Prospects for future asymmetric collisions in the LHC

The proton-lead runs of the LHC in 2012, 2013 and 2016 provided luminosity far beyond expectations in a diversity of operating conditions and led to important new results in high-density QCD. This has permitted the scope of the future physics programme to be expanded in a recent review. Besides further high-luminosity proton-lead (p–Pb) collisions, lighter nuclei are also under consideration. A short proton-oxygen run, on the model of the 2012 p-Pb run, would be of interest for cosmic-ray physics. Collisions of protons with argon, other noble gases and nuclei of lighter metals are also discussed. We provide an overview of the operational strategies and potential performance of various options. Potential performance limits from moving beam-beam encounters at injection and various beam-loss mechanisms are evaluated in the light of our understanding of the LHC to date.