This result has been known to all blog readers since yesterday, now it's officially out. The D0 collaboration just released a new analysis of the dijet invariant mass spectrum in W+2j events using 4.3 fb-1 of data. Recall that CDF, looking at the same final state, saw an unexpected bump in the dijet spectrum near 150 GeV which might be a sign of new physics beyond the Standard Model. D0 closely follows the CDF analysis. Their conclusion: no bump.
They place the 95% CL limit on the cross section of a hypothetical 145 GeV dijet resonance at the level of 2 picobarns. On the other hand, CDF estimates that fitting their signal requires a larger cross section, of order 4 picobarns, which D0 excludes at 4 sigma. It's not straightforward to draw firm conclusions from these numbers. Although both experiments use almost identical kinematic cuts, they have different detector response, quality cuts, etc., which leads to different results. For example, D0 has about 30% more events than CDF near 150 GeV (after scaling with luminosity). It would be illuminating to run realistic models explaining the CDF bump through both detector simulations in order to compare the efficiencies. That would allow us to quantify the discrepancy between CDF in D0 (it may well be much smaller than 4 sigma). In any case, not seeing any excess in the D0 data puts a lot of strain on any new physics explanation of the CDF excess.
For the moment I don't see any catch in the D0 analysis. Previously, D0 employed differential reweighting to model the W+jets background which might have scaled away any excess; however, the present analysis avoids this step. Also, the D0 data match the Standard Model predictions much better than the CDF ones, also away from the 150 GeV region, which suggests they have backgrounds under better control. Looking closer at the plots, it seems the main difference between the 2 experiments is their estimate of the QCD multijet contribution (kudos to Jay for that observation), but at this point it is not clear if this can explain the CDF bump.
In conclusion, the 2 Tevatron experiments got into an epic standoff. One holds 4 aces in his hand. The other says it's a cheat. We need a shootout to decide who's right :-)
The story is of course all over blogs, see e.g. Tommaso, Michael, Georgios, Peter, Lubos, Sean for more coverage.