For the episode of the American TV series Angel, see Supersymmetry (Angel)
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In particle physics, supersymmetry (SUSY) is a proposed extension of spacetime symmetry that relates two basic classes of elementary particles: bosons, which have an integer-valued spin, and fermions, which have a half-integer spin. Each particle from one group is associated with a particle from the other, called its superpartner, whose spin differs by a half-integer. In a theory with perfectly unbroken supersymmetry, each pair of superpartners shares the same mass and internal quantum numbers besides spin - for example, a "selectron" (superpartner electron) would be a boson version of the electron, and would have the same mass energy and thus be equally easy to find in the lab. However, since no superpartners have been observed yet, supersymmetry must be a spontaneously broken symmetry if it exists. If supersymmetry is a true symmetry of nature, it would explain many mysterious features of particle physics and would help solve paradoxes such as the cosmological constant problem. The Minimal Supersymmetric Standard Model is one of the best studied candidates for physics beyond the Standard Model.The failure of the Large Hadron Collider to find evidence for supersymmetry has led some physicists to suggest that the theory should be abandoned as a solution to such problems, as any superpartners that exist would now need to be too massive to solve the paradoxes anyway. Experiments with the Large Hadron Collider also yielded extremely rare particle decay events which casts doubt on many versions of supersymmetry.Supersymmetry differs notably from currently known symmetries in that it establishes a symmetry between classical and quantum physics, which up to now has not been observed in any other domain. While any number of bosons can occupy the same quantum state, for fermions this is not possible because of the exclusion principle, which allows only one fermion in a given state. But when the occupation numbers become large, quantum physics approaches the classical limit. This means that while bosons also exist in classical physics, fermions do not. That makes it difficult to expect that bosons possess the same quantum numbers as fermions. There is only indirect evidence for the existence of supersymmetry, primarily in the form of evidence for gauge coupling unification. However this refers only to electroweak and strong interactions and does not provide the ultimate unification of all interactions, since it leaves gravitation untouched.
^ Sean Carroll, Dark Matter, Dark Energy: The Dark Side of the Universe, The Teaching Company, Guidebook Part 2 page 60, Accessed Oct. 7, 2013, "...Supersymmetry -- A hypothetical symmetry relating bosons to fermions..."
^ Wolchover, Natalie (November 29, 2012). "Supersymmetry Fails Test, Forcing Physics to Seek New Ideas". Scientific American.
^ M. Hogenboom (24 July 2013). "Ultra-rare decay confirmed in LHC". BBC. Retrieved 2013-08-18.
^ Richard M. Weiner (2013). "Spin-statistics-quantum number connection and supersymmetry". Physical Review D 87 (5). arXiv:1302.0969. Bibcode:2013PhRvD..87e5003W. doi:10.1103/PhysRevD.87.055003.
^ Gordon L. Kane, The Dawn of Physics Beyond the Standard Model, Scientific American, June 2003, page 60 and The frontiers of physics, special edition, Vol 15, #3, page 8 "Indirect evidence for supersymmetry comes from the extrapolation of interactions to high energies."