smuons

In particle physics, a smuon is the supersymmetric partner of the muon. In supersymmetry, each Standard Model fermion has a bosonic superpartner; the smuon is a scalar lepton (a slepton) with electric charge -1 and spin 0. There are two weak eigenstates, the left-handed smuon (smuon_L) and the right-handed smuon (smuon_R), which in general mix to form mass eigenstates smuon_1 and smuon_2.

Smuons interact via electroweak forces and couple to muons, neutralinos, and charginos. Their masses arise from soft SUSY-breaking terms and depend on the supersymmetry-breaking scenario. In many models, smuon_1 is lighter than smuon_2.

At high-energy colliders, smuons can be produced in pairs through Drell-Yan processes and, depending on the spectrum and conservation of R-parity, decay to a muon and the lightest neutralino (the LSP) or to other neutralinos or gravitinos in gauge- or gravity-mediated scenarios. If R-parity is conserved, the experimental signature is a pair of muons plus missing transverse energy from the undetected LSPs.

In the Minimal Supersymmetric Standard Model and its extensions, smuons are part of the slepton sector alongside selectrons and staus. They have not been observed experimentally as of 2025; collider searches have placed lower bounds on their masses, typically in the several hundred GeV range, depending on the neutralino mass and decay channels.

Research status: ongoing collider experiments continue to probe smuon production and decay channels; future runs or higher-energy colliders could extend sensitivity.