Speculation suggests a long-sought particle may be at hand

By Ron Cowen

Web edition: April 29, 2011

A leaked internal document, rumors flying on blogs, and scientists in thrall. Not exactly the stuff one usually associates with experiments in elementary particle physics. But all the rules and academic niceties get thrown out the window when it’s a potential sighting of the Higgs boson.

The Higgs is the missing piece in the highly successful standard model of particle physics. The particle — or more precisely the field that the particle is associated with — would endow particles with mass, and researchers have been hunting for it for decades. Physicists also believe the discovery of the Higgs will lead to transformative insights, including new, as yet unknown physical phenomena, notes Andrew Lankford, deputy spokesperson for the ATLAS experiment at the world’s most powerful atom smasher, the Large Hadron Collider near Geneva. Whichever team finds convincing evidence of the particle will undoubtedly win a Nobel prize.

So it’s little wonder that an unvetted, leaked abstract suggesting that the ATLAS experiment might actually have found signs of the Higgs would create a clamor once it got posted on the Internet. And that’s despite the fact that no one seems to know — or at least be willing to speak publicly about — the statistical significance of the potential finding.

The abstract, written by University of Wisconsin–Madison researchers who have not answered e-mails, says that the ATLAS experiment has found more pairs of photons at an energy of 115 billion electron-volts (GeV) than expected.

That’s intriguing because many scientists think the Higgs boson may have a mass between 110 and 130 GeV. (Thanks to the equivalence of mass and energy discovered by Einstein, physicists often express mass in terms of energy.) The Higgs readily decays into other particles, and on rare occasions it would decay into a pair of photons. However, the photon excess cited in the abstract is about 30 times larger than that expected for the Higgs, the researchers note.

“The merits of searching for the Higgs decay to two photons is that this signature is more easily identified experimentally than the decay to heavy particles,” notes Lankford, who is at the University of California, Irvine.

“However, the rareness of this decay mode, particularly for a standard model Higgs, suggests that we will need to collect much more data with the LHC before we would expect to observe this decay mode.”

In an informal poll of physicists gathered for an executive board meeting of the American Physical Society in Los Angeles, “the general impression is skepticism,” says theorist Katie Freese of the University of Michigan. She adds that the data are not consistent with the standard Higgs model, nor the simplest extensions of it. “ATLAS did not vet the data so it's really too soon to tell,” she says.  

Adds Lankford: “Frankly, people should not be so excited when they don’t know the statistical significance. Statistically insignificant effects are statistically frequent, particularly when one is searching broadly for a variety of possible discoveries at a facility such as the LHC. Nonetheless ... there is a lot of pent up anticipation of the observation of the Higgs.”