  An electron-muon collider with an asymmetric collision profile targeting
multi-ab$^{-1}$ integrated luminosity is proposed. This novel collider,
operating at collisions energies of e.g. 20-200 GeV, 50-1000 GeV and 100-3000
GeV, would be able to probe charged lepton flavor violation and measure Higgs
boson properties precisely. The collision of an electron and muon beam leads to
less physics background compared with either an electron-electron or a
muon-muon collider, since electron-muon interactions proceed mostly through
higher order vector boson fusion and vector boson scattering processes. The
asymmetric collision profile results in collision products that are boosted
towards the electron beam side, which can be exploited to reduce beam-induced
background from the muon beam to a large extent. With this in mind, one can
imagine a lepton collider complex, starting from colliding order 10 GeV
electron and muon beams for the first time in history and to probe charged
lepton flavor violation, then to be upgraded to a collider with 50-100 GeV
electron and 1-3 TeV muon beams to measure Higgs properties and search for new
physics, and finally to be transformed to a TeV scale muon muon collider. The
cost should vary from order 100 millions to a few billion dollars,
corresponding to different stages, which make the funding situation more
practical.
