Problems and stoppers for γγ , γ μ , μ p colliders using very high energy muons . ∗

It is well known that at linear ee (ee) colliders using laser backscattering one can obtain colliding γγ, γe beams with energy and luminosity comparable to those in ee collisions. In this paper, it is explained why this can not be done at high energy muon colliders. Due to several physics reasons the γγ luminosity is suppressed here by a factor of 10 ! Another option – γ’s from a linear collider and muons from a muon collider – is also discussed (and has no sense either). Of course, one can study γ∗μ and γ∗γ∗ interactions at muon colliders in collisions with virtual photons as it is done now at ee storage rings. Muon-proton colliders are attractive only if the proton beam is cooled and has the same parameters as the muon beam, in which case Lμp ∼ Lμμ.