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++ 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 states were established experimentally at the University of Chicago cyclotron[2][3] and the Carnegie Institute of Technology synchro-cyclotron[4] in the mid-1950s using accelerated positive pions on hydrogen targets.
The existence of the Δ++, with its unusual electric charge of +2 e, was a crucial clue in the development of the quark model.
All of the Δ baryons with mass near 1232 MeV quickly decay via the strong interaction into a nucleon (proton or neutron) and a pion of appropriate charge.
The relative probabilities of allowed final charge states are given by their respective isospin couplings.