Physics:Sigma baryon

Short description: Baryon made of specific quark combinations

Sigma baryon

Composition	Σ+: uus Σ0: uds Σ−: dds
Statistics	Fermionic
Interactions	Strong, weak, electromagnetic, and gravity
Types	3
Mass	Σ+: 1189.37±0.07 MeV/c2 Σ0: 1192.642±0.024 MeV/c2 Σ−: 1197.449±0.030 MeV/c2
Spin	​1⁄2
Strangeness	-1
Isospin	1

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 a higher flavour generation, in a combination where the wavefunction sign remains constant 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, 0, 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, Σ0c), a bottom (symbols Σ+b, Σ0b, Σ−b) or a top (symbols Σ++t, Σ+t, Σ0t) quark. However, the top sigmas are expected to never be observed, since the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10⁻²⁵ s. 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.

J^P = 1/2⁺ sigma baryons

J^P = 1/2⁺ sigma baryons

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	Σ+	Up quarkUp quarkStrange quark	1,189.37 ± 0.07	1	1/2+	+1	−1	0	0	0	8.018 ± 0.026 × 10−11	Proton+ + Pion0 ((51.57±0.30)%) Neutron0 + Pion+((48.31±0.30)%)
Sigma	Σ0	Up quarkDown quarkStrange quark	1,192.642 ± 0.024	1	1/2+	0	−1	0	0	0	7.4 ± 0.7 × 10−20	Lambda0 + Photon (100%)
Sigma	Σ−	Down quarkDown quarkStrange quark	1,197.449 ± 0.030	1	1/2+	−1	−1	0	0	0	1.479 ± 0.011 × 10−10	Neutron0 + Pion- ((99.848±0.005)%)
Charmed sigma	Σ++c(2455)	Up quarkUp quarkCharm quark	2,453.97 ± 0.14	1	1/2 +	+2	0	+1	0	0	3.5 ± 0.4 × 10−22	Λ+c + Pion+(≈100%)
Charmed sigma	Σ+c(2455)	Up quarkDown quarkCharm quark	2,452.9 ± 0.4	1	1/2 +	+1	0	+1	0	0	>1.4 × 10−22	Λ+c + Pion0 (≈100%)
Charmed sigma	Σ0c(2455)	Down quarkDown quarkCharm quark	2,453.75 ± 0.14	1	1/2 +	0	0	+1	0	0	3.6± 0.4 × 10−22	Λ+c + Pion- (≈100%)
Bottom sigma	Σ+b	Up quarkUp quarkb	5,810.56 ± 0.23	1	1/2 +	+1	0	0	−1	0	1.31± 0.13 × 10−22	Bottom Lambda0 + Pion+ (dominant)
Bottom sigma	Σ0b	Up quarkDown quarkb	Unknown	1	1/2 +	0	0	0	−1	0	Unknown	Unknown
Bottom sigma	Σ−b	Down quarkDown quarkb	5,815.2 ± 0.27	1	1/2 +	−1	0	0	−1	0	1.24± 0.13 × 10−22	Λ0b + Pion- (dominant)
Top sigma	Σ++t	Up quarkUp quarkTop quark	—	1	1/2 +	+2	0	0	0	+1	—	—
Top Sigma	Σ+t	Up quarkDown quarkTop quark	—	1	1/2 +	+1	0	0	0	+1	—	—
Top Sigma	Σ0t	Down quarkDown quarkTop quark	—	1	1/2 +	0	0	0	0	+1	—	—

^† ^ The standard model predicts that this particle cannot exist.
^[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).

J^P = 3/2⁺ sigma baryons

J^P = 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	Σ∗+(1385)	Up quarkUp quarkStrange quark	1,382.8 ± 0.4	1	3/2+	+1	−1	0	0	0	1.84 ± 0.04 × 10−23	Lambda0 + Pion+ or Σ+ + Pion0 or Σ0 + Pion+
Sigma	Σ∗0(1385)	Up quarkDown quarkStrange quark	1,383.7 ± 1.0	1	3/2+	0	−1	0	0	0	1.8 ± 0.3 × 10−23	Lambda0 + Pion0 or Σ+ + Pion- or Σ− + Pion+
Sigma	Σ∗−(1385)	Down quarkDown quarkStrange quark	1,387.2 ± 0.5	1	3/2+	−1	−1	0	0	0	1.67 ± 0.09 × 10−23	Lambda0 + Pion- or Σ0 + Pion- or Σ− + Pion0 or
Charmed sigma	Σ∗++c(2520)	Up quarkUp quarkCharm quark	2,518.4 ± 0.6	1	3/2 +	+2	0	+1	0	0	4.4 ± 0.6 × 10−23	Charmed Lambda+ + Pion+
Charmed sigma	Σ∗+c(2520)	Up quarkDown quarkCharm quark	2,517.5 ± 2.3	1	3/2 +	+1	0	+1	0	0	>3.9 × 10−23	Charmed Lambda+ + Pion0
Charmed sigma	Σ∗0c(2520)	Down quarkDown quarkCharm quark	2,518.0 ± 0.5	1	3/2 +	0	0	+1	0	0	4.1 ± 0.5 × 10−23	Charmed Lambda+ + Pion-
Bottom sigma	Σ∗+b	Up quarkUp quarkb	Unknown	1	3/2 +	+1	0	0	−1	0	Unknown	Unknown
Bottom sigma	Σ∗0b	Up quarkDown quarkb	Unknown	1	3/2 +	0	0	0	−1	0	Unknown	Unknown
Bottom sigma	Σ∗−b	Down quarkDown quarkb	Unknown	1	3/2 +	−1	0	0	−1	0	Unknown	Unknown
Top sigma	Σ∗++t	Up quarkUp quarkTop quark	—	1	3/2 +	+2	0	0	0	+1	—	—
Top sigma	Σ∗+t	Up quarkDown quarkTop quark	—	1	3/2 +	+1	0	0	0	+1	—	—
Top sigma	Σ∗0t	Down quarkDown quarkTop quark	—	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 conversion τ = ħ/Γ is given instead.

See also

• Delta baryon
• Hyperon
• Lambda baryon
• List of mesons
• List of particles
• Nucleon
• Omega baryon
• Physics portal
• Timeline of particle discoveries
• Xi baryon

Bibliography

• Amsler, C. (2008). "Review of Particle Physics". Physics Letters B 667 (1): 1. doi:10.1016/j.physletb.2008.07.018. Bibcode: 2008PhLB..667....1A. http://scipp.ucsc.edu/%7Ehaber/pubs/Review_of_Particle_Physics_2014.pdf. 
• Körner, J.G.; Krämer, M.; Pirjol, D. (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics 33: 787–868. doi:10.1016/0146-6410(94)90053-1. Bibcode: 1994PrPNP..33..787K. 
• Aaltonen, T. (2007). "First Observation of Heavy Baryons Σ_b and Σ∗b". Physical Review Letters 99 (20): 202001. doi:10.1103/PhysRevLett.99.202001. PMID 18233134. Bibcode: 2007PhRvL..99t2001A. https://digital.csic.es/bitstream/10261/8529/2/e202001.pdf.