U.S. particle physicists say they may have observed a new elementary particle or force of nature but admit it may be merely a statistical aberration.

Researchers at the Fermi National Accelerator Laboratory in Illinois said if the results are confirmed, they could require the first significant change in what is known as the standard model of physics in more than five decades, the Los Angeles Times reported Thursday.

"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," physicist Michael Witherell of UC Santa Barbara told the Times.

"It would be very heavy, very interesting and very fundamental. It would turn over our understanding of particle physics."

However, the Fermilab researchers say there is about a 1 in 1,000 chance the results a due to a random statistical fluctuation, so they are not yet claiming a discovery.

"That's no more than what physicists tend to call an 'observation' or an 'indication,'" Caltech physicist Harvey Newman said.

For the finding to be considered real, further study would have to reduce the chances of a statistical fluke to about 1 in a million, scientists said.

"We will know this summer when we double the data sets and see if it is still there," Fermilab physicist Rob Roser, spokesman for the project, said.