Editing Top quark (section)

{{Short description|Type of quark}}
{{use dmy dates|date=February 2023}}
{{Infobox Particle
 |bgcolour    =
 |name        = Top quark
 |image       = Top antitop quark event.svg
 |image_size  = 250px
 |caption     = A collision event involving top quarks
 |num_types   = 
 |composition = [[elementary particle]]
 |statistics  = [[fermionic]]
 |group       = [[quark]]
 |generation  = third 
 |interaction = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]], [[gravity]]
 |particle    = 
 |antiparticle= top antiquark ({{SubatomicParticle|Top antiquark}})
 |theorized   = [[Makoto Kobayashi (physicist)|Makoto Kobayashi]] and [[Toshihide Maskawa]] (1973)
 |discovered  = [[Collider Detector at Fermilab|CDF]] and [[D0 experiment|DØ]] collaborations (1995)
 |symbol      = {{SubatomicParticle|Top quark}}
 |mass        = {{val|172.76|0.3|ul=GeV/c2}}<ref name=PDG2020/>
 |mean_lifetime   = {{val|5|e=-25|u=s}}
 |decay_particle  = {{nowrap|[[bottom quark]] (99.8%)}}<br/>{{nowrap|[[strange quark]] (0.17%)}}<br/>{{nowrap|[[down quark]] (0.007%)}}
 |electric_charge = +{{sfrac| 2 |3}} [[Elementary charge|''e'']]
 |color_charge    = yes
 |spin            = {{sfrac| 1 |2}}&nbsp;[[reduced Planck constant|''ħ'']]
 |topness         = 1
 |weak_isospin    = {{nowrap|[[Chirality (physics)|LH]]: +{{sfrac| 1 |2}}, [[Chirality (physics)|RH]]: 0}}
 |weak_hypercharge= {{nowrap|[[Chirality (physics)|LH]]: +{{sfrac| 1 |3}}, [[Chirality (physics)|RH]]: +{{sfrac| 4 |3}}}}
}} 
The '''top quark''', sometimes also referred to as the '''truth quark''', (symbol: t) is the most massive of all observed [[elementary particle]]s. It derives its mass from its coupling to the [[Higgs field]]. This coupling {{math|''y''}}{{sub|t}} is very close to unity; in the [[Standard Model]] of [[particle physics]], it is the largest (strongest) coupling at the scale of the weak interactions and above. The top quark was discovered in 1995 by the [[Collider Detector at Fermilab|CDF]]<ref name=CDF-1995/> and [[DØ experiment|DØ]]<ref name=D0-1995/> experiments at [[Fermilab]].

Like all other [[quark]]s, the top quark is a [[fermion]] with [[spin-1/2]] and participates in all four [[fundamental interaction]]s: [[gravitation]], [[electromagnetism]], [[weak interaction]]s, and [[strong interaction]]s. It has an [[electric charge]] of +{{sfrac| 2 |3}}&nbsp;[[elementary charge|''e'']]. It has a [[Quark#Mass|mass]] of {{val|172.76|0.3|ul=GeV/c2}},<ref name=PDG2020/> which is close to the [[rhenium]] atom mass.<ref name=Hypertextbook/>{{Verify source|date=December 2024}}<!-- 173.0 GeV/c^2 * 0.931494 u/GeV/c^2 = 185.723 u. --> The [[antiparticle]] of the top quark is the '''top antiquark''' (symbol: {{overline|t}}, sometimes called ''antitop quark'' or simply ''antitop''), which differs from it only in that some of its properties have [[charge conjugation|equal magnitude but opposite sign]].

The top quark interacts with [[gluons]] of the [[strong interaction]] and is typically produced in hadron colliders via this interaction. However, once produced, the top (or antitop) can decay only through the [[weak force]]. It decays to a [[W boson]] and either a [[bottom quark]] (most frequently), a [[strange quark]], or, on the rarest of occasions, a [[down quark]].{{efn|name=predominantly_decays_to_bottom}}

The Standard Model determines the top quark's [[mean lifetime]] to be roughly {{val|5|e=-25|u=s}}.<ref name=Quadt/> This is about a twentieth of the timescale for strong interactions,{{efn|name=exceptionally_fast_weak_interaction}} and therefore it does not [[Hadronization|form hadrons]], giving physicists a unique opportunity to study a "bare" quark (all other quarks [[Hadronization|hadronize]], meaning that they combine with other quarks to form [[hadron]]s and can only be observed as such).

Because the top quark is so massive, its properties allowed indirect determination of the mass of the [[Higgs boson]] (see ''{{slink||Mass and coupling to the Higgs boson}}'' below). As such, the top quark's properties are extensively studied as a means to discriminate between competing theories of new physics beyond the Standard Model. The top quark is the only quark that has been directly observed due to its decay time being shorter than the hadronization time.{{efn|name=exceptionally_fast_weak_interaction}}<ref>{{cite book |last1=Aubert |first1=Jean-Jacques |last2=Gastmans |first2=Raymond |last3=Gérard |first3=Jean-Marc |date=6 December 2012 |title=Particle Physics: Ideas and recent developments |publisher=Springer, Dordrecht |isbn=978-0-7923-6436-8 |pages=69 |url=https://books.google.com/books?id=46bnCAAAQBAJ&q=top+quark+has+been+observed+directly&pg=PA69 |access-date=11 June 2020}}</ref>