UA2 ($\sqrt{s} = 630$ GeV), and the precision measurements at LEP through the mixing with the SM $Z$ boson. We show that under these constraints this model can still explain the excess in the M_{jj} \sim 120 - 160 GeV window, as well as the claimed cross section $\sigma(W Z') \sim 4$ pb. Implications at the Tevatron would be the associated production of $\gamma Z',\; Z Z'$, and $Z'Z'$ with the $Z' \to jj$. We show that with tightened jet cuts and improved systematic uncertainties both $\gamma Z' \to \gamma jj$ and $Z Z' \to \ell^+ \ell^- j j$ channels could be useful to probe this model at the Tevatron.