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 closely related Δ baryons exist: (constituent quarks: uuu), (uud), (udd), and (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 , a spin of , and an isospin of . Ordinary protons and neutrons (nucleons (symbol N)), by contrast, have a mass of about , a spin of , and an isospin of . The (uud) and (udd) particles are higher-mass excitations of the proton (, uud) and neutron (, udd), respectively. However, the and have no direct nucleon analogues.

The states were established experimentally at the University of Chicago cyclotron and the Carnegie Institute of Technology synchro-cyclotron in the mid-1950s using accelerated positive pions on hydrogen targets. The existence of the , with its unusual +2 charge, was a crucial clue in the development of the quark model.

The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher masses, additional Delta states appear, all defined by having units of isospin, but with a spin quantum numbers including , , , ... . A complete listing of all properties of all these states can be found in Beringer et al. (2013).

There also exist antiparticle Delta states with opposite charges, made up of the corresponding antiquarks.
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