Final laps at the LHC

The final laps before the major overhaul: CERN's accelerator operators have just fired the starting pistol for the last run of the Large Hadron Collider (LHC). At the end of June, four years of work will begin to transform the LHC into a high-luminosity accelerator (the HiLumi LHC).

For now, let's turn our attention to the first proton collisions of the year, which were recorded by the LHC experiments on Saturday, 7 March at 15h58.

After 11 years of high-energy operation, the LHC teams have acquired such expertise that it is easy to forget the complexity of this 27-kilometre-circumference machine located 100 metres underground, equipped with more than 9000 superconducting magnets, thousands of electrical circuits and hundreds of thousands of pieces of equipment, and operating at -271 °C thanks to the world's largest cryogenic system.

"The restart of the CERN accelerator complex after the traditional winter shutdown was completed in record time," says Matteo Solfaroli Camillocci, Head of LHC Operations. "The teams have a deep understanding of the machine and are demonstrating impressive finesse in their work. It's a real team effort, and we are all looking forward to the last few months of operation."

Several types of collisions are on the menu for these four months of operation, which are starting with nine weeks of proton collisions and will be followed by three weeks of operation with lead ions. The 2026 run will end with two weeks of tests with high-intensity proton beams: bunches containing 40% more protons than the standard LHC bunches will be circulated to test the impact on the equipment. Following on from the tests carried out last autumn, the aim is to study the behaviour of high-intensity beams, which will be part of everyday operation at the HiLumi LHC, and to identify any unforeseen limitations before the shutdown begins. However, at such high intensities, the beams will contain a limited number of bunches, as the current accelerator and experiments cannot handle a higher load.

29 June will mark the start of four years of major work, during which part of the LHC will be dismantled and replaced with innovative equipment that is currently in production. The HiLumi LHC, which will start operating in 2030, will generate a significantly higher number of collisions than the current LHC, allowing physicists to study known mechanisms, such as the Higgs boson, in greater detail and to observe possible new, very rare phenomena.