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]

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]

Lambda baryons

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	2286.46|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.

See also

Physics portal

• List of baryons

References

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
   c
8. ^ C. Amsler et al. (2008): Particle listings – Λ
   b

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.