Particle colliders are microscopes that investigate Nature with the best possible distance resolution. Achieving high resolution requires high energy particle collisions and an energy of 10 TeV would be needed in order to access the next microscopic frontier of a tenth of a billionth of the size of an atom.
Conventional colliders employing protons can reach 10 TeV, but the protons are composite particles and the relevant energy is the one of the collisions between the protons’ constituents. 100 TeV proton energy would be needed to access the 10 TeV scale (see Fig.1). Electrons are instead fundamental particles, but their small mass prevents electron colliders to reach 10 TeV because of the energy loss due to Synchrotron radiation. The muon particles are fundamental and have large enough mass. This motivates the development of the innovative concept of a muon collider (see Fig.2).
Ref.[1] summarises the very recent advances on muon colliders and the R&D plans. It is argued that the muon collider is the most adequate response to contemporary challenges of particle physics by combining different exploration strategies (see Fig.3). Namely, it could discover new particles with presently inaccessible mass as well as precisely studying the Higgs boson. It will uniquely pursue the quantum imprint of new phenomena in novel observables by combining precision with energy. It gives unique access to new physics coupled to muons and delivers beams of neutrinos with unprecendeted properties from the muons decay.
The Particle Physics Projects Prioritization Panel (P5) in the USA reviewed the muon collider project and concluded that [3]:
Although we do not know if a muon collider is ultimately feasible, the road toward it leads to a series of proton beam improvements and neutrino beam facilities, each producing world-class science while performing critical R&D towards a muon collider. At the end of the path is an unparalleled global facility on US soil. This is our Muon Shot
