Today, May 19, 2026, marks an important milestone in the LHC project. The proton-proton collisions for the Run 3 period, that started on July 5, 2022, have officially completed. Run 3 has been a major success not only for the LHC, but also for the CMS experiment. In the years from 2010, the beginning of Run 1, until today well over half an inverse atobarn [ab-1] has been delivered by the LHC and recorded by the CMS experiment.
In the last year of Run 3 data taking LHC delivered a stunning performance, outperforming the planned data delivery by almost 10% and delivering a high quality low instantaneous luminosity run as requested by the experiment.
Towards the end of 2024 both CMS and ATLAS detectors were starting to show signs of radiation damage in their inner detectors and the closing of the Run 3 time is just in the nick of time before more serious degradation became a problem.
Before CERN is going to switch off the collider for 4 years though, there is still the much anticipated Heavy Ion run which is scheduled to start commissioning on May 23, 2026. The shutdown is scheduled to start on June 29, 2026 at 6am.
The plan for the shutdown is to upgrade the accelerator for the HiLumi LHC phase, which is “by far the largest thing CERN has done in the last 20 years” according to Mark Thomson, the reigning DG at CERN.
For the LHC experiments it will mean a ten times higher luminosity with ten time more data, which will need new detectors to deal with this new challenging regime of data delivery.