Editing Bottom quark

{{Short description|Type of quark}}
{{Use dmy dates|date=December 2020}}
{{Infobox particle
| image            =
| caption          =
| num_types        =
| composition      = [[elementary particle]]
| statistics       = [[fermion]]ic
| group            = [[quark]]
| generation       = third
| interaction      = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]], [[gravity]]
| particle         =
| antiparticle     = bottom antiquark ({{Subatomic particle|bottom antiquark}})
| theorized        = [[Makoto Kobayashi (physicist)|Makoto Kobayashi]] and [[Toshihide Maskawa]] (1973)<ref name="KM" />
| discovered       = [[Leon M. Lederman]] et al. (1977)<ref name="FermiPress1977">
{{cite press release
 |date=7 August 1977
 |title=Discoveries at Fermilab – Discovery of the Bottom Quark
 |url=http://www.fnal.gov/pub/inquiring/physics/discoveries/bottom_quark_pr.html
 |publisher=[[Fermilab]]
 |access-date=2009-07-24
}}</ref>
| symbol           = {{Subatomic particle|bottom quark}}
| mass             = {{val|4.18|+0.04|-0.03|ul=GeV/c2}} ([[Minimal subtraction scheme|{{overline|MS}} scheme]])<ref name="PDG2018">
{{cite journal
 |author=M. Tanabashi et al. (Particle Data Group)
 |title=Review of Particle Physics
 |year= 2018
 |doi=10.1103/PhysRevD.98.030001
 |volume=98
 |issue=3
 |pages=030001
 |journal=Physical Review D
 |url=http://pdglive.lbl.gov/DataBlock.action?node=Q005M
 |doi-access=free
 |bibcode=2018PhRvD..98c0001T
 |hdl=10044/1/68623
 |hdl-access=free
}}</ref>{{br}}{{val|4.65|+0.03|-0.03|ul=GeV/c2}} ([[1S scheme]])<ref name="PDG2012">
{{cite web
 |author=J. Beringer ([[Particle Data Group]])
 |url=http://pdg.lbl.gov/2012/tables/rpp2012-sum-quarks.pdf
 |title=PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b′, t′, Free)'
 |publisher=[[Particle Data Group]]
 |year=2012
 |access-date=2012-12-18
 |display-authors=etal
 |archive-url=https://web.archive.org/web/20130512010447/http://pdg.lbl.gov/2012/tables/rpp2012-sum-quarks.pdf
 |archive-date=12 May 2013
 |url-status=dead
}}</ref>
| decay_time       =
| decay_particle   = [[charm quark]] or<br/>[[up quark]]
| electric_charge  = −{{sfrac| 1 |3}}&nbsp;[[Elementary charge|''e'']]
| color_charge     = yes
| spin             = {{sfrac| 1 |2}}&nbsp;[[reduced Planck constant|''ħ'']]
| num_spin_states  =
| 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|−| 2 |3}}}}
}}

The '''bottom quark''', '''beauty quark''', or '''b quark''', is an [[elementary particle]] of the third [[Generation (particle physics)|generation]]. It is a heavy [[quark]] with a charge of −{{sfrac|3}}&nbsp;[[elementary charge|''e'']].

All quarks are described in a similar way by [[electroweak interaction]] and [[quantum chromodynamics]], but the bottom quark has exceptionally low rates of transition to lower-mass quarks. The bottom quark is also notable because it is a product in almost all [[top quark]] decays, and is a frequent decay product of the [[Higgs boson]].

== Name and history ==
The bottom quark was first described theoretically in 1973 by physicists [[Makoto Kobayashi (physicist)|Makoto Kobayashi]] and [[Toshihide Maskawa]] to explain [[CP violation]].<ref name="KM">
{{cite journal
 |last1=Kobayashi |first1=M.
 |last2=Maskawa |first2=T.
 |title=CP-Violation in the Renormalizable Theory of Weak Interaction
 |journal=[[Progress of Theoretical Physics]]
 |volume=49
 |issue=2
 |pages=652–657
 |year=1973
 |bibcode=1973PThPh..49..652K
 |doi=10.1143/PTP.49.652 |doi-access=free
 |hdl=2433/66179 |hdl-access=free
}}</ref> The name "bottom" was introduced in 1975 by [[Haim Harari]].<ref>
{{cite journal
 |last=Harari |first=H.
 |year=1975
 |title=A new quark model for hadrons
 |journal=[[Physics Letters B]]
 |volume=57 |issue=3 |pages=265–269
 |doi=10.1016/0370-2693(75)90072-6
 |bibcode = 1975PhLB...57..265H
}}</ref><ref>
{{cite book
 |last=Staley |first=K. W.
 |year=2004
 |title=The Evidence for the Top Quark
 |pages=31–33
 |isbn=978-0-521-82710-2
 |publisher=[[Cambridge University Press]]
 |url=https://books.google.com/books?id=K7z2oUBzB_wC
}}</ref>

The evidence for the bottom quark was first obtained in 1977 by the [[Fermilab]] [[E288 experiment]] team led by [[Leon M. Lederman]], when proton-nucleon collisions produced [[bottomonium]] decaying to pairs of [[muon]]s.<ref name="FermiPress1977"/><ref>
{{cite journal
 |first=L. M. |last=Lederman 
 |year=2005 
 |url=http://www.symmetrymagazine.org/cms/?pid=1000195 
 |title=Logbook: Bottom Quark 
 |journal=[[Symmetry Magazine]] 
 |volume=2 
 |issue=8 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20061004101845/http://www.symmetrymagazine.org/cms/?pid=1000195 
 |archive-date=4 October 2006
}}</ref><ref>
{{cite journal
 |last1=Herb |first1=S. W.
 |year=1977
 |title=Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions
 |journal=[[Physical Review Letters]]
 |volume=39 |page=252
 |doi=10.1103/PhysRevLett.39.252
 |bibcode=1977PhRvL..39..252H
 |issue=5
 |last2=Hom |first2=D.
 |last3=Lederman |first3=L.
 |last4=Sens |first4=J.
 |last5=Snyder |first5=H.
 |last6=Yoh |first6=J. |author6-link=John Yoh
 |last7=Appel |first7=J.
 |last8=Brown |first8=B.
 |last9=Brown |first9=C.
 |last10=Innes |first10=W.
 |last11=Ueno |first11=K.
 |last12=Yamanouchi |first12=T.
 |last13=Ito |first13=A.
 |last14=Jöstlein |first14=H.
 |last15=Kaplan |first15=D.
 |last16=Kephart |first16=R.
 |osti=1155396
 |display-authors=etal
 |url=https://www.osti.gov/biblio/1155396
|url-access=subscription
 }}</ref> The discovery was confirmed about a year later by the PLUTO and DASP2 Collaborations at the electron-positron collider [[DORIS (particle accelerator)|DORIS]] at [[DESY]].<ref>{{cite journal | journal = Proceedings of the 19th International Conference on High Energy Physics (Tokyo) | year = 1978 | author = G. Flügge | pages=793–810 | url = https://cds.cern.ch/record/870709/ | title = Particle Spectroscopy}}</ref><ref name=science1978>{{cite journal | title = Particle Physics: New Evidence from Germany for Fifth Quark | journal = Science | year = 1978 | doi=10.1126/science.200.4345.1033 | volume = 200 | pages=1033–1034 | author = Arthur L. Robinson | issue = 4345| bibcode = 1978Sci...200.1033R }}</ref> It was reported at the time that DESY scientists were in favor of the name "beauty", while the American scientists tended towards "bottom".<ref name=science1978 />

Kobayashi and Maskawa won the 2008 [[Nobel Prize in Physics]] for their explanation of CP-violation.<ref>[http://nobelprize.org/nobel_prizes/physics/laureates/2008/kobayashi-lecture.html 2008 Physics Nobel Prize lecture by Makoto Kobayashi]</ref><ref>[http://nobelprize.org/nobel_prizes/physics/laureates/2008/maskawa-lecture.html 2008 Physics Nobel Prize lecture by Toshihide Maskawa]</ref>

While the name "beauty" is sometimes used, "bottom" became the predominant usage by analogy of [[top quark|"top"]] and "bottom" to [[up quark|"up"]] and [[down quark|"down"]].{{Citation needed|date=December 2020}}

== Distinct character ==
The bottom quark's [[Quark#Mass|"bare" mass]] is around {{val|4.18|ul=GeV/c2}}<ref name="PDG2018"/> &ndash; a bit more than four times the mass of a [[proton]], and many orders of magnitude larger than common "light" quarks.

Although it almost exclusively transitions from or to a [[top quark]], the bottom quark can decay into either an [[up quark]] or [[charm quark]] via the [[weak interaction]]. [[CKM matrix]] elements {{mvar|V}}{{sub|ub}} and {{mvar|V}}{{sub|cb}} specify the rates, where both these decays are suppressed, making lifetimes of most bottom particles (~10<sup>−12</sup>&nbsp;s) somewhat longer than those of charmed particles (~10<sup>−13</sup>&nbsp;s), but shorter than those of strange particles (from ~10<sup>−10</sup> to ~10<sup>−8</sup>&nbsp;s).<ref>
{{cite web
 | title=Transformation of Quark Flavors by the Weak Interaction
 | editor-last=Nave | editor-first=C.R.
 | website=HyperPhysics
 | department=Department of Physics and Astronomy
 | publisher=Georgia State University
 | place=Atlanta, GA 
 | url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/qrkdec.html
}}</ref>

The combination of high mass and low transition rate gives experimental [[particle collider|collision]] byproducts containing a bottom quark a distinctive signature that makes them relatively easy to identify using a technique called "[[B-tagging]]". For that reason, [[meson]]s containing the bottom quark are exceptionally long-lived for their mass, and are the easiest particles to use to investigate [[CP violation]]. Such experiments are being performed at the [[BaBar experiment|BaBar]], [[Belle Experiment|Belle]] and [[LHCb]] experiments.

== Hadrons containing bottom quarks ==
{{Main|list of baryons|list of mesons}}
Some of the [[hadron]]s containing bottom quarks include:
* [[B meson]]s contain a bottom quark (or its [[antiparticle]]) and an [[up quark|up]] or [[down quark]].
* {{SubatomicParticle|Charmed B}} and {{SubatomicParticle|Strange B}} mesons contain a bottom quark along with a [[charm quark]] or [[strange quark]] respectively.
* There are many [[bottomonium]] states, for example the [[Upsilon meson|{{SubatomicParticle|Upsilon}} meson]] and [[chi b (3P)|χ<sub>b</sub>(3P)]], the first particle discovered in [[Large Hadron Collider|LHC]].  These consist of a bottom quark and its antiparticle.
* Bottom [[baryon]]s have been observed, and are named in analogy with strange baryons (e.g. {{SubatomicParticle|Bottom Lambda0}}).

== See also ==
* [[Quark model]]
* [[B-factory]]
* [[B meson]]

== References ==
{{reflist|30em}}

== Further reading ==
* {{cite journal |author=L. Lederman |year=1978 |title=The Upsilon Particle |journal=[[Scientific American]] |volume=239 |issue=4 |pages=72–81 |doi=10.1038/scientificamerican1078-72 |bibcode = 1978SciAm.239d..72L }}
* {{cite web |author=R. Nave |title=Quarks |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html |work=[[HyperPhysics]] |publisher=[[Georgia State University]], Department of Physics and Astronomy |access-date=2008-06-29}}
* {{cite book |author=A. Pickering |title=Constructing Quarks |pages=114–125 |publisher=[[University of Chicago Press]] |year=1984 |isbn=978-0-226-66799-7}}
* {{cite conference |author=J. Yoh |year=1997 |title=The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story |volume=424 |pages=29–42 |url=http://lss.fnal.gov/archive/1997/conf/Conf-97-432-E.pdf |conference=Proceedings of Twenty Beautiful Years of Bottom Physics|bibcode=1998AIPC..424...29Y |doi=10.1063/1.55114 |series=AIP Conference Proceedings }}
* {{cite book |last=Stone |first=Sheldon |author-link=Sheldon Stone |title=B Decays |date=1994 |publisher=[[World Scientific]] |location=[[Syracuse University]] |doi=10.1142/1441 |isbn=978-981-02-0708-3 |edition=2nd |url=https://doi.org/10.1142/1441 |oclc=636743000}}

== External links ==
* [http://history.fnal.gov/botqrk.html History of the discovery of the bottom quark / Upsilon meson] {{Webarchive|url=https://web.archive.org/web/20170824104835/http://history.fnal.gov/botqrk.html |date=24 August 2017 }}
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{{DEFAULTSORT:Bottom Quark}}
[[Category:Elementary particles]]
[[Category:Quarks]]