Invariant Mass Distribution of Jet Pairs Produced in Association with a   W boson in ppbar Collisions at sqrt(s) = 1.96 TeV
  We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb^-1. The observed distribution has an excess in the 120-160 GeV/c^2 mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this letter we report studies of the properties of this excess. 
CDF Collaboration, T. Aaltonen, et al
hep-ex