The Super Proton Synchrotron (SPS) lives up to its superlative designation. It’s CERN’s second-largest accelerator and is the last link in the accelerator chain that feeds particle beams to the Large Hadron Collider (LHC). What’s more, it supplies beams to a range of non-LHC experiments that address an impressive array of topics, from precision tests of the Standard Model of particle physics to studies of the quark–gluon plasma, a state of matter believed to have existed shortly after the Big Bang.

Following hot on the heels of the restart of the Proton Synchrotron Booster and the Proton Synchrotron after the second long shutdown of CERN’s accelerator complex, the SPS and its experiments are now also back in action.

The SPS delivers particle beams to all of CERN’s North Area (NA) experiments, to the associated test beam areas, as well as to the AWAKE experiment, which investigates the use of a wakefield created by protons zipping through a plasma to accelerate charged particles, and to the HiRadMat facility, which tests materials and accelerator components in extreme conditions.

The NA experiments are an essential strand of the Laboratory’s experimental programme. NA58/COMPASS studies how quarks and gluons form composite particles such as protons and pions. NA61/SHINE investigates the quark–gluon plasma and takes particle measurements for neutrino and cosmic-ray experiments. NA62 studies rare kaon decays and searches for new heavy neutral leptons. NA63 investigates radiation processes in strong electromagnetic fields. NA64 searches for new particles that could carry a new force between visible matter and dark matter, or that could make up dark matter themselves. Last but not least, NA65, a new experiment that was approved in 2019, will take measurements of tau neutrinos for neutrino experiments and for tests of the Standard Model.

NA62 has just restarted taking data for physics studies, and the remaining experiments will start doing so in the coming weeks and months. Highlights include the start of NA65 in September and the first pilot runs in October for experiments proposed in the Physics Beyond Colliders initiative, such as AMBER (the successor of COMPASS) and NA64μ (NA64 running with beams of muons).

“It’s always a thrill to witness the restart of the experiments, as is to see the fresh data that they deliver, not least after the extensive upgrades they have undergone over the past two years,” says Johannes Bernhard, the leader of the Liaison to Experiments section at CERN. “And if the past seasons of data-taking are any indication, there will be plenty of new physics results to digest and to direct future studies.”