With restart, Large Hadron Collider to search beyond Higgs boson
Maybe the "God particle" has undiscovered siblings. Maybe dark matter can be detected. After a two-year hiatus, physicists hope they might find the answers.
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In two weeks, researchers plan to restart the European particle accelerator to try to reveal more of nature's inner workings. That could include finding out whether the known Higgs boson -- sometimes referred to as the "God particle" for its role as one of the basic cogs in the machinery of the universe -- is actually a sibling in a larger Higgs boson family. It could help scientists probe the mystery known as dark matter.
Many particles throughout the universe can be explained by the Standard Model of particle physics, which describes how particles and forces interact, but doesn't explain how particles get their mass. Scientists now think the Higgs boson, discovered by LHC in 2012, gives all matter its mass.
The LHC, near Geneva, Switzerland, accelerates protons to within a sliver of the speed of light inside a huge underground circular tunnel 17 miles in circumference. Some protons travel clockwise, some counterclockwise, and the two proton beams smash into each other in the middle of mammoth experimental detectors. The resulting collisions produce a spray of extremely high-energy particles not ordinarily visible.
The LHC has been shut down for two years for maintenance and upgrades designed to help physicists explore previously uncharted terrain. LHC leaders announced the planned restart during a press conference Thursday at CERN, the European Organization for Nuclear Research, which runs the LHC.
"It could be there will be further Higgs bosons to be found," said Dave Charlton, a physicist and spokesman for Atlas, one of the four major LHC experiments. "What is the dark universe? What is the dark matter we see? Can we create it in the laboratory?"
Answers to such questions aren't likely to produce better smartphone battery life or cure cancer. But they can satisfy a basic human desire to understand the universe while training the next generation of physicists. About 3,000 students are working at the LHC.
Beyond the Standard Model
Many of those particles are well documented through the Standard Model -- but physicists know it can't explain everything.
"Ninety-five percent of the universe is unknown to us," said CERN Director General Rolf Heuer. "There must be something beyond the Standard Model."
Theoretical physicists have come up with plenty of ideas, including the "supersymmetry" approach in which the known particles are paired with so far undetected equivalents bearing fanciful names like Higgsinos, sleptons, squarks and neutralinos.
Theoreticians -- Albert Einstein, most famously -- get a lot of credit for advancing knowledge. But it takes experimental physicists to prove what's right and what's wrong, to measure the details and to uncover the surprises that spark theoreticians' next round of ideas.
For supersymmetry to be true, there have to be more Higgs bosons than just the one type found so far. One of the reasons for excitement about supersymmetry is that it offers a way to explain dark matter -- material that's more abundant than the regular matter that makes up people and planets but that so far has been detected only through its gravitational effects such as how fast stars travel within galaxies.
Moving from 8TeV to 13TeV will open up the search for more massive particles. That's because of Einstein's famous E=mc2 formula that describes how mass and energy are in effect two sides of the same coin. Particles can become energy, and vice versa.
"If you want to produce a new state of matter with a certain mass, you need to have the energy to produce it," said Tiziano Camporesi, spokesman for another LHC main experiment, CMS. "Until now we have not found things like dark matter or other evidence of new particles that go beyond the standard model. Having higher energy allows us to access a new mass regime."
To get there, CERN had to upgrade the LHC hardware. That includes replacing 18 of the 1,232 superconducting dipole magnets that accelerate the electrically charged protons fast enough to circle the ring 11,245 times per second; improving the cryogenic system that cools those magnets enough that they can function; reinforcing connections to sidestep problems that can result when warming or cooling components move; hardening electronics to withstand more high-energy radiation; and upgrading computer systems to handle more data.
Over the weekend, the LHC passed "injection" tests, in which earlier systems feed streams of protons into the main ring. Next up will be running the main LHC ring itself.
"We are very confident we can put a beam up in two weeks," Heuer said.
However, that'll just be for testing the equipment initially. Running the beams to gather the first physics data from 13TeV collisions likely will start in May.
After an explosion in 2008 delayed the LHC's first start, damaging equipment and forcing some upgrades, Heuer is cautious about moving from upgrades to tests to particle-collision operations.
"I estimate two months," Heuer said. "I prefer to take longer than to have another shutdown of five years."
The LHC should run through 2018 at the 13TeV level. Then it'll be time for another shutdown for maintenance and upgrades, and the cycle will repeat through 2035.
"It's a plan of roughly 20 years," Heuer said. "We know we need a lot of collisions."