Lambda baryon

Lambda baryon

The Lambda baryons are a family of subatomic hadron particles which have the symbols Λ0
, Λ+
, Λ0
and Λ+
and have +1 elementary charge or are neutral. They are baryons containing three different quarks: one up, one down, and one third quark, which can be either a strange (Λ0
), a charm (Λ+
), a bottom (Λ0
) or a top (Λ+
) quark. The top Lambda is not expected to be observed as the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s.[1] This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.

The first Lambda particle discovered was Λ0
in 1947 during a study of cosmic ray interactions.[2] Though the particle was expected to live for ~10−23 seconds,[2] it actually survived for ~10−10 seconds.[3] The property which caused it to live so long was dubbed strangeness, and led to the discovery of the strange quark.[2] Furthermore, these discoveries led to a principle known as the conservation of strangeness, wherein lightweight particles do not decay as quickly if they exhibit strangeness (because non-weak methods of particle decay must preserve the strangeness of the decaying baryon).[2]



The symbols encountered in this lists are: I (isospin), J (total angular momentum), P (parity), Q (charge), S (strangeness), C (charmness), B′ (bottomness), T (topness), B (baryon number), u (up quark), d (down quark), s (strange quark), c (charm quark), b (bottom quark), t (top quark), as well as other subatomic particles (hover for name).

Antiparticles are not listed in the table; however, they simply would have all quarks changed to antiquarks, and Q, B, S, C, B′, T, would be of opposite signs. I, J, and P values in red have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements.[4][5] The top lambda (Λ+
) is listed for completion's sake, but is not expected to be observed as top quarks decay before they have time to hadronize.[6]

Lambda baryons
Particle name Symbol Quark
Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to
Lambda[3] Λ0
uds 1,115.683±0.006 0 12+ 0 −1 0 0 0 2.631±0.020×10−10 p+
+ π

+ π0
charmed Lambda[7] Λ+
udc 2286.46|0.14}} 0 12 + +1 0 +1 0 0 2.00±0.06×10−13 See Λ+
decay modes
bottom Lambda[8] Λ0
udb 5,620.2±1.6 0 12 + 0 0 0 −1 0 1.409+0.055
See Λ0
decay modes
top Lambda Λ+
udt 0 12 + +1 0 0 0 +1

^ Particle unobserved, as the top-quark decays before it hadronizes.

See also


  1. ^ A. Quadt (2006). "Top quark physics at hadron colliders". European Physical Journal C 48 (3): 835–1000. Bibcode 2006EPJC...48..835Q. doi:10.1140/epjc/s2006-02631-6. 
  2. ^ a b c d The Strange Quark
  3. ^ a b C. Amsler et al. (2008): Particle listings – Λ
  4. ^ C. Amsler et al. (2008): Particle summary tables - Baryons
  5. ^ J. G. Körner et al. (1994)
  6. ^ Ho-Kim, Quang; Pham, Xuan Yem (1998). "Quarks and SU(3) Symmetry". Elementary Particles and Their Interactions: Concepts and Phenomena. Berlin: Springer-Verlag. p. 262. ISBN 3-540-63667-6. OCLC 38965994. "Because the top quark decays before it can be hadronized, there are no bound t anti-t states and no top-flavored mesons or baryons[...]." 
  7. ^ C. Amsler et al. (2008): Particle listings – Λ
  8. ^ C. Amsler et al. (2008): Particle listings – Λ


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