| Composition |
|
|---|---|
| Statistics | Fermionic |
| Family | Baryons |
| Interactions | Strong,weak,electromagnetic, andgravity |
| Types | 3 |
| Mass | |
| Spin | 1⁄2 |
| Strangeness | -1 |
| Isospin | 1 |
Thesigma baryons are a family ofsubatomichadron particles which have twoquarks from the firstflavour generation (up and / ordown quarks), and a third quark from a higher flavour generation, in a combination where the wavefunction sign remains constant when any two quark flavours are swapped. They are thusbaryons, with totalisospin of 1, and can either beneutral or have anelementary charge of +2, +1, 0, or −1. They are closely related to thelambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.
The third quark can hence be either astrange (symbols
Σ+
,
Σ0
,
Σ−
), acharm (symbols
Σ++
c,
Σ+
c,
Σ0
c), abottom (symbols
Σ+
b,
Σ0
b,
Σ−
b) or atop (symbols
Σ++
t,
Σ+
t,
Σ0
t) quark. However, the top sigmas are expected to never be observed, since theStandard Model predicts themean lifetime of top quarks to be roughly5×10−25 s.[2] This is about 20 times shorter than the timescale forstrong interactions, and therefore it does notform hadrons.
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), andQ,B,S,C,B′,T, would be of opposite signs.I,J, andP values in red have not been firmly established by experiments, but are predicted by thequark model and are consistent with the measurements.[3][4]
| Particle name | Symbol | Quark content | Rest mass (MeV/c2) | I | JP | Q (e) | S | C | B′ | T | Mean lifetime (s) | Decay modes (branching ratio) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sigma[5] | 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 ((51.57±0.30)%) n0 + π+ ((48.31±0.30)%) |
| 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 (100%) |
| Sigma[5] | 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− ((99.848±0.005)%) |
| Charmed sigma[5] | Σ++ c(2455) | u u c | 2,453.97 ± 0.14 | 1 | 1/2 + | +2 | 0 | +1 | 0 | 0 | 3.5 ± 0.4 × 10−22[a] | Λ+ c + π+ (≈100%) |
| Charmed sigma[5] | 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 (≈100%) |
| Charmed sigma[5] | Σ0 c(2455) | d d c | 2,453.75 ± 0.14 | 1 | 1/2 + | 0 | 0 | +1 | 0 | 0 | 3.6± 0.4 × 10−22[a] | Λ+ c + π− (≈100%) |
| Bottom sigma[5] | Σ+ b | u u b | 5,810.56 ± 0.23 | 1 | 1/2 + | +1 | 0 | 0 | −1 | 0 | 1.31± 0.13 × 10−22[a] | Λ0 b + π+ (dominant) |
| Bottom sigma† | Σ0 b | u d b | Unknown | 1 | 1/2 + | 0 | 0 | 0 | −1 | 0 | Unknown | Unknown |
| Bottom sigma[5] | Σ− b | d d b | 5,815.2 ± 0.27 | 1 | 1/2 + | −1 | 0 | 0 | −1 | 0 | 1.24± 0.13 × 10−22[a] | Λ0 b + π− (dominant) |
| 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.
[a]^PDG reports theresonance width (Γ). Here the conversionτ = 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).
| Particle name | Symbol | Quark content | Rest mass (MeV/c2) | I | JP | Q (e) | S | C | B′ | T | Mean lifetime (s) | Commonly decays to |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sigma[6] | 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[6] | 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 Σ− + π+ |
| Sigma[6] | 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[7] | 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[7] | 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[7] | 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.
[c]^PDG reports the resonance width (Γ). Here the conversionτ = ħ/Γ is given instead.
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