Summary of session 4 upgrade scenario 2

The performance target for Upgrade Scenario 2 (US2) was defined for the purposes of the RLIUP meeting as accumulating 3000 fb−1 in the years to 2035. As shown earlier in the meeting, this sets the requirement for 270 fb−1 per year of operation after LS3. The presentations in Session 4 were arranged to evaluate the performance of HLLHC given the assumed baseline upgrade path, to present the optimum beam parameters in collision and from the injectors, to evaluate whether the injectors could reach the required parameters in view of the LIU upgrades, and to then investigate possible alternative (i.e. non-baseline) ideas or possibilities for improving the performance reach of HLLHC and its injector chain. The session concluded with two talks, one on the challenges and outlook for improving the achieved physics availability of HL-LHC, and the second on the analysis of the possible issues with the baseline 25 ns bunch spacing and the estimate of the performance potential with the alternative option of 50 ns.