Delta baryon

The Delta baryons (or Δ baryons, also called Delta resonances) are a family of subatomic particle made of three up and/or down quarks, the same constituent quarks that make up the more familiar protons and neutrons.

Properties

Four closely related 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; their third component of isospin

I

3

=

±

1

2

o

r

±

3

2

;

{\displaystyle \;I_{3}=\pm {\tfrac {1}{2}}~{\mathsf {or}}~\pm {\tfrac {3}{2}}\;;}

and they are required to have an intrinsic spin of ⁠ 3 /2⁠ or higher (half-integer units). Ordinary nucleons (symbol N, meaning either a proton or neutron), by contrast, have a mass of about 939 MeV/c2, and both intrinsic spin and isospin of ⁠1/ 2 ⁠. The Δ+ (uud) and Δ0 (udd) particles are higher-mass spin-excitations of the proton (N+, uud) and neutron (N0, udd), respectively. The Δ++ and Δ−, however, have no direct nucleon analogues: For example, even though their charges are identical and their masses are similar, the Δ− (ddd), is not closely related to the antiproton (p, uud).

The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher spins, additional higher mass Delta states appear, all defined by having constant ⁠ 3 /2⁠ or ⁠ 1 /2⁠ isospin (depending on charge), but with spin ⁠ 3 /2⁠, ⁠ 5 /2⁠, ⁠ 7 /2⁠, ..., ⁠ 11 /2⁠ multiplied by ħ. A complete listing of all properties of all these states can be found in Beringer et al. (2013).