If all goes well, in a few years, every news outlet in the world will run an image like this one right below a photo of researchers popping champagne bottles. It's a visualization of data from an experiment that is actively searching for the Higgs boson, the proposed source of all mass in the universe. In fact, it could *be* the signal from a Higgs boson.
Later this summer, researchers may finally begin to flush out some of the remaining hiding places for the Higgs using data from the Tevatron, the world's most powerful particle accelerator, located in Batavia, Illinois, at the Fermi National Accelerator Laboratory. That's the take-home message of a talk here at the American Physical Society meeting in St. Louis that summarized the state of the Higgs hunt.
The Tevatron smashes protons and antiprotons together to generate particles that haven't existed since the big bang. Those particles quickly explode into lighter, more stable kin in certain combinations--which is what researchers look for in their detectors (and depicted in the image above). By far their most challenging quarry has been the Higgs, the last missing piece of the standard model of particle physics, thought to give mass to its fellow particles by acting sort of like a molasses through which they all have to plow.
You may have heard of the Large Hadron Collider (LHC)
, the whopping big successor to the Tevatron, set to spark up later this year near Geneva. If the Higgs exists, everyone is confident that the LHC will find it. But Tevatron researchers would be ecstatic if they could steal a bit of the LHC's thunder with some last-minute evidence for the giver-of-mass.
Finding the Higgs would be a lot easier if researchers knew exactly how much it ought to weigh, but the standard model doesn't tell them that. Instead they've had to rely on indirect clues. (Note: Physicists refer to the mass of a particle in terms of the energy locked up in that particle--according to good old E=mc2
--which is also the amount of energy a particle collision must contain to produce that particle.)
Experiments at the Tevatron have precisely measured the masses of the top quark and some other particles believed to interact with the Higgs, which, combined with other data, imply that the mass of the God particle very likely lies between 114 and 160 billion (giga) electron volts (GeV). (One GeV
is about the mass-energy of a proton at rest.)
The Tevatron can hit those high-energy notes. However, it would only generate maybe a few tens of Higgs particles before the machine closes for business at the end of next year or the year after, according to particle physicist Brian Winer of Ohio State University, who gave the talk about the Higgs search.
The big challenge, he explained, is being able to sort those handfuls of events from tons of similar-looking particle bursts that happen much more frequently. The Tevatron data shown above, for example, was obtained three years ago and has the characteristics of a Higgs but is four times more likely to be the result of something more mundane, Winer said.
Whether the Tevatron can potentially detect the Higgs in a certain mass range depends in part on how many collisions its instruments have recorded at the corresponding energy. Winer said that right now, it looks like experiments should begin to scour for the Higgs at 160 GeV by this summer. Either they will give the LHC something tantalizing to follow up on, or that will be one less mass that the Higgs could have.