- Delta baryon
The Delta baryons (also called Delta resonances) are a family of subatomic hadron particles which have the symbols Δ++
, and Δ−
and electric charges +2, +1, 0 and -1 elementary charge respectively. They are relatively light (1,232 MeV/c2) baryons made of only up (u) and down (d) quarks which have spin and isospin 3⁄2, as opposed to nucleons (proton and neutron) which have spin and isospin 1⁄2.
The four different particles that make up the delta family are distinguished by their electrical charges, which is the sum of the charges of the mixture of up (u) and down (d) quarks of 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.
The 3⁄2 spin means that all the three quarks inside a Δ particle have their spin axis pointing in the same direction, unlike the nearly identical proton and neutron in which the intrinsic spin of one of the three constituent quarks is always opposite the spin of the other two. This spin alignment is complemented by an isospin quantum number of 3⁄2 which differentiates the Δ+
and ordinary nucleons, which have spin and isospin of 1⁄2.
All varieties of Δ 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.
Delta baryons Particle name Symbol Quark
Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to Delta Δ++
uuu 1,232 ± 1 3⁄2 3⁄2+ +2 0 0 0 0 5.58 ± 0.09 × 10−24[a] p+
uud 1,232 ± 1 3⁄2 3⁄2+ +1 0 0 0 0 5.58 ± 0.09 × 10−24[a] π+
udd 1,232 ± 1 3⁄2 3⁄2+ 0 0 0 0 0 5.58 ± 0.09 × 10−24[a] π0
ddd 1,232 ± 1 3⁄2 3⁄2+ −1 0 0 0 0 5.58 ± 0.09 × 10−24[a] π−
[a] ^ PDG reports the resonance width (Γ). Here the conversion τ = ħ⁄Γ is given instead.
- 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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