July 25, 2011 at 12:28 AM ET
The latest results from Europe's Large Hadron Collider have raised hopes among particle physicists that the elusive Higgs boson — also known as the "God Particle" — may be coming to light at last.
Sure, we've heard that before: Rumors about a possible detection at Fermilab's Tevatron, a particle collider near Chicago, have been circulating since last year, and just in the past few months there's been a rise and fall in expectations that the Higgs would turn up in the Tevatron's data.
Now the potential signature of the Higgs boson has turned up in an avalanche of data from both of the Higgs-hunting detectors at the Large Hadron Collider. The signature is not yet clear enough to constitute a discovery, but it suggests that the $10 billion particle collider, arguably the biggest and costliest science experiment on Earth, just might be on the right track.
"We cannot say anything today, but clearly it's intriguing," Fabiola Gianotti, spokeswoman for the science team behind the LHC's ATLAS detector, told The Guardian. Similarly intriguing results were reported by the team for the other detector, the Compact Muon Solenoid or CMS.
The two sets of findings were reported independently on Friday at the Europhysics Conference on High-Energy Physics in Grenoble, France, one of the world's biggest particle-physics forums. The ATLAS and CMS teams have been sorting through billions upon billions of data points from proton collisions at the LHC, looking for the statistical signs that suggest Higgs bosons are being shaken free for tiny fractions of a second.
The newly reported analyses suggest that the type of Higgs boson predicted by Standard Model of particle physics could be turning up around the mass-energy level of 140 billion electron volts, or 140 GeV. That's about the same level reported by one of the Tevatron's research teams.
When it comes to statistical significance, the results are not yet solid enough to constitute a confirmed discovery. But the fact that multiple detectors at two colliders are coming up with similar "bumps" in their data is nevertheless generating excitement.
"No reputable scientist is going to tell you anything more than 'this is very, very interesting and we'll keep an eye on it.' But it is indeed very, very interesting," Fermilab's Donald Lincoln, a member of the CMS collaboration at the LHC as well as the Tevatron's DZero collaboration, told me in an email.
Some are not yet convinced. The University of Padua's Tommaso Dorigo, who is part of the CMS team as well as the Tevatron's CDF team, said he doesn't see "anything compelling" in regards to the Higgs' potential detection. Rather, he sees the results as more significant for identifying energy levels where the Standard Model Higgs almost certainly won't be found. But everyone who's in the know pretty much agrees that it won't be long before physicists can say definitively whether the kind of Higgs particle they've been looking for does or does not exist.
"While I'd hate to predict an exact date, it's pretty clear from the performance seen thus and the expected near future that the Higgs will be found or ruled out on a time scale of months or perhaps a year," said Lincoln, author of the book "The Quantum Frontier."
What's so big about the Higgs?
Detecting the Higgs boson would be a big deal: It's the main reason why the Large Hadron Collider was built in the first place.
The LHC circulates protons around a 17-mile-round (27-kilometer-round) underground tunnel on the French-Swiss border to nearly the speed of light, and smashes them together within the giant ATLAS and LHC detectors as well as other special-purpose detectors distributed around the collider ring.
The more exotic products of those collisions almost instantly decay into more common subatomic particles, but by analyzing the distributions, directions and velocities of those particles, physicists can theoretically untangle big mysteries ranging from the origins of the universe to the nature of dark matter and the potential existence of extra dimensions in the cosmos.
The Higgs boson, and its associated field, is one of those big mysteries. Back in the 1960s, British physicist Peter Higgs and others proposed the boson's existence as the answer to a theoretical question about the nature of particle mass.
It's long been known that some particles (such as the quarks and leptons that make up matter) have mass, while others (such as the photon) are massless. But there was no solid explanation for the difference.
Higgs and his colleagues suggested that a type of field — analogous to a magnetic field — affected different particles in different ways, imparting mass to some particles but not to others.
In particle physics, fields are associated with force-carrying particles, which are put in a category of particles known as bosons. The particle associated with the Higgs field came to be known as the Higgs boson. Nobel-winning physicist Leon Lederman nicknamed it the "God Particle" because it played a central but subtle role in our conception of the cosmos. (Higgs and many other physicists hate the nickname.)
If the Higgs boson is found, and if it behaves in a manner consistent with the Standard Model, that would serve as an exciting validation of our current view of the structure of the cosmos. If the Higgs isn't found, or if it behaves in a non-standard way, that could be even more exciting. Physicists would have to go back to the drawing board and modify their explanation for the workings of the universe.
It's hard to predict how going back to the drawing board might affect the scientific world, or our everyday lives ... but the last time this sort of thing happened was a little more than a century ago, when quantum mechanics and relativity had to be invented to explain phenomena that just seemed weird to 19th-century physicists. These scientific paradigm shifts opened the way to innovations ranging from atom bombs and nuclear power to microwave ovens and lasers. So who knows where post-Standard Model physics might lead?
The details of discovery
Here's one more important thing to keep in mind: Discovering the Higgs won't be like discovering a new continent. Lots of numbers have to be crunched, and lots of statistics have to be analyzed to tease out the evidence for a previously undetected particle.
"It's much more like walking toward people in the fog, and waiting for the moment when you recognize the person you're looking for," Lincoln told me. The process that's playing out right now is probably the way discoveries work in 21st-century physics: First there are hints that something interesting might be going on, then more data are deciphered to confirm a discovery, and then physicists finally figure out how that knowledge can be put to use.
With that in mind, here's how Lincoln explains the slight "bump" seen in the newly reported data from the Compact Muon Solenoid:
"Take a look at the image above. There are a couple of important things. First, there's a horizontal red line. This is the Standard Model. If the black or blue line goes below the red line, the Standard Model version of the Higgs boson is ruled out for that mass. So, except for some wiggles, the Standard Model Higgs is ruled out from about 150 billion electron volts, or 150 GeV, to 460 or so.
"The thing that is getting people a little excited is the second feature. The dashed black line is how well we expect to do if the Standard Model is right, but the Higgs boson doesn't exist. When the blue and black lines start to drift away from the dashed black line, it means that we expect we can rule out more than we did. For instance, in this case, we expected to be able to rule out from about 125 GeV and up. But since the blue and black lines don't dip below the red lines until 145 or 150 or so, this could mean that we have more events than physicists would expect to see from the Standard Model without the Higgs. So that could mean there are some Higgs events floating around. The difference is biggest around 145 GeV or so.
"Now we get a reality check. The green and yellow bands indicate our uncertainty in our expectations. So we see that the black and blue lines are at the edge of our uncertainty. Further, even in the region we are excluding (near 160 GeV), there is an excess (observed above expectation).
"This means (to me at least, and at this point it's all a matter of judgment) that it could be that the discrepancy reflects an imperfect understanding of the detector and algorithms.
"Still, all of the experiments sees an excess at some level, suggesting that either our theory has been implemented incorrectly or maybe something is going on. No reputable scientist is going to tell you anything more than 'this is very, very interesting and we'll keep an eye on it.' But it is indeed very, very, interesting.
"At the Lepton/Photon conference to be held in a month in Mumbai, the ATLAS and CMS experiments will hopefully combine their results, effectively doubling the amount of beam being used."
Now that you've gotten the hang of reading the data, here's the corresponding chart from the ATLAS detector.
The bracketed areas indicate mass-energy regions where the Standard Model Higgs has been excluded: 155 to 190 GeV and 295 to 450 GeV.
If you look ever so closely at the chart, you'll notice a slight elevation of the black line above the yellow zone of uncertainty at about 140 GeV, the same area where the CMS team detected the potential signature of a Standard Model Higgs boson:
The bottom line? Something interesting may be going on in the world of physics, although there's still a chance that results or theories are being misinterpreted. Within the next year or so, we should know whether we're in the midst of a cosmic discovery. Stay tuned ...
Update for 6:05 p.m. ET July 25: The director general of the organization that hosts the LHC — known as the European Organization for Nuclear Research or CERN — says he expects the question of the Higgs boson's existence to be solved by the end of 2012. "I would say we can settle the question, the Shakespearean question — 'to be or not to be' — end of next year," Director General Rolf Heuer told reporters at the Grenoble conference.
Correction for 11:10 a.m. ET July 26: I've corrected the name of the ATLAS collaboration's spokeswoman, which I scrambled up as I was writing this item. Mi dispiace!
More about particle physics and the LHC:
For more about the findings presented in Grenoble:
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