Dzero published today measurements on W+jet events. One can take many lessons out of this measurement and the comparisons to “SM theory” (Figure 3, second panel). The latter is not a unique object and has to be treated with care. The blue and red theory bands correspond to calculations of the same NLO cross-section which agree with each other if identical choices are made for coupling constants, parton densities, electroweak parameters and renormalization and factorization scales. So, both calculations are correct!
Here enters the freedom of physicists, in the form of selecting parameters and especially the renormalization and factorization scales. The blue band corresponds to typically smaller values of the scales than the red and it yields a larger number of W+2jets. D0 measurements seem to agree with this theory prediction pretty well. On the other hand, larger scales as in the red band seem to be quite bad. Notice how poorly the red scale choice underestimates the measured cross-section for let’s say, pt=150GeV/2?
Dzero has not shown a dijet invariant mass in this publication. I would be surprised is this had no bearing on the significance of the Wjj excess at CDF. Unfortunately, their scale choice is not explicitly stated (referred as the Q scale of ALPGEN, and ALPGEN in its manual has more than one options – most of them rather high-ish…). In a recent theory paper with MCFM testing the CDF setup a scale closer to the red choice was used.