Bottom quark

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Bottom quark
Composition Elementary particle
Statistics Fermionic
Generation Third
Interactions Strong, Weak, Electromagnetic force, Gravity
Antiparticle Bottom antiquark (
Theorized Makoto Kobayashi and Toshihide Maskawa (1973)[1]
Discovered Leon M. Lederman et al. (1977)[2]

(MS scheme)[3]

(1S scheme)[3]
Decays into

Charm quark, or

up quark
Electric charge 1/3 e
Color charge Yes
Spin 1/2
Weak isospin LH: −1/2, RH: 0
Weak hypercharge LH: 1/3, RH: −2/3

The bottom quark or b quark, also known as the beauty quark, is a third-generation quark with a charge of −1/3 e. Although all quarks are described in a similar way by quantum chromodynamics, the bottom quark's large bare mass (around 4.2 GeV/c2,[3] a bit more than four times the mass of a proton), combined with low values of the CKM matrix elements Vub and Vcb, gives it a distinctive signature that makes it relatively easy to identify experimentally (using a technique called B-tagging). Because three generations of quark are required for CP violation (see CKM matrix), mesons containing the bottom quark are the easiest particles to use to investigate the phenomenon; such experiments are being performed at the BaBar, Belle and LHCb experiments.

The bottom quark is also notable because it is a product in almost all top quark decays, and is a frequent decay product for the Higgs boson. The bottom quark was theorized in 1973 by physicists Makoto Kobayashi and Toshihide Maskawa to explain CP violation.[1] The name "bottom" was introduced in 1975 by Haim Harari.[4][5] The bottom quark was discovered in 1977 by the Fermilab E288 experiment team led by Leon M. Lederman, when collisions produced bottomonium.[2][6][7] Kobayashi and Maskawa won the 2008 Nobel Prize in Physics for their explanation of CP-violation.[8][9] On its discovery, there were efforts to name the bottom quark "beauty", but "bottom" became the predominant usage.

The bottom quark can decay into either an up quark or charm quark via the weak interaction. Both these decays are suppressed by the CKM matrix, making lifetimes of most bottom particles (~10−12 s) somewhat higher than those of charmed particles (~10−13 s), but lower than those of strange particles (from ~10−10 to ~10−8 s).

Hadrons containing bottom quarks[edit]

Some of the hadrons containing bottom quarks include:

See also[edit]


  1. ^ a b M. Kobayashi; T. Maskawa (1973). "CP-Violation in the Renormalizable Theory of Weak Interaction". Progress of Theoretical Physics. 49 (2): 652–657. Bibcode:1973PThPh..49..652K. doi:10.1143/PTP.49.652. 
  2. ^ a b "Discoveries at Fermilab – Discovery of the Bottom Quark" (Press release). Fermilab. 7 August 1977. Retrieved 2009-07-24. 
  3. ^ a b c J. Beringer (Particle Data Group); et al. (2012). "PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b′, t′, Free)'" (PDF). Particle Data Group. Retrieved 2012-12-18. 
  4. ^ H. Harari (1975). "A new quark model for hadrons". Physics Letters B. 57 (3): 265. Bibcode:1975PhLB...57..265H. doi:10.1016/0370-2693(75)90072-6. 
  5. ^ K.W. Staley (2004). The Evidence for the Top Quark. Cambridge University Press. pp. 31–33. ISBN 978-0-521-82710-2. 
  6. ^ L.M. Lederman (2005). "Logbook: Bottom Quark". Symmetry Magazine. 2 (8). Archived from the original on 4 October 2006. 
  7. ^ S.W. Herb; Hom, D.; Lederman, L.; Sens, J.; Snyder, H.; Yoh, J.; Appel, J.; Brown, B.; Brown, C.; Innes, W.; Ueno, K.; Yamanouchi, T.; Ito, A.; Jöstlein, H.; Kaplan, D.; Kephart, R.; et al. (1977). "Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions". Physical Review Letters. 39 (5): 252. Bibcode:1977PhRvL..39..252H. doi:10.1103/PhysRevLett.39.252. 
  8. ^ 2008 Physics Nobel Prize lecture by Makoto Kobayashi
  9. ^ 2008 Physics Nobel Prize lecture by Toshihide Maskawa

Further reading[edit]

External links[edit]