Bottom quark

The bottom quark was first described theoretically in 1973 by physicists Makoto Kobayashi and Toshihide Maskawa to explain CP violation.

{{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

}} The name "bottom" was introduced in 1975 by Haim Harari.

{{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

}}

{{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

}}

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 muons.

{{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

}}

{{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

}} The discovery was confirmed about a year later by the PLUTO and DASP2 Collaborations at the electron-positron collider DORIS at DESY.{{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}}{{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 }} It was reported at the time that DESY scientists were in favor of the name "beauty", while the American scientists tended towards "bottom".

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

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

The bottom quark's "bare" mass is around {{val|4.18|ul=GeV/c2}} – 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 (~10⁻¹² s) somewhat longer than those of charmed particles (~10⁻¹³ s), but shorter than those of strange particles (from ~10⁻¹⁰ to ~10⁻⁸ s).

{{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

}}

The combination of high mass and low transition rate gives experimental 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, mesons 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, Belle and LHCb experiments.

{{Main|list of baryons|list of mesons}}

Some of the hadrons containing bottom quarks include:

• B mesons contain a bottom quark (or its antiparticle) and an 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 and χ_b(3P), the first particle discovered in LHC. These consist of a bottom quark and its antiparticle.
• Bottom baryons have been observed, and are named in analogy with strange baryons (e.g. {{SubatomicParticle|Bottom Lambda0}}).

• Quark model
• B-factory
• B meson

{{reflist|30em}}

• {{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}}

• [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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Category:Elementary particles

Category:Quarks