What Is Long Shutdown 3 at CERN and What Work Is Happening During It?

Long Shutdown 3 (LS3) is the major maintenance and upgrade phase that CERN's accelerator complex and experiment facilities are undergoing as of mid-2026. Its central goal is to transform the Large Hadron Collider (LHC) into the High-Luminosity LHC (HiLumi LHC), while most other accelerators and experimental facilities are also being upgraded at the same time. The work involves thousands of experts from many different disciplines, and CERN provides a progress-tracking page on home.cern for those who want to follow it.

What LS3 is meant to achieve

The headline objective is the HiLumi LHC. According to CERN, the upgrade will increase the number of particle collisions — a quantity called "luminosity" — by a factor of ten. That vastly increases the volume of physics data available to researchers and lets physicists study the behaviour of the Higgs boson and other elementary particles with unprecedented precision, raising the potential for discoveries after 2030.

Two things are worth separating here:

• Luminosity vs. energy. The upgrade multiplies collision rate, not the beam energy of the machine. More collisions means more rare events collected over the same running time.
• Timeline. CERN frames the payoff as discoveries "after 2030," so LS3 is a preparation phase, not a period of new physics results from the LHC itself.

What work is happening

The page evidence describes LS3 as work "centred on" the LHC-to-HiLumi transformation, with most other accelerators and experimental facilities being upgraded as well. It does not itemise individual components, so the safe summary is:

For specifics on particular magnets, cryogenics, detectors or civil engineering, the progress-tracking page is the intended entry point rather than a static description.

How to follow progress

CERN's own route is the "Follow the progress" link on the LS3 section of home.cern. Use it if you want current status rather than a fixed overview; the page evidence shows the site's news listings can return no posts under some category or date filters, so if a filtered view looks empty, widen the category or date range instead of assuming nothing is happening.

Context: what comes after

LS3 sits between the LHC's current run and two longer-term projects CERN describes on the same page:

• HiLumi LHC — marked "in preparation," the upgraded machine described above.
• Future Circular Collider — presented as a possible Europe's next-generation particle collider, framed as "looking to the future."

Practical takeaways

• If you encountered "Long Shutdown 3" in news coverage, it refers to maintenance and upgrade work, not an accident or premature end of the LHC programme.
• Expect a gap in new LHC collision data during this phase; results in the meantime come from analysis of existing data and from other facilities as they return.
• For anything time-sensitive — schedules, milestones, restart dates — check the CERN progress page directly, since the overview text describes the phase rather than dated milestones.