Sigma baryon

The Sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation (up and/or down quarks), and a third quark from higher flavour generations, in a combination where the wavefunction does not swap sign when any two quark flavours are swapped. They are thus baryons, with Total Isospin of 1, and can either be neutral or have an elementary charge of +2, +1 or −1. They are closely related to the Lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.

The third quark can hence be either a strange (symbols
Σ+
,
Σ0
,
Σ−
), a charm (symbols
Σ++
c,
Σ+
c,
Σ0
c), a bottom (symbols
Σ+
b,
Σ0
b,
Σ−
b) or a top (symbols
Σ++
t,
Σ+
t,
Σ0
t) quark. However, the top Sigmas are 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.

List

The symbols encountered in these lists are: I (isospin), J (total angular momentum), P (parity), u (up quark), d (down quark), s (strange quark), c (charm quark), t (top quark), b (bottom quark), Q (electric charge), S (strangeness), C (charmness), B′ (bottomness), T (topness), 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 vice versa), 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.[2][3]

JP = 1/2+ Sigma baryons

JP = 1/2+ Sigma baryons
Particle name Symbol Quark
content		 Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to
Sigma[4]
Σ+
u

u

s
 1,189.37 ± 0.07 1 1/2+ +1 −1 0 0 0 8.018 ± 0.026 × 10−11
p+
 +
π0
 or


n0
 +
π+

Sigma[5]
Σ0
u

d

s
 1,192.642 ± 0.024 1 1/2+ 0 −1 0 0 0 7.4 ± 0.7 × 10−20
Λ0
 +
γ
Sigma[6]
Σ−
d

d

s
 1,197.449 ± 0.030 1 1/2+ −1 −1 0 0 0 1.479 ± 0.011 × 10−10
n0
 +
π−
charmed Sigma[7]
Σ++
c(2455)
u

u

c
 2,454.02 ± 0.18 1 1/2 + +2 0 +1 0 0 3.0 ± 0.4 × 10−22[a]
Λ+
c +
π+
charmed Sigma[7]
Σ+
c(2455)
u

d

c
 2,452.9 ± 0.4 1 1/2 + +1 0 +1 0 0 >1.4 × 10−22[a]
Λ+
c +
π0
charmed Sigma[7]
Σ0
c(2455)
d

d

c
 2,453.76 ± 0.18 1 1/2 + 0 0 +1 0 0 3.0 ± 0.5 × 10−22[a]
Λ+
c +
π−
bottom Sigma[8]
Σ+
b
u

u

b
 5,807.7 ± 3.8 1 1/2 + +1 0 0 −1 0 Unknown
Λ0
b +
π+
 (seen)
bottom Sigma†
Σ0
b
u

d

b
 Unknown 1 1/2 + 0 0 0 −1 0 Unknown Unknown
bottom Sigma[8]
Σ−
b
d

d

b
 5,815.2 ± 2.7 1 1/2 + −1 0 0 −1 0 Unknown
Λ0
b +
π−
 (seen)
Top Sigma†
Σ++
t
u

u

t
 — 1 1/2 + +2 0 0 0 +1 — —
Top Sigma†
Σ+
t
u

d

t
 — 1 1/2 + +1 0 0 0 +1 — —
Top Sigma†
Σ0
t
d

d

t
 — 1 1/2 + 0 0 0 0 +1 — —

† ^ The standard model predicts that this particle cannot exist due to the short lifetime of the top quark.
[a] ^ PDG reports the resonance width (Γ). Here the conversion τ = ħ/Γ is given instead.
[b] ^ The specific values of the name has not been decided yet, but will likely be close to
Σ
b(5810).

JP = 3/2+ Sigma baryons

JP = 3/2+ Sigma baryons
Particle name Symbol Quark
content		 Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to
Sigma[9]
Σ∗+
(1385)
u

u

s
 1,382.8 ± 0.4 1 3/2+ +1 −1 0 0 0 1.84 ± 0.04 × 10−23[c]
Λ0
 +
π+
 or


Σ+
 +
π0
 or

Σ0
 +
π+

Sigma[9]
Σ∗0
(1385)
u

d

s
 1,383.7 ± 1.0 1 3/2+ 0 −1 0 0 0 1.8 ± 0.3 × 10−23[c]
Λ0
 +
π0
 or


Σ+
 +
π−
 or

Σ0
 +
π0

Sigma[9]
Σ∗−
(1385)
d

d

s
 1,387.2 ± 0.5 1 3/2+ −1 −1 0 0 0 1.67 ± 0.09 × 10−23[c]
Λ0
 +
π−
 or


Σ0
 +
π−
 or

Σ−
 +
π0
 or

charmed Sigma[10]
Σ∗++
c(2520)
u

u

c
 2,518.4 ± 0.6 1 3/2 + +2 0 +1 0 0 4.4 ± 0.6 × 10−23[c]
Λ+
c +
π+
charmed Sigma[10]
Σ∗+
c(2520)
u

d

c
 2,517.5 ± 2.3 1 3/2 + +1 0 +1 0 0 >3.9 × 10−23[c]
Λ+
c +
π0
charmed Sigma[10]
Σ∗0
c(2520)
d

d

c
 2,518.0 ± 0.5 1 3/2 + 0 0 +1 0 0 4.1 ± 0.5 × 10−23[c]
Λ+
c +
π−
bottom Sigma†
Σ∗+
b
u

u

b
 Unknown 1 3/2 + +1 0 0 −1 0 Unknown Unknown
bottom Sigma†
Σ∗0
b
u

d

b
 Unknown 1 3/2 + 0 0 0 −1 0 Unknown Unknown
bottom Sigma†
Σ∗−
b
d

d

b
 Unknown 1 3/2 + −1 0 0 −1 0 Unknown Unknown
Top Sigma†
Σ∗++
t
u

u

t
 — 1 3/2 + +2 0 0 0 +1 — —
Top Sigma†
Σ∗+
t
u

d

t
 — 1 3/2 + +1 0 0 0 +1 — —
Top Sigma†
Σ∗0
t
d

d

t
 — 1 3/2 + 0 0 0 0 +1 — —

† ^ The standard model predicts that this particle cannot exist due to the short lifetime of the top quark.
[c] ^ PDG reports the resonance width (Γ). Here the conversion τ = ħ/Γ is given instead.

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. ↑ C. Amsler et al. (2008): Particle summary tables – Baryons
  3. ↑ J. G. Körner et al. (1994)
  4. ↑ C. Amsler et al. (2008): Particle listings –
    Σ+
  5. ↑ C. Amsler et al. (2008): Particle listings –
    Σ0
  6. ↑ C. Amsler et al. (2008): Particle listings –
    Σ−
  7. 1 2 3 C. Amsler et al. (2008): Particle listings –
    Σ
    c    (2455)
  8. 1 2 T. Aaltonen et al. (2007a)
  9. 1 2 3 C. Amsler et al. (2008): Particle listings –
    Σ
    (1385)
  10. 1 2 3 C. Amsler et al. (2008): Particle listings –
    Σ
    c    (2520)

Bibliography

  • C. Amsler et al. (Particle Data Group) (2008). "Review of Particle Physics". Physics Letters B. 667 (1): 1. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018.
  • J. G. Körner; M. Krämer & 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.
  • T. Aaltonen et al. (CDF Collaboration) (2007a). "First Observation of Heavy Baryons
    Σ
    b     and
    Σ∗
    b    ". Physical Review Letters. 99 (20): 202001. arXiv:0706.3868. Bibcode:2007PhRvL..99t2001A. doi:10.1103/PhysRevLett.99.202001.
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