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After the Higgs, LHC Rounds Up the Unusual Suspects in Particle Physics

Physicists say that within the next few months, the Large Hadron Collider could produce exotic phenomena such as dark matter particles. Or not.
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SAN JOSE, Calif. — Supersymmetry and dark matter, neutralinos, gravitinos and gluinos ... you can expect exotic topics like these to be spinning around as the Large Hadron Collider ramps up to smash subatomic particles again over the next couple of months.

Physicists say the first hints of unconventional physics, such as evidence for the existence of those weird-sounding gluinos, could emerge within the next few months. Or not.

It's been almost three years since scientists at Europe's CERN particle physics lab announced that the world's most powerful collider had found the Higgs boson, a mysterious particle whose existence was predicted almost a half-century earlier. It's been two years since the LHC was shut down for repairs and upgrades. Now thousands of physicists are getting ready to send beams of protons through the machine for the first time since 2013.

"The beam is knocking at the door," Frederick Bordry, CERN's director for accelerators and technology, said Saturday during a preview of the LHC's second experimental run at the annual meeting of the American Association for the Advancement of Science, here in San Jose.

Bordry said the LHC's supercooled magnets are being prepared for the first proton beams to start circulating around the end of March. Scientific observations would begin after a two-month conditioning period, or by the end of May, he said.

"Don't kill me if we are taking three or four days more," he joked.

LHC gets an energy boost

It has taken decades to plan and build the $10 billion Large Hadron Collider and its four main detectors, housed in tunnels that run 300 feet (100 meters) beneath the countryside at the French-Swiss border. Now Bordry and others at CERN have mapped out a schedule of experimental runs and maintenance periods to keep the LHC on the frontier of physics until at least 2035.

The upcoming run is scheduled to last until 2017. During that time, the LHC will ramp up to smash protons together at 60 percent higher energies than it did at the end of its initial run: 13 trillion electron volts, or 13 TeV, as opposed to 8 TeV. Moreover, the beam luminosity will be three times higher.

That means the collider's detectors should be detecting Higgs bosons — particles that are associated with the process that imparts mass to other subatomic particles — at five times the frequency, said Beate Heinemann, a physicist at the University of California at Berkeley and the Berkeley Lab who's part of the LHC's ATLAS experimental group.

Heinemann said the boost in the LHC's capabilities should also improve scientists' chances of detecting gluinos, a theoretical particle predicted by supersymmetry theory, by a factor of 60.

Hints of weirdness

Heinemann and her colleagues said the collider's initial three-year run has already pointed to some apparent discrepancies with the Standard Model, the theory that currently holds sway in particle physics. However, those discrepancies have not yet shown up at a confidence level that would persuade scientists that something weird was really going on.

If the weirdness is real, the LHC could provide evidence for it during the upcoming run, perhaps as soon as August or September, Heinemann told reporters.

The new phenomena could take the form of supersymmetric particles, as-yet-undetected bits of matter that would add an elegant twist to the Standard Model. One such particle could be a gluino, the supersymmetric partner of a known particle called the gluon.

Other hypothesized supersymmetric particles include neutralinos, which could account for the universe's mysterious dark matter; and gravitinos, which could help explain dark matter as well as some of the mysteries surrounding gravity. The discrepancies also could be caused by a new breed of fourth-generation quark, Heinemann said.

Image: Supersymmetry particles
Supersymmetry theory, or SUSY, suggests that each fundamental subatomic particle we've detected to date has a yet-to-be-discovered partner with complementary characteristics. The red box highlights the gluino, a particle that physicists believe could be detected at the Large Hadron Collider. If it exists, that is.CERN / CMS Collaboration

However, there's also a chance that the apparent discrepancies are nothing more than statistical glitches. That's what happened a couple of years ago, when physicists saw hints pointing to the existence of a second kind of Higgs boson — only to watch those hints fade away as more readings were taken.

"When you put a thousand physicists in a room to do data analysis, and each one of them makes 100 or 1,000 data plots, you're likely to get statistical anomalies now and then — just like monkeys in the room typing out Shakespeare plays. Things happen," said UCLA physicist Jay Hauser, a member of the LHC's CMS collaboration.

He said the data anomalies will provide a focus for future observations.

"If it's statistics, they'll probably go away or diminish," Hauser said. "If it's real and interesting, then the effect will grow, and we get really excited."

Fermilab physicist Don Lincoln discussed the upcoming restart of the Large Hadron Collider — and the discoveries that may lie ahead — with NBC News' Alan Boyle earlier this month on "Virtually Speaking Science." Read the pre-show interview, and listen to the hourlong podcast via BlogTalkRadio or iTunes.