Lambda baryon


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

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 12+ 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 12 + +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 12 + 0 0 0 −1 0 1.409+0.055
−0.054
×10−12
See Λ0
b
decay modes
top Lambda Λ+
t
udt 0 12 + +1 0 0 0 +1

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

See also

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


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • lambda baryon — noun Any of three particles, having no electric charge and an isotopic spin of 1, composed of an up quark, down quark and either a strange quark, a charm quark or a bottom quark Syn: lambda hyperon, lambda particle …   Wiktionary

  • lambda hyperon — noun lambda baryon …   Wiktionary

  • lambda particle — noun lambda baryon …   Wiktionary

  • Baryon lambda — En physique des particules, un baryon lambda, noté par la lettre grecque Λ, est un baryon instable non chargé, constitué de trois quarks : un quark up, un quark down et un quark bottom (c est alors un baryon Λ0b), charm (Λ+c) ou strange (Λ0) …   Wikipédia en Français

  • Baryon sigma — Les baryons Sigma (aussi appelés particules Sigma) sont des baryons composés d un quark étrange (dit quark s) et d une combinaison de quarks up et down, le tout possédant un isospin de 1. Les baryons sigma sont des hypérons. Ils sont notés avec… …   Wikipédia en Français

  • Lambda-CDM model — Physical cosmology Universe · Big Bang …   Wikipedia

  • Baryon — Baryons are the family of subatomic particles with a baryon number of 1. The term baryon is usually used to refer to triquarks baryons made of three quarks. Exotic baryons made of four quarks and one antiquark are known as the pentaquarks, but… …   Wikipedia

  • Baryon Lambda — En physique des particules, un baryon lambda, noté par la lettre grecque Λ, est un baryon instable non chargé, constitué de trois quarks : un up, un down et soit un bottom (c est alors un baryon Λ0b), soit un charm (baryon Λ+c), soit un… …   Wikipédia en Français

  • Baryon — Les huit baryons de spin 1/2 composés uniquement de quarks u, d et s, classés par étrangeté (S) et charge (Q) Un baryon est, en physique des particules, une catégorie de particules, dont les représentants les plus connus sont le proton et le… …   Wikipédia en Français

  • Baryon — Baryonen (von altgriechisch βαρύς barýs ‚schwer‘, ‚gewichtig‘)[1] sind stark wechselwirkende Elementarteilchen (also Hadronen) mit halbzahligem Spin (d. h. Fermionen). Baryonen bestehen aus jeweils drei Quarks (bzw. Antibaryonen aus jeweils… …   Deutsch Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.