In one of the apparent paradoxes that abound in particle physics, researchers had predicted that the top quark would be heavier than the proton from which it came. From their data, Fermi scientists measured the top quark's mass at about 200 times that of a proton, well within the range predicted by the theory.
At a Fermi conference late last year, participating physicists agreed that they should write a journal article analyzing their results, but wrangled over what their videotapes showed. Although they were certain they had highly significant results, they could not agree on whether they had gathered enough data to be absolutely sure they had actually created the missing particle.
At a news conference Tuesday to announce the discovery, William C. Carithers Jr., a senior staff physicist at Lawrence Berkeley Laboratory who is a visiting researcher at Fermi, said, "The evidence is too large to ignore, but too small to cry 'Eureka!' "
The researchers were anxious to stake their claim to the discovery as soon as practical but equally anxious to avoid the embarrassment of a public error. After all, a European lab had announced the discovery of the top quark previously and then retracted its claim because of mistakes in interpreting the background of vast numbers of particles.
Last week, the team submitted its 150-page manuscript to a peer-reviewed science journal called Physical Review D. A separate team of 420 researchers at Fermi is attempting to independently confirm the findings.
Fermi officials said they decided not to wait for the usual outside scientific review and make their announcement at the news conference. Word of the Fermi data was leaking out, and the group felt confident enough to declare it had found evidence of the top quark.
Some misgivings still linger.
John Peoples Jr., director of the Fermi Lab, said Tuesday, "I am persuaded that the evidence is very strong." But, he said, "there are some inconsistencies."
Carithers said that there is only a "1-in-400 chance" the scientists are wrong.
Shochet said he would like to see "two or three times" as much data "fingerprinting" of the top quark before declaring a definitive discovery, but that "this is the first time you have a serious hint of something."