Fermion

<h2 id="elementary-fermions">Elementary fermions</h2>

<p>The <a href="/facts/Standard_Model/LhVGf9ow">Standard Model</a> recognizes two types of elementary fermions: <a href="/facts/Quark/hwuuVkV5">quarks</a> and <a href="/facts/Lepton/X4a6MGop">leptons</a>. In all, the model distinguishes 24 different fermions. There are six quarks (<a href="/facts/Up_quark/Aw3Vp3vk">up</a>, <a href="/facts/Down_quark/Nq10ayEE">down</a>, <a href="/facts/Strange_quark/VDWd3ky0">strange</a>, <a href="/facts/Charm_quark/RLduBtpL">charm</a>, <a href="/facts/Bottom_quark/2s4rJRSo">bottom</a> and <a href="/facts/Top_quark/82qd7NPI">top</a>), and six leptons (<a href="/facts/Electron/L0KBo5cW">electron</a>, <a href="/facts/Electron_neutrino/e5hQPWIQ">electron neutrino</a>, <a href="/facts/Muon/BP2fLVIR">muon</a>, <a href="/facts/Muon_neutrino/A8kPHDKd">muon neutrino</a>, <a href="/facts/Tauon/6DW8j6PC">tauon</a> and <a href="/facts/Tauon_neutrino/GGIb4W5b">tauon neutrino</a>), along with the corresponding <a href="/facts/Antiparticle/7Ic43ThI">antiparticle</a> of each of these.
</p><p>Mathematically, there are many varieties of fermions, with the three most common types being:
</p>
<ul><li><a href="/facts/Weyl_fermion/8KhWTFaM">Weyl fermions</a> (massless),</li>
<li><a href="/facts/Dirac_fermion/gJuu9J69">Dirac fermions</a> (massive), and</li>
<li><a href="/facts/Majorana_fermion/39gzL0Nv">Majorana fermions</a> (each its own antiparticle).</li></ul>
<p>Most Standard Model fermions are believed to be Dirac fermions, although it is unknown at this time whether the <a href="/facts/Neutrino/yGWVfSg2">neutrinos</a> are Dirac or Majorana fermions (or both). Dirac fermions can be treated as a combination of two Weyl fermions.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>: 106  In July 2015, Weyl fermions have been experimentally realized in <a href="/facts/Weyl_semimetal/FjWk1AMl">Weyl semimetals</a>.
</p>
<h2 id="composite-fermions">Composite fermions</h2>
<p class="note">See also: <a href="/facts/List_of_particles/FwR0Ab6u">List of particles § Composite particles</a></p>
<p>Composite particles (such as <a href="/facts/Hadron/C0sd1zty">hadrons</a>, nuclei, and atoms) can be bosons or fermions depending on their constituents. More precisely, because of the relation between spin and statistics, a particle containing an odd number of fermions is itself a fermion. It will have half-integer spin.
</p><p>Examples include the following:
</p>
<ul><li>A baryon, such as the proton or neutron, contains three fermionic quarks.</li>
<li>The nucleus of a <a href="/facts/Carbon-13/Iho4LUtW">carbon-13</a> atom contains six protons and seven neutrons.</li>
<li>The atom <a href="/facts/Helium-3/SmPC5oT3">helium-3</a> (3He) consists of two protons, one neutron, and two electrons. The <a href="/facts/Deuterium/Bv4wfCkw">deuterium</a> atom consists of one proton, one neutron, and one electron.</li></ul>
<p>The number of bosons within a composite particle made up of simple particles bound with a potential has no effect on whether it is a boson or a fermion.
</p><p>Fermionic or bosonic behavior of a composite particle (or system) is only seen at large (compared to size of the system) distances. At proximity, where spatial structure begins to be important, a composite particle (or system) behaves according to its constituent makeup.
</p><p>Fermions can exhibit bosonic behavior when they become loosely bound in pairs. This is the origin of superconductivity and the <a href="/facts/Superfluid/QuePDujN">superfluidity</a> of helium-3: in superconducting materials, electrons interact through the exchange of <a href="/facts/Phonon/tflWW6vw">phonons</a>, forming <a href="/facts/Cooper_pair/uHILVyXu">Cooper pairs</a>, while in helium-3, Cooper pairs are formed via spin fluctuations.
</p><p>The quasiparticles of the <a href="/facts/Fractional_quantum_Hall_effect/bkRtdmxX">fractional quantum Hall effect</a> are also known as <a href="/facts/Composite_fermions/V8z6EGcu">composite fermions</a>; they consist of electrons with an even number of quantized vortices attached to them.
</p>
<h2 id="see-also">See also</h2>

<ul><li><a href="/facts/Anyon/hfgpCFjf">Anyon</a>, 2D quasiparticles</li>
<li><a href="/facts/Chirality_(physics)/H8Xbcvzt">Chirality (physics)</a>, left-handed and right-handed</li>
<li><a href="/facts/Fermionic_condensate/WlqsAJtp">Fermionic condensate</a></li>
<li><a href="/facts/Weyl_semimetal/FjWk1AMl">Weyl semimetal</a></li>
<li><a href="/facts/Fermionic_field/KKaGVgX6">Fermionic field</a></li>
<li><a href="/facts/Identical_particles/qg0mHeVR">Identical particles</a></li>
<li><a href="/facts/Kogut%25E2%2580%2593Susskind_fermion/bUUQsA16">Kogut–Susskind fermion</a>, a type of lattice fermion</li>
<li><a href="/facts/Majorana_fermion/39gzL0Nv">Majorana fermion</a>, each its own antiparticle</li>
<li><a href="/facts/Parastatistics/LuTVIFs4">Parastatistics</a></li>
<li><a href="/facts/Skyrmion/Dw0l6Q0m">Skyrmion</a>, a hypothetical particle</li></ul>

<h2 id="notes">Notes</h2>

<h2 id="external-links">External links</h2>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Weiner, Richard M. (4 March 2013). "Spin-statistics-quantum number connection and supersymmetry". Physical Review D. 87 (5): 055003–05. arXiv:1302.0969. Bibcode:2013PhRvD..87e5003W. doi:10.1103/physrevd.87.055003. ISSN 1550-7998. S2CID 118571314. Retrieved 28 March 2022. <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.055003" target="_blank">https://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.055003</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Notes on Dirac's lecture Developments in Atomic Theory at Le Palais de la Découverte, 6 December 1945, UKNATARCHI Dirac Papers BW83/2/257889. See note 64 on page 331 in "The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom" by Graham Farmelo <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Morii, T.; Lim, C. S.; Mukherjee, S. N. (1 January 2004). The Physics of the Standard Model and Beyond. World Scientific. ISBN 978-981-279-560-1. <a href="978-981-279-560-1" target="_blank">978-981-279-560-1</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Fermion open-in-new

Fermion