Fermilab is a large complex of particle accelerators 45 miles west of Chicago.
Physicists at the Fermi National Accelerator Laboratory have observed anomalous data that suggest they may have discovered a new elementary particle or a new fundamental force of nature. Or, they acknowledged Wednesday, they may have simply observed a chance statistical fluctuation in their results.
If the results are real, they could provide the first significant change in what is known as the standard model of physics in more than five decades, and researchers are holding their breaths in anticipation.
"If this thing is real, it is a new type of very heavy particle that is not one of the ones theorists have been sitting around thinking about," said physicist Michael Witherell of UC Santa Barbara. "It would be very heavy, very interesting and very fundamental. It would turn over our understanding of particle physics."
Added Harvard University physicist Lisa Randall: "If it is really something new, it would be extremely exciting."
But scientists on the Fermilab team say there is about a 1 in 1,000 chance that the results are a statistical fluke — odds far too high for them to claim a discovery.
"That's no more than what physicists tend to call an 'observation' or an 'indication,' " said Caltech physicist Harvey Newman.
For the finding to be considered real, researchers have to reduce the chances of a statistical fluke to about 1 in a million.
Researchers hope that more data compiled at Fermilab will shed light on the matter, or that the Large Hadron Collider in Geneva will be able to replicate the findings. "We will know this summer when we double the data sets and see if it is still there," said physicist Rob Roser of Fermilab, who is a spokesman for the project.
Physicists have been talking excitedly about the anomaly for at least three months, speculating on whether it is real and what it could mean. The discussion became public Wednesday when the researchers posted a paper about their findings online and presented their results at an internal seminar at Fermilab in Batavia, Ill.
The experiment was conducted in the Tevatron, a ring-shaped particle accelerator in which protons are smashed into their antimatter counterpart, antiprotons, at a rate of about 2 million times per second. The anomaly showed up in an analysis of about 10,000 collisions in which researchers expected the impacts to produce a specific signature: a heavy particle known as a W boson and two jets of quarks.
In addition to the expected results, however, about 250 of the collisions appeared to produce a different, slightly heavier particle that had not been predicted.
"The unfortunate thing is, [the heavier particle] doesn't appear in other analyses where it might also be expected to appear," said physicist Mark Kruse of Duke University, who was part of the 700-member team that obtained the results.
What the team must to do now, Roser said, is "eliminate all the mundane explanations." They have been working on that, he said, and decided it was time to go public and let others know what they had found so far.
A separate team at Fermilab, called DZero, is analyzing an independent set of data from the same type of experiment. Team members said at the seminar Wednesday that they should have those results in about two weeks.
Meanwhile, at least two theorists at the seminar said they would be presenting new papers in the next day or two offering explanations for what the new particle might be.
"My personal opinion is that it will probably be understood in ways that are not new physics," Kruse said. "But even if there is just a small chance that it is new physics, that is very exciting."
Witherell of UC Santa Barbara said he was keeping his fingers crossed. "We are all praying for a discovery," he said. "The field could use one."