Follow by Email

Popular Posts

Wednesday, 21 December 2011

Has the Higgs Been Discovered? Physicists Gear Up for Watershed Announcement

The physics buzz reached a frenzy in the past few days over the announcement that the Large Hadron Collider in Geneva is planning to release what is widely expected to be tantalizing—although not conclusive—evidence for the existence of the Higgs boson, the elementary particle hypothesized to be the origin of the mass of all matter.

Many physicists have already swung into action, swapping rumors about the contents of the announcement and proposing grand ideas about what those rumors would mean, if true. "It's impossible to be excited enough," says Gordon Kane, a theoretical physicist at the University of Michigan at Ann Arbor.

The spokespersons of the collaborations using the cathedral-size ATLAS and CMS detectors to search for the Higgs boson and other phenomena at the 27-kilometer-circumference proton accelerator of the Large Hadron Collider (LHC) are scheduled to present updates December 13 based on analyses of the data collected to date. "There won't be a discovery announcement, but it does promise to be interesting," says James Gillies, spokesperson for CERN (European Organization for Nuclear Research), which hosts the LHC.

Joe Lykken, a theoretical physicist at Fermi National Accelerator Laboratory in Batavia, Ill., and a member of the CMS collaboration, says, "Whatever happens eventually with the Higgs, I think we'll look back on this meeting and say, 'This was the beginning of something.'" (As a CMS member, Lykken says he is not yet sure himself what results ATLAS would unveil; he is bound by his collaboration's rules not to reveal what CMS has in hand.)

[Click here for a lightly edited partial transcript of the interview with Lykken that Davide Castelvecchi conducted for this story.]

The talks were announced last week; true to form, the particle physics rumor mill shifted into high gear, and by the weekend multiple anonymous sources had leaked consistent information, according to several bloggers, including Peter Woit, Lubos Motl and Philip Gibbs. Both experiments are said to have seen evidence of the long-sought Higgs, pointing to a particle mass of around 125 billion electron volts, or 125 GeV. (125 billion electron volts is roughly the mass of 125 hydrogen atoms.)* Such results would not constitute an ironclad discovery quite yet, being below the required "5 sigma," a measure of statistical reliability. But the two experiments are rumored to have seen signals of 2.5 sigma and 3.5 sigma, which together would give a strong hint. (Three sigmas would correspond to a one-in-370 chance of the finding being a statistical quirk, although in particle physics experiments it is not uncommon for 3-sigma results to vanish.)

Previous rounds of data analysis from the LHC as well as from its U.S. predecessor, Fermilab's Tevatron, had narrowed the Higgs mass range down to somewhere between 115 and 140 GeV. But the new announcement would constitute the first time that both LHC experiments had made a precise and consistent estimate of the mass.

Even before the data are out, theoretical physicists around the world are working out the possible implications. Some have pointed out that a value of 125 GeV would be good news for supersymmetry, a theory that predicts that each particle would have a heavier partner known as a superparticle (at least for particles within the framework of the Standard Model of particle physics, the currently accepted description of the subatomic world). "Most supersymmetric models put a Higgs below 140 [GeV] or so," says Matt Strassler of Rutgers University. Supersymmetry has long been a favorite candidate for extending the Standard Model, because it would answer numerous open questions, beginning with the nature of dark matter, the unseen mass that keeps galaxies rotating faster than they otherwise would.

Related Posts Plugin for WordPress, Blogger...