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Up quark
open-in-new
<p>The up quark or u quark (symbol: u) is the lightest of all <a href="/facts/Quark/hwuuVkV5">quarks</a>, a type of <a href="/facts/Elementary_particle/CTFDM97U">elementary particle</a>, and a significant constituent of <a href="/facts/Matter/osyc04UN">matter</a>. It, along with the <a href="/facts/Down_quark/Nq10ayEE">down quark</a>, forms the <a href="/facts/Neutron/oRCM1geb">neutrons</a> (one up quark, two down quarks) and <a href="/facts/Proton/clCjepXP">protons</a> (two up quarks, one down quark) of <a href="/facts/Atomic_nucleus/orpIm5Xl">atomic nuclei</a>. It is part of the <a href="/facts/Generation_(physics)/hAbgvUfV">first generation</a> of matter, has an <a href="/facts/Electric_charge/xxsBfmlB">electric charge</a> of +2/3 <a href="/facts/Elementary_charge/lPcj6CoQ"><i>e</i></a> and a <a href="/facts/Quark/hwuuVkV5">bare mass</a> of 2.2+0.5−0.4 <a href="/facts/Electronvolt/YMT1fqX9">MeV/<i>c</i>2</a>. Like all <a href="/facts/Quark/hwuuVkV5">quarks</a>, the up quark is an <a href="/facts/Elementary_particle/CTFDM97U">elementary</a> <a href="/facts/Fermion/LEckdDsR">fermion</a> with <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a> <a href="/facts/Spin-1%2f2/3I929M4X">1/2</a>, and experiences all four <a href="/facts/Fundamental_interaction/WrFEJaFl">fundamental interactions</a>: <a href="/facts/Gravitation/bqAN7DdQ">gravitation</a>, <a href="/facts/Electromagnetism/oAkmALHT">electromagnetism</a>, <a href="/facts/Weak_interaction/f6upmKMs">weak interactions</a>, and <a href="/facts/Strong_interaction/JjRsKcLg">strong interactions</a>. The <a href="/facts/Antiparticle/7Ic43ThI">antiparticle</a> of the up quark is the up antiquark (sometimes called <i>antiup quark</i> or simply <i>antiup</i>), which differs from it only in that some of its properties, such as <a href="/facts/Electric_charge/xxsBfmlB">charge</a> have <a href="/facts/Additive_inverse/n8gKUmCf">equal magnitude but opposite sign</a>. </p><p>Its existence (along with that of the <a href="/facts/Down_quark/Nq10ayEE">down</a> and <a href="/facts/Strange_quark/VDWd3ky0">strange quarks</a>) was postulated in 1964 by <a href="/facts/Murray_Gell-Mann/7yg75mjR">Murray Gell-Mann</a> and <a href="/facts/George_Zweig/90Ah73xH">George Zweig</a> to explain the <a href="/facts/Eightfold_Way_(physics)/xDtTrHK2">Eightfold Way</a> classification scheme of <a href="/facts/Hadron/C0sd1zty">hadrons</a>. The up quark was first observed by experiments at the <a href="/facts/Stanford_Linear_Accelerator_Center/CzX2afas">Stanford Linear Accelerator Center</a> in 1968. </p>