# Stop squark

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{{Short description|Superpartner of the top quark}}
{{Use dmy dates|date=February 2019}}

In [particle physics](/source/particle_physics), a '''stop squark''', symbol {{SubatomicParticle|top squark}}, is the [superpartner](/source/superpartner) of the [top quark](/source/top_quark) as predicted by [supersymmetry](/source/supersymmetry) (SUSY).  It is a [sfermion](/source/sfermion), which means it is a spin-0 [boson](/source/boson) ([scalar boson](/source/scalar_boson)).  While the top quark is the heaviest known quark, the stop [squark](/source/squark) is actually often the lightest squark in many supersymmetry models.<ref>[http://www-cdf.fnal.gov/physics/new/top/2008/tprop/Stop/Dilepton_Stop_Quark_Search_2Point7invfb.html Search For Pair Production of Stop Quarks Mimicking Top Event Signatures<!-- Bot generated title -->]</ref>

== Overview ==
The stop squark is a key ingredient of a wide range of SUSY models that address the [hierarchy problem](/source/hierarchy_problem) of the [Standard Model](/source/Standard_Model) (SM) in a natural way. A boson partner to the top quark would stabilize the [Higgs boson](/source/Higgs_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 the [Large Hadron Collider](/source/Large_Hadron_Collider). In the generic [R-parity](/source/R-parity) conserving [Minimal Supersymmetric Standard Model](/source/Minimal_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 a [bottom quark](/source/bottom_quark) and a [chargino](/source/chargino), with a subsequent decay of the chargino into the lightest [neutralino](/source/neutralino) (which is often the [lightest supersymmetric particle](/source/lightest_supersymmetric_particle)).

== Evidence ==
Many searches for evidence of the stop squark have been performed by both the [ATLAS](/source/ATLAS_experiment) and [CMS](/source/Compact_Muon_Solenoid) experiments at the LHC but so far no signal has been discovered.<ref>{{cite web|url=https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults|title=ATLAS Supersymmetry Public Results| publisher=ATLAS, CERN |access-date=21 March 2014}}</ref><ref>{{cite web|url=https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS|title=CMS Supersymmetry Public Results| publisher=CMS, CERN |access-date=21 March 2014}}</ref> In January 2019, the CMS Collaboration published findings excluding stop squarks with masses as large as 1230 GeV at 95% (2σ) confidence level.<ref>{{cite journal|url=https://cds.cern.ch/record/2654362|title=Search for supersymmetry in events with a photon, jets, b-jets, and missing transverse momentum in proton-proton collisions at 13 TeV|date=20 January 2019|doi=10.1140/epjc/s10052-019-6926-x |doi-access=free|pmid=31265003 |access-date=30 January 2019 |last1=Sirunyan |first1=A. M. |last2=Tumasyan |first2=A. |last3=Adam |first3=W. |last4=Ambrogi |first4=F. |last5=Asilar |first5=E. |last6=Bergauer |first6=T. |last7=Brandstetter |first7=J. |last8=Dragicevic |first8=M. |last9=Erö |first9=J. |last10=Del Valle |first10=A. E. |last11=Flechl |first11=M. |last12=Frühwirth |first12=R. |last13=Ghete |first13=V. M. |last14=Hrubec |first14=J. |last15=Jeitler |first15=M. |last16=Krammer |first16=N. |last17=Krätschmer |first17=I. |last18=Liko |first18=D. |last19=Madlener |first19=T. |last20=Mikulec |first20=I. |last21=Rad |first21=N. |last22=Rohringer |first22=H. |last23=Schieck |first23=J. |last24=Schöfbeck |first24=R. |last25=Spanring |first25=M. |last26=Spitzbart |first26=D. |last27=Waltenberger |first27=W. |last28=Wittmann |first28=J. |last29=Wulz |first29=C. E. |last30=Zarucki |first30=M. |journal=European Physical Journal C |volume=79 |issue=5 |page=444 |pmc=6537472 |display-authors=1 }}</ref>
==See also==
* [List of hypothetical particles](/source/List_of_hypothetical_particles)

== References ==
{{reflist}}

{{particles}}

Category:Quarks
Category:Supersymmetric quantum field theory
Category:Theoretical physics
Category:Bosons
Category:Subatomic particles with spin 0

{{Particle-stub}}

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Adapted from the Wikipedia article [Stop squark](https://en.wikipedia.org/wiki/Stop_squark) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Stop_squark?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.