Bottom quark explained

Composition:	elementary particle
Statistics:	fermionic
Group:	quark
Generation:	third
Interaction:	strong, weak, electromagnetic, gravity
Antiparticle:	bottom antiquark
Theorized:	Makoto Kobayashi and Toshihide Maskawa (1973)
Discovered:	Leon M. Lederman et al. (1977)^[1]
Mass:	( scheme)^[2] (1S scheme)^[3]
Decay Particle:	charm quark or up quark
Electric Charge:	− e
Color Charge:	yes
Spin:	ħ

The bottom quark, beauty quark, or b quark, is an elementary particle of the third generation. It is a heavy quark with a charge of − 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 and Toshihide Maskawa to explain CP violation.^[4] The name "bottom" was introduced in 1975 by Haim Harari.^{[5] [6]}

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.^{[1] [7] [8]} The discovery was confirmed about a year later by the PLUTO and DASP2 Collaborations at the electron-positron collider DORIS at DESY.^{[9] [10]} 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.^{[11] [12]}

While the name "beauty" is sometimes used, "bottom" became the predominant usage by analogy of "top" and "bottom" to "up" and "down".

Distinct character

The bottom quark's "bare" mass is around ^[2]  - 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 and 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).^[13]

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.

Hadrons containing bottom quarks

Some of the hadrons containing bottom quarks include:

• B mesons contain a bottom quark (or its antiparticle) and an up or down quark.
• and mesons contain a bottom quark along with a charm quark or strange quark respectively.
• There are many bottomonium states, for example the 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.).

See also

• Quark model
• B-factory
• B meson

Further reading

• L. Lederman . 1978 . The Upsilon Particle . . 239 . 4 . 72–81 . 10.1038/scientificamerican1078-72 . 1978SciAm.239d..72L .
• Web site: R. Nave . Quarks . . Georgia State University, Department of Physics and Astronomy . 2008-06-29.
• Book: A. Pickering . Constructing Quarks . 114–125 . . 1984 . 978-0-226-66799-7.
• J. Yoh . 1997 . The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story . 424 . 29–42 . Proceedings of Twenty Beautiful Years of Bottom Physics. 1998AIPC..424...29Y . 10.1063/1.55114 . AIP Conference Proceedings .
• Book: Stone, Sheldon . Sheldon Stone . B Decays . 1994 . . . 10.1142/1441 . 978-981-02-0708-3 . 2nd . 636743000.

External links

• History of the discovery of the bottom quark / Upsilon meson

Notes and References

1. 7 August 1977 . Discoveries at Fermilab – Discovery of the Bottom Quark . . 2009-07-24.
2. M. Tanabashi et al. (Particle Data Group) . Review of Particle Physics . 2018 . 10.1103/PhysRevD.98.030001 . 98 . 3 . 030001 . Physical Review D . free . 2018PhRvD..98c0001T . 10044/1/68623 . free .
3. Web site: J. Beringer (Particle Data Group) . PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b', t', Free)' . . 2012 . 2012-12-18 . etal . https://web.archive.org/web/20130512010447/http://pdg.lbl.gov/2012/tables/rpp2012-sum-quarks.pdf . 12 May 2013 . dead .
4. M. . Kobayashi . T. . Maskawa . CP-Violation in the Renormalizable Theory of Weak Interaction . . 49 . 2 . 652–657 . 1973 . 10.1143/PTP.49.652 . 1973PThPh..49..652K . 2433/66179 . free. free .
5. H. . Harari . 1975 . A new quark model for hadrons . . 57 . 3 . 265–269 . 10.1016/0370-2693(75)90072-6 . 1975PhLB...57..265H.
6. Book: Staley , K. W. . 2004 . The Evidence for the Top Quark . 31–33 . 978-0-521-82710-2 . .
7. L. M. . Lederman . 2005 . Logbook: Bottom Quark . . 2 . 8 . dead . https://web.archive.org/web/20061004101845/http://www.symmetrymagazine.org/cms/?pid=1000195 . 4 October 2006.
8. S. W. . Herb . 1977 . Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions . . 39 . 252 . 10.1103/PhysRevLett.39.252 . 1977PhRvL..39..252H . 5 . Hom . D. . Lederman . L. . Sens . J. . Snyder . H. . John Yoh . Yoh . J. . Appel . J. . Brown . B. . Brown . C. . Innes . W. . Ueno . K. . Yamanouchi . T. . Ito . A. . Jöstlein . H. . Kaplan . D. . Kephart . R. . 1155396 . etal.
9. Proceedings of the 19th International Conference on High Energy Physics (Tokyo) . 1978 . G. Flügge . 793–810 . Particle Spectroscopy.
10. Particle Physics: New Evidence from Germany for Fifth Quark . Science . 1978 . 10.1126/science.200.4345.1033 . 200 . 1033–1034 . Arthur L. Robinson . 4345. 1978Sci...200.1033R .
11. http://nobelprize.org/nobel_prizes/physics/laureates/2008/kobayashi-lecture.html 2008 Physics Nobel Prize lecture by Makoto Kobayashi
12. http://nobelprize.org/nobel_prizes/physics/laureates/2008/maskawa-lecture.html 2008 Physics Nobel Prize lecture by Toshihide Maskawa
13. Web site: Transformation of Quark Flavors by the Weak Interaction . Nave . C.R. . HyperPhysics . Department of Physics and Astronomy . Georgia State University . Atlanta, GA .