Charting the Luminosity Capabilities of the CERN Large Hadron Collider with Various Nuclear Species

TL;DR

The paper addresses the problem of enhancing LHC heavy-ion performance by exploring ion species beyond Pb and predicting achievable injection intensities and luminosities with a physics-based Injector Model. By propagating beam parameters through Linac3–LEIR–PS–SPS and then simulating LHC fills with the Collider Time Evolution code, it quantifies how space charge, electron cooling, IBS, and beam-gas interactions constrain ion production. The main findings show that optimistic scenarios can reach up to about a factor $4$ increase in one-month integrated nucleon-nucleon luminosity compared to Pb baselines, while overall NN luminosity projections remain below some prior WG5 estimates, unless hardware and operational upgrades (e.g., 25 ns spacing) are implemented. The work provides guidance for ion-species selection and injector upgrades for ALICE-3 and future HL-LHC runs, and it emphasizes the need for experimental validation and targeted R&D on cooling, stripping, and vacuum performance to refine the projections.

Abstract

The Large Hadron Collider (LHC) at CERN has been instrumental in recent advances in experimental high energy physics by colliding beams of protons and heavier nuclei at unprecedented energies. The present heavy-ion programme is based mainly on colliding lead nuclei. For future ion runs, there is strong interest to achieve a significantly higher integrated nucleon-nucleon luminosity, which might be achieved through collisions of species other than Pb. In this paper, we explore the nucleon-nucleon luminosity projections in the LHC for a selection of ion species ranging from He to Xe, and including Pb as reference. Alternative beam production schemes are investigated as a way to mitigate effects such as space charge that degrade the beam quality in the LHC injectors. In the most optimistic scenarios, we find up to about a factor~4 improvement in integrated nucleon-nucleon luminosity for a typical future one-month run, with respect to the present Pb programme. We also outline a future study programme and experiments to test the assumptions and refine the simulated projections put forward in this article.

Figures (13)

• Figure 1: The Pb ion path, highlighted in dark blue, across the CERN injector chain and the LHC. Present and alternative stripper foil locations are shown, as well as the charge state evolution of Pb beams. Illustration projected on graphics from lopienska2022_cern_complex.
• Figure 2: Present Pb ion beam production scheme and bunch train structure throughout the CERN ion injector chain.
• Figure 3: Flowchart of the Injector Model.
• Figure 4: Example of measured intensity for single-bunch O$^{4+}$ pilot beams in the PS, from June 10$^{\text{th}}$ 2025.
• Figure 5: Estimated nucleons per bunch for the different scenarios, including the WG5 estimates YR_WG5_2018. He and O bars with pink frames require a $B_{\textrm{inj}}$ in the PS that presently would be too low.