Future of light ions at LHC: Run 4 and beyond

In recent years, upgrades across CERN’s injector complex and the Large Hadron Collider (LHC) have significantly enhanced the performance in the ion program with Pb beams, reaching new records. While heavy-ion operation will continue in Run 4 (2030–2033), the objectives for Run 5 (currently foreseen to start in 2036) would benefit from significantly higher nucleon–nucleon luminosity. Since further major gains with the present Pb–Pb configuration are not obvious, this work explores the use of lighter ion species and alternative production schemes. A numerical computational program that accounts for realistic limitations in the injectors, is used together with beam-tracking simulations in the LHC, to estimate the achievable luminosity in a typical one-month run. Results indicate that, under optimistic assumptions, the lightest studied species (oxygen), could yield up to a factor 4 increase compared with the baseline Pb–Pb case, while larger collision systems provide smaller improvements. These projections however, rely on untested concepts and require further validation through injector studies and hardware upgrades. The findings of this work underline the potential of light-ion operation to expand the discovery reach of future LHC experiments beyond Run 4.