The delta baryons (also called delta resonances) are a family of subatomic hadron particles which have the symbols $\Delta^{++}$, $\Delta^{+}$, $\Delta^{0}$, and $\Delta^{−}$ and electric charges +2, +1, 0 and −1 elementary charge respectively.
i want first reference claims delta baryon discovery
why the mass of all delta particles are the same!?
proton and neutron quarks content are the same with $\Delta^{+}$, $\Delta^{0}$, So why they have so different mass!?