No new particle after all: Tevatron's second detector comes up empty

The signal from any new particles at 145GeV (dashed line) does not seem to exist.


The excitement that has been building regarding a possible new particle spotted in the Tevatron detector has been seriously dampened. The Tevatron's second detector, DZero, has now repeated the analysis performed by the CDF team and come up empty. That, combined with early indications that nothing at the right mass has been seen at the LHC, suggests there may be something distinct to the CDF detector or the analysis performed by its team that is creating a signal, not an actual particle.

The possible particle appeared in an analysis of collisions that produce a W boson. These events normally produce lots of other particles through processes explained by the Standard Model, all of which have to be subtracted as background. This procedure requires extensive modeling of both the Standard Model background and the particles' interactions with the detector. Once this was done and the background was subtracted, the CDF team saw a bump in its data at a mass of roughly 145GeV, which doesn't correspond to any known particles or where the Higgs is expected to be found.

Because DZero is physically different from CDF, the whole process of modeling and subtracting has to be repeated. That's now been done for at least some of DZero's data and, so far at least, there's nothing very different from the Standard Model background apparent. The DZero team will be posting a draft of its paper on the analysis on Monday, but the figures are already available.

The real question, then, is why CDF is seeing what it is. Fortunately, with an independent analysis completed, figuring that out should be a lot easier, since it will be possible to compare values for various classes of background events. The Fermilab Director has already started the process of creating a task force, staffed by members of both teams, that will try to figure out what's different about the two analyses.

Hardcore particle physics fans may want to check out a 4pm Central Time webcast of a seminar on the DZero team's work.

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