The performance ramp-up of the LHC after LS3 foresees a smooth ramp-up of the effective pile-up density for the nominal case, with a nominal bunch intensity reached after two years (i.e. as of 2029: 1.7 × 10¹¹ in 2027 and 2028 is a placeholder for the bunch intensity reached in Run3 in LHC, whose target will be better defined next year). The crab cavities and hollow electron lenses will be operated and commissioned at the start of Run4 only during Machine Development periods (i.e. they will be used in regular operation as of 2029 and if there are issues at higher intensity, they can be switched off transparently). The nominal 𝛽* will be reached only after LS4, which is the first year of operation with ultimate performance (see Table 1). The values of 𝛽* at the start of the levelling process provide an initial luminosity of 2.5 × 10³⁴ cm⁻² s⁻¹ as requested by the cryogenics team. The final 𝛽* will not be reached during Run4 as: firstly, the accuracy class 0 for the power converters of the main inner triplet magnets and class 0.5 for the main dipoles have to be proven in operation and secondly, the MS10 sextupole in Q10 of IR1/5 will not have been installed yet, which will lead to a reduced control of chromaticity. The MS10 sextupole is and remains in the HL-LHC baseline, helping to correct chromatic aberrations induced by the triplet and improving the beam lifetime especially at low 𝛽*. However, the impact of not installing the MS10 sextupole has been investigated in detail and it was decided not to install it during LS3, to unload the magnet group activities, as the MS10 impact is small for 𝛽* values higher than 20 cm. For 𝛽* values lower than 20 cm (to be operationally used as of Run5), the MS10 impact is expected to be higher, requiring an MS10 installation during LS4.

Assuming a total of 2090 days of proton physics, the evolutions of the peak and integrated luminosities are shown in Figure 1 for the nominal performance (where the integrated luminosity goal is predicted to be exceeded by 20%) and in Figure 2 for the ultimate case (where the goal is predicted to be exceeded by 4%). The presented performance estimates do not consider any ion runs in Run5 and Run6 as foreseen in the HL-LHC baseline. Adding these as well in Run5 and Run6 would result in lower proton integrated luminosity by ~ 11%.