June 29, 2012 at 11:24 PM ET
Has the Higgs boson finally been detected? It's almost gotten to the point that if a discovery of some sort doesn't come out of next week's update on the multibillion-dollar subatomic search, it'll be a big surprise. But how far will the announcement go, and what will it mean for the future of physics?
To refresh your memory, the Higgs boson is the only fundamental subatomic particle predicted by theory but not yet detected. It's thought to play a role in endowing some particles, such as the W and Z boson, with mass ... while leaving other particles, such as the photon, massless. The Higgs mechanism, proposed by British physicist Peter Higgs and others in the 1960s, could have played a role in electroweak symmetry breaking, which was a key event in the rise of the universe as we know it.
The Higgs boson is so key to the current understanding of fundamental physics that Nobel-winning scientist Leon Lederman nicknamed it the "God Particle" — a term that has been making other physicists wince ever since. Another religion-tinged cliche would be to call it the "holy grail of particle physics," as CERN physicist John Ellis has. He says finding the Higgs is a key goal for the $10 billion Large Hadron Collider.
"That's one thing that we're really looking forward to with the LHC," Ellis told me five years ago. "In fact, back when we persuaded the politicians to stump up the money to build the thing, that's probably what we told them."
Last December, the teams reported that they saw "tantalizing hints" of the Higgs' existence at a mass of around 125 billion electron volts, or 125 GeV. But the confidence in those results was not yet high enough to claim a discovery. Now the teams behind the collider's CMS and ATLAS experiments have collected higher piles of data, at higher energy levels, sparking higher expectations.
The 5-sigma fetish
When physicists talk about their confidence, they talk in terms of statistical "sigma" levels. The higher the sigma, the less likely that the results are just a fluke. In particle physics, 3 sigma constitutes strong evidence, but it takes 5 sigma to accept the results as a discovery. At the 5-sigma level, statisticians say there's roughly one chance out of 3 million that you're leaping to the wrong conclusion, as opposed to a 1-in-1,000 chance at the 3-sigma level. That distinction makes a big difference when you're sifting through billions upon billions of proton-on-proton collision reports.
Last year, the best that the LHC teams could do was 3.6 sigma for ATLAS, and 2.6 for CMS. Now physicists are looking for a 5.
For three weeks, the teams have been running the numbers on their experimental results in secret, so as to avoid any chance that one analysis will influence the other. Their results are to be announced during a presentation at the CERN nuclear research center in Geneva, which will be webcast starting at 9 a.m. CEST (3 a.m. ET) on July 4. Although no official word has leaked out, the unofficial word is that someone looking for a discovery could get to the magic number.
"Reports from the experiments indicate that at least one of them, if not both, will reach the 5 sigma level of significance for the Higgs signal, when they combine 2011 and 2012 data and the most sensitive channel. So, this will definitely be the long-awaited Higgs discovery announcement, and party time for HEP [high-energy physics] physicists," Columbia mathematician Peter Woit wrote on his Not Even Wrong blog a week ago.
Since then, other physicist-bloggers have been fine-tuning the expectations. Here's a selection:
Hedging on the Higgs
What Strassler and Gibbs are saying is important: Technically speaking, CERN is unlikely to announce that the Higgs boson has been definitively discovered. It's more likely that physicists will talk about a new particle that has a signature consistent with the Higgs but has to be investigated further.
CERN hinted at that approach last week in the news release announcing Wednesday's webcast. "It's a bit like spotting a familiar face from afar," said the center's director general, Rolf Heuer. "Sometimes you need closer inspection to find out whether it's really your best friend, or actually your best friend's twin."
Gigi Rolandi, a senior research physicist at CERN, used a similar analogy in a video released this week, referring to crops of corn (which he calls maize, as most Europeans do), wheat (which he calls corn) and poppy flowers. Some particles are as easy to spot as a red poppy in a wheat field, he said. But not the Higgs. "The search for the Higgs is more similar to looking for a single plant of maize among many, many corn plants, than looking for a poppy among the corn," he said.
We'll get a foretaste of Wednesday's proceedings on Monday, when Fermilab is due to provide its final update on the Higgs boson search, based on the full set of data from the now-closed Tevatron. Will Fermilab try to steal some of CERN's thunder, at least for a couple of days? Stay tuned....
Update for 12:05 p.m. ET June 30: Some commenters are asking whether there are practical applications for the discoveries that could be made at the Large Hadron Collider. I addressed that question in a story I wrote four years ago, headlined "Discovery or Doom? Collider Stirs Debate." Please check out the article, as well as the Flash interactive on "Nightmares and Dreams" at the LHC.
Update for 6 p.m. ET July 1: To watch streaming video of the Fermilab Higgs update at 9 a.m. CT (10 a.m. ET) Monday, click through to this Web link.
The buzz leading uo to H-Hour is getting even louder, as expected. The Daily Mail reports that some of the theorists behind the Higgs boson concept have been invited to the CERN briefing on Wednesday, which some observers see as another sign that something definitive will be announced. Also, Reuters' Robert Evans keeps the buzz humming in a dispatch published today.
Previous episodes in the Higgs hunt:
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.