supersymmetry, in physics, theory concerning the relationship of the elementary particles called boson to those known as fermions, and vice versa, and linking the four fundamental forces. In supersymmetry every ordinary elementary particle has as its counterpart a supersymmetric particle, or superparticle, with similar properties except for angular momentum, or spin, which differs by a half unit. According to supersymmetry, each ordinary fermion has a superpartner that is a boson, and each ordinary boson has a superpartner that is a fermion. The superpartners of fermions are named by adding the prefix s- to the fermion's name, e.g., the squark is the quark's counterpart, and those of bosons by adding the suffix -ino to the root of the boson's name, e.g., the photino is the photon's counterpart. Proof of the theory—discovery of the predicted particles through their creation and detection in a particle accelerator—requires extremely high energy levels, and it was hoped that the Large Hadron Collider would provide evidence for supersymmetry, but a lack of evidence for the existence of superpartner particles as predicted by the simple version of supersymmetry has called the theory into question. See also string theory.

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