The Minimal Supersymmetric Standard Model (MSSM) is an extension of the Standard Model of particle physics that incorporates the principles of supersymmetry (SUSY). Supersymmetry is a theoretical symmetry between fermions (particles with half-integer spin, like electrons and neutrinos) and bosons (particles with integer spin, like photons and W/Z bosons). The MSSM proposes a partner particle for each particle in the Standard Model, effectively doubling the number of particles.
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The Minimal supersymmetric Standard Model extends the Standard Model by placing its matter fermions in chiral superfields and its gauge bosons in supersymmetric vector multiplets, with two Higgs chiral doublets. The resulting partners include squarks, gauginos and higgsinos.
The paired Higgs fields allow holomorphic up-type and down-type Yukawa couplings and cancel the new higgsino gauge anomalies. A phenomenological model also specifies the MSSM superpotential, soft supersymmetry breaking parameters and whether R-parity is conserved. These choices determine mass eigenstates, mixing and decay chains. For example, neutralinos mix neutral electroweak gauginos and higgsinos. The field content provides a calculable framework, but does not by itself predict one partner mass spectrum or one collider signature.