Por Tiziano Camporesi (LIP).
The principal recommendations of the 2019 ESPP for future accelerator Initiatives was that: "An electron-positron Higgs factory is the highest priority for the next collider".
We are now in the process of the next 5 year review and in this respect we support FCC-ee and FCC-hh as the preferred option for CERN's future, as it addresses all the recommendations of the ESPP.
The guidance for the 2025 ESPP requests, in addition to the preferred option, the inclusion of "prioritised alternatives to be pursued if the chosen preferred option turns out not to be feasible or competitive". So far the proposed alternatives to the preferred FCC option include linear, muon colliders and LHeC accelerators.
In response to this request we propose reusing the existing LHC tunnel for an electron-positron collider, called LEP3, as a back-up alternative if the FCC cannot proceed. LEP3 leverages much of the R&D conducted for FCC-ee, offers high-precision studies of Z, W, and Higgs bosons below the t-tbar threshold, and offers potential physics performance comparable or superior to other fallback options at a lower cost while supporting continued R&D towards a next-generation energy frontier machine.
