Delta baryon
The Delta baryons (or Δ baryons, also called Delta resonances) are a family of subatomic particle made of three up or down quarks (u or d quarks).
Four Δ baryons exist: Δ++ (constituent quarks: uuu), Δ+ (uud), Δ0 (udd), and Δ− (ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e.
The Δ baryons have a mass of about 1232 MeV/c2, a spin of 3⁄2, and an isospin of 3⁄2. In many ways, Δ baryons are 'excited' nucleon (symbol N), which are made of the same constituent quarks in a lower-energy spin configuration (spin 1⁄2). The Δ+ (uud), Δ0 (udd) are the higher-energy equivalent of the proton (N+, uud) and neutron (N0, udd). However, the Δ++ and Δ− have no nucleon equivalent.
Composition
The four Δ baryons are distinguished by their electrical charges, which is the sum of the charges of the quarks from which they are composed. There are also four antiparticles with opposite charges, made up of the corresponding antiquarks. The existence of the Δ++, with its unusual +2 charge, was a crucial clue in the development of the quark model.
Decay
All varieties of Δ baryons quickly decay via the strong force into a nucleon (proton or neutron) and a pion of appropriate charge. The amplitudes of various final charge states given by their respective isospin couplings. More rarely and more slowly, the Δ+ can decay into a proton and a photon and the Δ0 can decay into a neutron and a photon.
List
| Particle name | Symbol | Quark content |
Rest mass (MeV/c2) | I3 | JP | Q (e) | S | C | B′ | T | Mean lifetime (s) | Commonly decays to |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Delta[1] | Δ++(1232) | uuu | 1,232 ± 2 | +3⁄2 | 3⁄2+ | +2 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | p+ + π+ |
| Delta[1] | Δ+(1232) | uud | 1,232 ± 2 | +1⁄2 | 3⁄2+ | +1 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π+ + n0 or |
| Delta[1] | Δ0(1232) | udd | 1,232 ± 2 | −1⁄2 | 3⁄2+ | 0 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π0 + n0 or |
| Delta[1] | Δ−(1232) | ddd | 1,232 ± 2 | −3⁄2 | 3⁄2+ | −1 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π− + n0 |
[a] ^ PDG reports the resonance width (Γ). Here the conversion τ = ℏ/Γ is given instead.
References
- 1 2 3 4 J. Beringer et al. (2013): Particle listings – Δ(1232)
Bibliography
- C. Amsler et al. (Particle Data Group) (2008). "Review of Particle Physics". Physics Letters B 667 (1): 1. Bibcode:2008PhLB..667....1P. doi:10.1016/j.physletb.2008.07.018.
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