CERN's Large Hadron Collider returns to service after 3-year hiatus

Four years of physics-data taking are set to begin this summer at the LHC, marking the third run of the collider.

A general view of the Large Hadron Collider (LHC) experiment is seen during a media visit at the Organization for Nuclear Research (CERN) in the French village of Saint-Genis-Pouilly near Geneva in Switzerland, July 23, 2014 (photo credit: REUTERS/PIERRE ALBOUY)
A general view of the Large Hadron Collider (LHC) experiment is seen during a media visit at the Organization for Nuclear Research (CERN) in the French village of Saint-Genis-Pouilly near Geneva in Switzerland, July 23, 2014
(photo credit: REUTERS/PIERRE ALBOUY)

The Large Hadron Collider (LHC) at CERN was restarted on Friday after being turned off for over three years for maintenance, consolidation and upgrade work.

Two beams of protons circulated in opposite directions around the LHC at 1:16 p.m. Israel time on Friday.

“These beams circulated at injection energy and contained a relatively small number of protons. High-intensity, high-energy collisions are a couple of months away,” said the head of CERN’s beams department, Rhodri Jones, in a press statement. “But first beams represent the successful restart of the accelerator after all the hard work of the long shutdown.”

Four years of physics data-taking are set to begin this summer at the LHC, marking the third run of the collider. Until then, experts at the collider will work to recommission the machine and safely ramp up the energy and intensity of the beams before collisions for experiments will take place at a record energy of 13.6 trillion electronvolts.

The new run will allow the international teams of physicists who operate at CERN and across the world to study the Higgs boson in greater detail and conduct the most stringent tests ever conducted on the Standard Model of particle physics, the current central theory of how particle physics works.

 A man works in the European Organization for Nuclear Research (CERN) Control Centre in Meyrin near Geneva, Switzerland, April 13, 2022. (credit: REUTERS/PIERRE ALBOUY) A man works in the European Organization for Nuclear Research (CERN) Control Centre in Meyrin near Geneva, Switzerland, April 13, 2022. (credit: REUTERS/PIERRE ALBOUY)

This July marks ten years since the Higgs boson was discovered at CERN.

Not only will the energy of the collisions be higher than the past runs, but the number of collisions will also significantly increase as well. The ATLAS and CMS experiments at CERN are expected to receive more collisions than in the previous two runs combined. The LHCb, meanwhile, will see its collision count increase threefold.

ALICE, a specialized detector for studying heavy-ion collisions, is expected to see a fifty times increase in the total number of recorded ion collisions, according to CERN.

Two new experiments will also begin operations in the latest run: FASER and [email protected], which will both look for physics beyond the Standard Model; special proton–helium collisions to measure how often the antimatter counterparts of protons are produced in these collisions; and collisions involving oxygen ions to help improve knowledge about cosmic-ray physics and quark-gluon plasma, a state of matter that existed shortly after the Big Bang.

“The machines and facilities underwent major upgrades during the second long shutdown of CERN’s accelerator complex,” said CERN’s director for Accelerators and Technology, Mike Lamont. “The LHC itself has undergone an extensive consolidation programme and will now operate at an even higher energy and, thanks to major improvements in the injector complex, it will deliver significantly more data to the upgraded LHC experiments.”

The LHC is the world's largest and most powerful particle accelerator, measuring 27-kilometers long. Two high-energy particle beams travel at close to the speed of light inside the accelerator until they collide, forming new particles and allowing physicists to study particles that are unstable and cannot be directly observed.

Additionally, on Friday, construction began on the new CERN Data Center in Prévessin which will come online in the final quarter of 2023. The new, energy-efficient facility will help meet the computing needs created by the upgrade program at the LHC set to be completed in 2029 when the High-Luminosity LHC (HL-LHC) begins operations.

The HL-LHC is expected to again significantly increase the number of collisions at the collider. For example, while the LHC produced about three million Higgs bosons per year, the HL-LHC is expected to produce at least 15 million.

The total computing capacity which will be required by the experiments run once the HL-LHC comes online is expected to be ten times greater than it is today.