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Sfermion

Bosonic superpartner of a fermion

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Source updated July 12, 2025

In supersymmetric extension to the Standard Model (SM) of physics, a sfermion is a hypothetical spin-0 superpartner particle (sparticle) of its associated fermion. Each particle has a superpartner with spin that differs by ⁠1/2⁠. Fermions in the SM have spin-⁠1/2⁠ and, therefore, sfermions have spin 0.

The name 'sfermion' was formed by the general rule of prefixing an 's' to the name of its superpartner, denoting that it is a scalar particle with spin 0. For instance, the electron's superpartner is the selectron and the top quark's superpartner is the stop squark.

One corollary from supersymmetry is that sparticles have the same gauge numbers as their SM partners. This means that sparticle, particle pairs have the same color charge, weak isospin charge, and hypercharge (and consequently electric charge). Unbroken supersymmetry also implies that sparticle, particle pairs have the same mass. This is evidently not the case, since these sparticles would have already been detected. Thus, sparticles must have different masses from the particle partners and supersymmetry is said to be broken.

01Fundamental sfermions

Squarks

Squarks (also quarkinos) are the superpartners of quarks. These include the sup squark, sdown squark, scharm squark, sstrange squark, stop squark, and sbottom squark.

Squarks
Squark	Symbol	Associated quark	Symbol
First generation
Sup squark	${\tilde {u}}$	Up quark	$u$
Sdown squark	${\tilde {d}}$	Down quark	$d$
Second generation
Scharm squark	${\tilde {c}}$	Charm quark	$c$
Sstrange squark	${\tilde {s}}$	Strange quark	$s$
Third generation
Stop squark	${\tilde {t}}$	Top quark	$t$
Sbottom squark	${\tilde {b}}$	Bottom quark	$b$

Sleptons

Sleptons are the superpartners of leptons. These include the selectron, smuon, stau, and their corresponding sneutrino flavors.

Sleptons
Slepton	Symbol	Associated lepton	Symbol
First generation
Selectron	${\tilde {e}}$	Electron	$e$
Selectron sneutrino	${\tilde {\nu }}_{e}$	Electron neutrino	$\nu _{e}$
Second generation
Smuon	${\tilde {\mu }}$	Muon	$\mu$
Smuon sneutrino	${\tilde {\nu }}_{\mu }$	Muon neutrino	$\nu _{\mu }$
Third generation
Stau	${\tilde {\tau }}$	Tau	$\tau$
Stau sneutrino	${\tilde {\nu }}_{\tau }$	Tau neutrino	$\nu _{\tau }$

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Sources and credits

This article is adapted from the Wikipedia article “Sfermion”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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