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CERN particle accelerator restarted

The world's biggest and most powerful atom smasher is once again circulating beams of protons after a shutdown of more than three years for upgrades.

Inside CERN's Large Hadron Collider
Inside CERN's Large Hadron Collider (AN/J. Heilprin)

GENEVA (AN) — The world's biggest and most powerful atom smasher is once again circulating beams of protons after a shutdown of more than three years to allow for maintenance, consolidation and upgrades, the European Organization for Nuclear Research said on Friday.

The Large Hadron Collider restarted in the early afternoon with two beams containing a relatively small number of protons circulating in opposite directions around its 27-kilometer ring at their injection energy of 450 billion electronvolts (450 GeV), CERN reported. The aim of increasing the LHC's energy is to increase the number of proton collisions for experiments, which boosts the probability of more discoveries about the universe’s fundamental properties.

“High-intensity, high-energy collisions are a couple of months away,” said Rhodri Jones, head of the beams department at the international organization known by its French acronym CERN. “But first beams represent the successful restart of the accelerator after all the hard work of the long shutdown.”

As part of the upgrades, CERN connected several tunnels 100 meters underground and made renovations to some surface buildings at its complex along the Swiss-French border. The LHC has a limited life-span and is sometimes shut down for repairs or upgrades.

CERN officials said pilot beams briefly circulated in the LHC in October 2021, but the beams of protons sent around on Friday marked the beginning of preparations for four years of physics-data taking, which is expected to start this summer.

A closer look at the Higgs boson

The LHC will gradually be recommissioned to safely ramp up the energy and intensity of beams before delivering collisions to experiments at a record energy of 13.6 trillion electronvolts (13.6 TeV). It is now expected to operate in a high-luminosity mode by the start of 2028.

Luminosity refers to the number of collisions among sub-atomic particles. The higher the luminosity, the more data become available. The upgrades will increase the number of proton collisions for experiments.

In 2012, CERN announced the discovery of a “missing cornerstone of physics” when it detected the Higgs boson, a new subatomic particle that had been predicted earlier by scientists almost a half-century before and helps explain why all matter has mass.

During this third phase run of the LHC, called Run 3, international teams of physicists expect to study the Higgs boson more closely and further test how physicists believe the universe was created, CERN officials said.

Among the new experiments planned are special proton–helium collisions to measure how often antimatter counterparts of protons are produced and other collisions with oxygen ions to look at cosmic-ray physics and the quark–gluon plasma.