The physics case for an electron-muon collider

TL;DR

This paper advocates for an electron-muon collider with asymmetric collision profiles, capable of probing lepton flavor violation and Higgs properties at various energy scales, offering a promising and cost-effective path for future particle physics research.

Contribution

It introduces a novel asymmetric electron-muon collider concept with staged energy upgrades, reducing background and enabling diverse physics measurements.

Findings

Proposed collider can operate at multiple energy scales from 20 GeV to 3 TeV.

Asymmetric collisions reduce background and improve measurement precision.

Staged development approach makes the project financially feasible.

Abstract

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.