ABSTRACT
Remembering the equivalence between mass and energy, we can describe the excited state as having a mass greater than that of the proton. is state was given the name delta (represented by the Greek letter Δ0), and the mass was about 1.3 times the proton mass. For the rst experiments using negative pions the delta was neutral; thus, you might call it an excited state of the neutron. A resonance with practically the same mass was found using positive pions, thus producing a doubly charged delta (Δ++). Further experiments with scattering from neutrons discovered two other charged states: delta plus (Δ+) and delta minus (Δ-).
