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R-hadrons are hypothetical particles composed of a Supersymmetric particle and at least one quark. == Theory == Only a few of the current supersymmetry theories predict the existence of R-hadrons, since in most of the parameter space all the supersymmetric particles are so separated in mass that their decays are very fast (with the exception of the LSP, which is stable in all the SUSY theories with R-parity). R-hadrons are possible when a colored (in the sense of QCD) supersymmetric particle (e.g., a gluino or a squark) has a mean lifetime longer than the typical hadronization time scale, and so QCD bound states are formed with ordinary partons (quarks and gluons), in analogy with the ordinary hadrons. One example of a theory predicting observable R-hadrons is Split SUSY. Its main feature is, in fact, that all the new bosons are at a very high mass scale, and only the new fermions are at the TeV scale, i.e. accessible by the ATLAS and CMS experiments in collisions at LHC. One of such new fermions would be the gluino (spin 1/2, as dictated for the supersymmetric partner of a spin 1 boson, the gluon). The gluino, being colored, can only decay to other colored particles. But R-parity prevents a direct decay to quarks and/or gluons, and on the other hand the only other colored supersymmetric particles are the squarks, that being bosons (spin 0, being the partners of the spin 1/2 quarks) have a much higher mass in Split SUSY. All this, together, implies that the decay of the gluino can only go through a virtual particle, a high-mass squark. The mean decay time depends on the mass of the intermediate virtual particle, and in this case can be very long. This gives a unique opportunity to observe a SUSY particle directly, in a particle detector, instead of deducing it by reconstructing its decay chain or by the momentum imbalance (as in the case of the LSP). In other theories belonging to the SUSY family, the same role can be played by the lightest squark (usually the ''stop'', i.e. the partner of the top quark). In the following, for sake of illustration, the R-hadron will be assumed to originate from a gluino created in a collision at LHC, but the observational features are completely general. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「R-hadron」の詳細全文を読む スポンサード リンク
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