Bottom quark

Bottom quark

Bottom quark
Composition Elementary particle
Statistics Fermionic
Generation Third
Interactions Strong, Weak, Electromagnetic force, Gravity
Symbol b
Antiparticle Bottom antiquark (b)
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 13 e
Color charge Yes
Spin 12
Weak isospin LH: −12, RH: 0
Weak hypercharge LH: 13, RH: −23

The bottom quark or b quark, also known as the beauty quark, is a third-generation quark with a charge of −13 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 1
  • See also 2
  • References 3
  • Further reading 4
  • External links 5

Hadrons containing bottom quarks

Some of the hadrons containing bottom quarks include:

See also


  1. ^ a b M. Kobayashi; T. Maskawa (1973). "CP-Violation in the Renormalizable Theory of Weak Interaction".  
  2. ^ a b "Discoveries at Fermilab – Discovery of the Bottom Quark" (Press release).  
  3. ^ a b c J. Beringer ( 
  4. ^ H. Harari (1975). "A new quark model for hadrons".  
  5. ^ K.W. Staley (2004). The Evidence for the Top Quark.  
  6. ^ L.M. Lederman (2005). "Logbook: Bottom Quark".  
  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".  
  8. ^ 2008 Physics Nobel Prize lecture by Makoto Kobayashi
  9. ^ 2008 Physics Nobel Prize lecture by Toshihide Maskawa

Further reading

  • L. Lederman (1978). "The Upsilon Particle".  
  • R. Nave. "Quarks".  
  • A. Pickering (1984). Constructing Quarks.  
  • J. Yoh (1997). "The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story" (PDF). Proceedings of Twenty Beautiful Years of Bottom Physics.  

External links

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