Smooth beam delivery and fast setup enable new data on the QCD phase diagram.

In June 2025, the NA61/SHINE experiment completed its first data-taking campaign using primary oxygen ions, advancing its ongoing study of the phase structure of strongly interacting matter. Over ten days of running at 150A GeV/c in the H2 beamline, the collaboration recorded interactions of oxygen-16 nuclei with a range of fixed targets, from beryllium to lead.

Last used in 1986, the oxygen beam was delivered once more through the injector chain and extracted to the North Area towards the H2 beamline, whose commissioning for oxygen was carried out by Nikolaos Charitonidis and Bastien Rae from the Experimental Areas Group (BE-EA). Infrastructure preparations in the experimental zone, including shielding adaptations, vacuum interfaces and installation of beam instrumentation, were completed by BE-EA and other service groups including SY-BI during the very short change-over period ahead of the run.

    “The oxygen beam performed very well from the start,” says Nikolaos Charitonidis, H2 beamline physicist. “It was satisfying to see how smoothly the entire injector chain and transfer lines came together to deliver such a clean and stable beam to NA61/SHINE, a real team effort across several accelerator domains.”

In a separate short run, NA61/SHINE also recorded 4.5 million minimum-bias interactions using oxygenfragmentation products on carbon and polyethylene targets, following just three hours of setup and eight hours of data taking.

The oxygen–oxygen collisions fill an important gap in the system-size scan of the NA61/SHINE strong interaction programme. Looking ahead, the collaboration already prepared a proposal for an extended physics programme beyond LS3, including further runs with other light ion species.

Fragments of the primary oxygen beam interacting with the T2 target (Courtesy NA61/SHINE).