CERN switches off the LHC, begins six-year rebuild for High-Luminosity era

CERN has powered down the Large Hadron Collider after its final physics run, opening Long Shutdown 3 (LS3) — the most extensive overhaul of the accelerator complex since the LHC was built. The machine that first circulated beams in 2008 delivered the 2012 Higgs boson discovery, catalogued more than 85 new hadrons, and probed matter–antimatter asymmetry and quark–gluon plasma across three runs. Beams stop until roughly 2028, but analysis of the accumulated datasets continues throughout the shutdown.

The work between now and 2030 converts the collider, its injectors, and its detectors into the High-Luminosity LHC, which aims to raise luminosity up to tenfold over the original design for far larger datasets and sharper Higgs measurements. The scale is industrial: 1.2 km of magnets and components swapped out in the LHC alone, plus dozens of parallel projects — SPS North Area consolidation, dismantling the CNGS target area, rebuilding ECN3 as a fixed-target facility, ISOLDE renovation, and upgrades to safety, electrical, and technical systems — staffed by thousands of specialists.

ATLAS and CMS get near-total rebuilds to survive the harsher HiLumi environment, where each bunch crossing produces 140–200 collisions versus about 60 today. Both experiments replace their trigger systems to sift roughly five billion interactions per second, and add all-silicon trackers with billions of channels, timing detectors accurate to tens of picoseconds, and calorimeters running at megahertz rates. HiLumi operation is slated for 2030.