The start of the LS3 in the LHC
Jean-Philippe Tock for the LS3 Coordination team
On 28-29 May, more than 150 physicists, engineers, and technicians from all groups involved in LS3 accepted the mission to perform the LS3 check-up (https://indico.cern.ch/event/1654765/), (See picture) with the objective to confirm the readiness of all projects, equipment and support groups for the LS3. It followed previous reviews held in 2024 and 2025. It has identified some points to be followed but there is no obstacle to start the LS3 interventions in the LHC on 29th June early in the morning.
For the injectors, the transition from operation mode to LS3 will take place on 31st August. Note that the dismantling of the CNGS Target Area and the replacement of the ISOLDE beam dumps, two LS3 projects are already well underway since 2025, June and December respectively.
The third Long Shutdown (LS3) marks a defining stage in CERN’s roadmap and represents one of the most ambitious intervention programmes ever undertaken across the accelerator complex. More than a routine maintenance period, LS3 is designed to prepare CERN’s accelerator complex for the next era of high-energy physics and to unlock the full scientific potential of the Large Hadron Collider thanks to the HL-LHC project and the upgrade of the LHC detectors, especially ATLAS and CMS.
A central objective of LS3 is to enable the installation and commissioning of the HL-LHC, a major upgrade that will significantly increase the collider’s luminosity and expand opportunities for discovery. At the same time, the shutdown includes substantial upgrades to the ATLAS and CMS experiments, ensuring they are fully equipped to exploit the increased data volumes expected during Run 4.
Beyond this, LS3 encompasses an extensive programme of consolidation, maintenance, and technical enhancements across the entire accelerator complex. The scope and diversity of the work make it the largest programme undertaken since the original installation of the LHC, exceeding the scale of both LS1 and LS2.
Delivering such a complex transformation requires close coordination across CERN’s sectors, departments, and project teams. Success depends on aligning numerous activities, managing interdependencies, and maintaining a shared focus on long-term objectives.
LS3 also represents a strategic opportunity to boost operational performance, strengthen the reliability of CERN’s infrastructure, and ensure the long-term availability of its facilities for future scientific research.
It’s you, your energy, and your commitment that will make this adventure—the LS3—meaningful. There will be obstacles, but together, we’ll overcome them with determination and teamwork.
Today, we stand at the beginning of a four-year endeavour for the LHC—an effort already underway in some facilities and already providing valuable lessons. Together, we will embark on this journey: LS3. It will be a period filled with challenges, learning opportunities, and unforgettable moments.