Particle-smashing Large Hadron Collider off to a smooth restart

Busy weekend in particle physics: Scientists spend Easter sending particles through the Large Hadron Collider

After a two-year hiatus, the giant proton-smasher that discovered the Higgs boson is back in action – and ready for bigger challenges. Scientists at the Large Hadron Collider, the most powerful particle accelerator in the world, successfully sent two beams of particles in opposite directions around its 17-mile circumference on Sunday.

Upgrades to the ring-shaped collider, located near Geneva and operated by the European Organization for Nuclear Research (CERN), will allow the beams to smash together at nearly twice the maximum energy level as before, opening uncharted territory in physics for exploration.

Scientists sent the first beam around the loop in one direction at 10:41 a.m. local time (1:41 a.m. Pacific), tracking it step by step and cheering as the beam was sent through several waystations. They sent a second beam in the opposite direction about two hours later, at 12:27 p.m.

The beams were sent at relatively low energies, and the scientists will start to ramp up the energy levels in a few days after checking the machine's systems. It will be several weeks to a couple months before the scientists start colliding particles, officials said.

Frédérick Bordry, CERN’s director for accelerators and technology, celebrated by handing out Easter eggs in the collider’s control center, according to CERN’s live blog of the event.

"Today, CERN’s heart beats once more to the rhythm of the LHC,” Rolf-Dieter Heuer, CERN’s director-general, said in a statement.  

The new-and-improved Large Hadron Collider was shut down over the last two years to undergo a host of upgrades, including replacing worn-out magnets and outfitting 10,000 electrical interconnections with metal splices that will help divert electrical current in case of a fault. At maximum energy, each beam will deliver energies of 6.5 trillion electron volts, for a particle-smashing total of up to 13 trillion electron volts – more than 60% higher than its previous energy limit of 8 trillion electron volts.

By examining the showers of particles released when the proton beams smash together, scientists were able to find evidence of the Higgs boson, a mysterious particle that had been long theorized but never detected. The discovery earned the physicists who predicted the particle’s existence a Nobel Prize in 2013.

But in some ways, the discovery of the Higgs boson offered few surprises – it fits neatly into the standard model of particle physics. The higher energies that the Large Hadron Collider will now be able to reach will allow researchers to explore mysterious phenomena that our current understanding of physics cannot explain.

Among the questions it hopes to answer: what dark matter, that strange stuff that accounts for most of the matter in the cosmos, is made of; and what happened to all of the antimatter in the universe.

“I want to see the first light in the dark universe,” Heuer said at a news briefing last month.

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