chargino

Chargino is a charged fermionic mass eigenstate in supersymmetric theories. In the Minimal Supersymmetric Standard Model (MSSM), charginos are mixtures of the charged winos and the charged higgsinos. The two physical states, χ̃1^± and χ̃2^±, carry electric charge ±1 and have spin 1/2.

Their masses and compositions are obtained from a 2×2 chargino mass matrix that depends on the wino mass parameter M2, the higgsino mass parameter μ, and tanβ. Diagonalization yields mχ̃1^± ≤ mχ̃2^±, with the lightest state often playing a crucial role in phenomenology. Depending on parameters, χ̃1^± can be wino-, higgsino-, or mixed-dominated.

Interactions and decays: Charginos couple to W, Z, Higgs bosons and to matter fields via electroweak interactions. In R-parity conserving models, heavier charginos decay to the lightest neutralino χ̃1^0 (the typical LSP) plus W* or via sleptons to leptons and χ̃1^0. This yields collider signatures with missing energy and leptons or jets.

Production and experiments: Charginos can be produced in pairs at e+e− colliders and at hadron colliders through quark-antiquark annihilation and vector-boson fusion. LEP established lower bounds around 100 GeV on χ̃± masses for many spectra; LHC searches have probed higher masses and compressed regions depending on decay chains and the assumed SUSY spectrum.

Notes: Mass degeneracies with neutralinos can create challenging signals, and long-lived charginos may occur in compressed spectra. Charginos are central to collider tests of supersymmetry and to discussions of dark matter in MSSM scenarios.