Inparticle physics, astop squark, symbolt͂, is thesuperpartner of thetop quark as predicted bysupersymmetry (SUSY). It is asfermion, which means it is a spin-0boson (scalar boson). While the top quark is the heaviest known quark, the stopsquark is actually often the lightest squark in many supersymmetry models.[1]
The stop squark is a key ingredient of a wide range of SUSY models that address thehierarchy problem of theStandard Model (SM) in a natural way. A boson partner to the top quark would stabilize theHiggs boson mass against quadratically divergent quantum corrections, provided its mass is close to the electroweak symmetry breaking energy scale. If this was the case then the stop squark would be accessible at theLarge Hadron Collider. In the genericR-parity conservingMinimal Supersymmetric Standard Model (MSSM) the scalar partners of right-handed and left-handed top quarks mix to form two stop mass eigenstates. Depending on the specific details of the SUSY model and the mass hierarchy of the sparticles, the stop might decay into abottom quark and achargino, with a subsequent decay of the chargino into the lightestneutralino (which is often thelightest supersymmetric particle).
Many searches for evidence of the stop squark have been performed by both theATLAS andCMS experiments at the LHC but so far no signal has been discovered.[2][3] In January 2019, the CMS Collaboration published findings excluding stop squarks with masses as large as 1230 GeV at 95% (2σ) confidence level.[4]
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