Lambda baryon
The Lambda baryons are a family of subatomic hadron particles which have the symbols Λ0
, Λ+
c, Λ0
b and Λ+
t 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+
c), a bottom (Λ0
b) or a top (Λ+
t) 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]
Contents |
[edit] List
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+
t) is listed for completion's sake, but is not expected to be observed as top quarks decay before they have time to hadronize.[6]
| Particle name | Symbol | Quark content |
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 | 1⁄2+ | 0 | −1 | 0 | 0 | 0 | 2.631±0.020×10−10 | p+ + π− or n0 + π0 |
| charmed Lambda[7] | Λ+ c |
udc | 2,286.46±0.14 | 0 | 1⁄2 + | +1 | 0 | +1 | 0 | 0 | 2.00±0.06×10−13 | See Λ+ c decay modes |
| bottom Lambda[8] | Λ0 b |
udb | 5,620.2±1.6 | 0 | 1⁄2 + | 0 | 0 | 0 | −1 | 0 | 1.409+0.055 −0.054×10−12 |
See Λ0 b decay modes |
| top Lambda† | Λ+ t |
udt | — | 0 | 1⁄2 + | +1 | 0 | 0 | 0 | +1 | — | — |
† ^ Particle unobserved, as the top-quark decays before it hadronizes.
[edit] See also
[edit] References
- ^ 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.
- ^ a b c d The Strange Quark
- ^ a b C. Amsler et al. (2008): Particle listings – Λ
- ^ C. Amsler et al. (2008): Particle summary tables - Baryons
- ^ J. G. Körner et al. (1994)
- ^ 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
states and no top-flavored mesons or baryons[...]." - ^ C. Amsler et al. (2008): Particle listings – Λ
c - ^ C. Amsler et al. (2008): Particle listings – Λ
b
states and no top-flavored mesons or baryons[...]."[edit] Bibliography
- C. Amsler et al. (Particle Data Group) (2008). "Review of Particle Physics". Physics Letters B 667: 1. Bibcode 2008PhLB..667....1P. doi:10.1016/j.physletb.2008.07.018.
- C. Caso et al. (Particle Data Group) (1998). "Review of Particle Physics". European Physical Journal C 3: 1. Bibcode 1998EPJC....3....1P. doi:10.1007/s10052-998-0104-x.
- J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics 33: 787–868. arXiv:hep-ph/9406359. Bibcode 1994PrPNP..33..787K. doi:10.1016/0146-6410(94)90053-1.
- R. Nave (12 April 2005). "The Lambda Baryon". HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lambda.html. Retrieved 2010-07-14.
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