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Subatomic mystery leads to standoff

Fred Ullrich / Fermilab

Two experiments at Fermilab's Tevatron collider have come to different conclusions about a scientific mystery.

Two months ago, physicists on the CDF detector team at Fermilab's Tevatron collider, just outside Chicago, reported a mysterious "bump" in the distribution of data from their proton-antiproton collisions, hinting at a non-standard twist in the Standard Model that has governed particle physics for decades.

The anomaly could have been caused by a glitch in the analysis of results from the CDF detector, or it could have been caused by a previously undetected breed of subatomic particle. If the latter turned out to be the case, that would send theorists back to the drawing board — lending weight to exotic concepts such as the existence of a "fifth force" known as technicolor. Such a finding might also suggest that the Higgs boson, the so-called "God Particle," needn't exist.

Since then, additional data from the CDF detector added to the team's confidence. They thought it was increasingly likely that something strange was really happening. But the CDF isn't the only detector at the Tevatron. There's a second detector, known as DZero, which should have seen the bump as well. In fact, the main reason why there are two detectors is so that one detector's data can be confirmed by the other. So researchers around the world anxiously awaited word from the DZero team.

Now the DZero tribe has spoken: They don't see the bump. "Nope, nothing here — sorry," New Scientist quoted DZero co-spokesperson Dmitri Denisov as saying.

The discrepancy may be due to the different computer models that the teams used to interpret what they were seeing in the masses of data from the collider. It's also possible that as more readings are added to the analysis, the margins of uncertainty will narrow down and result in more consistent conclusions. But in any case, it's way too early to write off the Standard Model, or to declare that the God (Particle) is dead.

"This is exactly how science works," DZero co-spokesperson Stefan Söldner-Rembold said in a Fermilab news release. "Independent verification of any new observation is the key principle of scientific research. At the Tevatron, we have two experiments that, by design, can check each other."

The relationship between the CDF and DZero collaborations has been compared to the rivalry between two sports teams — like the Cubs and the White Sox. But the discrepancy between the two findings "must be understood and resolved," Fermilab said. Toward that end, the lab is setting up a task force with representatives from the two teams as well as two Fermilab theorists.

Although this matchup is going into extra innings, the game won't always be tied up. Eventually, Europe's more powerful Large Hadron Collider is likely to come into play and clear up the mystery for good.

More weekend field trips on the Web:

The DZero collaboration's paper, "Study of the Dijet Invariant Mass Distribution in ppbar-->W(-->lv)+jj Final States at √(s)=1.96 TeV," has been submitted to Physical Review Letters.

The CDF team's paper, "Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in ppbar Collisions at √(s)=1.96 TeV," has been published in Physical Review Letters.

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