The Large Hadron Collider (LHC) has completed its latest physics run and officially entered Long Shutdown 3 (LS3), marking the beginning of the most extensive upgrade programme undertaken at CERN since the collider was originally built.
The shutdown will focus on maintaining, modernising and expanding CERN’s accelerator complex in preparation for the High-Luminosity Large Hadron Collider (HiLumi LHC), which is scheduled to begin operations in 2030.
The upgraded machine is expected to deliver significantly higher collision rates, allowing scientists to gather much larger datasets and perform more precise investigations into the fundamental structure of the Universe.
Although particle beams have now stopped circulating, scientific research at CERN will continue throughout Long Shutdown 3, with thousands of researchers analysing existing experimental data while engineers and technicians transform the accelerator and its detectors for the next generation of discoveries.
A remarkable legacy for the Large Hadron Collider
Since first circulating proton beams in September 2008, the Large Hadron Collider has established itself as the world’s most powerful particle accelerator and one of the most sophisticated scientific instruments ever created.
Following its first proton collisions in 2009, the collider completed three major operational periods, known as Runs 1 to 3, generating an unprecedented volume of experimental data for its international collaborations.
Its defining scientific milestone came in July 2012 with the discovery of the Higgs boson by the ATLAS and CMS experiments. The finding confirmed a key prediction of the Standard Model of particle physics and solved one of the field’s most significant outstanding questions.
The collider has continued to expand scientific understanding over the past decade, leading to the discovery of more than 85 new hadrons while providing increasingly precise measurements of known particles.
Researchers have also explored the behaviour of quark-gluon plasma, investigated the imbalance between matter and antimatter, and placed tighter limits on theories predicting entirely new particles.
Beyond fundamental physics, the project has accelerated advances in superconducting magnets, accelerator engineering, large-scale computing and international scientific collaboration.
Long Shutdown 3 will reshape CERN’s accelerator complex
Long Shutdown 3 represents far more than routine maintenance. Running until 2030, the programme will involve thousands of engineers, physicists and technical specialists from CERN and partner institutions around the world.
Work will extend across the entire accelerator chain, including major improvements to the LHC’s injector systems and extensive renovation of experimental facilities.
Among the largest projects are the consolidation of the Super Proton Synchrotron North Area, the dismantling of the former CERN Neutrinos to Gran Sasso target area, the conversion of Experimental Cavern North 3 into a high-intensity fixed-target facility, and modernisation work at the ISOLDE research facility.
Essential upgrades to electrical infrastructure, technical galleries and personnel safety systems will also be completed during the shutdown.
Detector upgrades prepare for the High-Luminosity LHC
The ATLAS and CMS detectors will undergo comprehensive upgrades to cope with the dramatically increased performance expected from the High-Luminosity LHC.
Once operational, the upgraded collider will increase its luminosity by up to ten times its original design value, producing between 140 and 200 proton-proton collisions during every bunch crossing, compared with roughly 60 during the most recent run.
To manage this enormous increase in data, both experiments will replace their trigger systems, which rapidly identify the most scientifically valuable collisions from billions of particle interactions occurring every second.
The detectors will also receive next-generation all-silicon tracking systems containing billions of readout channels, ultra-fast timing detectors capable of measuring events with precision of only a few tens of picoseconds, and upgraded calorimeters designed to operate at exceptionally high data rates.
Preparing for a new chapter in particle physics
Although the Large Hadron Collider will remain offline throughout Long Shutdown 3, the pause represents an investment in the future of high-energy physics rather than a break in scientific progress.
Researchers will continue extracting new results from the extensive datasets already collected while preparing experiments for the next phase of exploration.
The gradual restart of CERN’s accelerator complex is expected to begin in 2028, before the High-Luminosity LHC enters full operation in 2030.
With vastly improved performance and much larger datasets, the upgraded collider is expected to enable the most detailed studies yet of the Higgs boson while increasing the chances of uncovering physics beyond the Standard Model, opening a new chapter in humanity’s quest to understand the fundamental laws governing the Universe.
