What was the first discovery of the delta baryon $\Delta^{++}$?

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.

1. i want first reference claims delta baryon discovery

2. why the mass of all delta particles are the same!?

3. proton and neutron quarks content are the same with $\Delta^{+}$, $\Delta^{0}$, So why they have so different mass!?

-
The second subquestion(v2) is essentially a duplicate of physics.stackexchange.com/q/20999/2451 – Qmechanic Sep 20 '12 at 14:40
The fun part of trying to run down the first observation is that it will almost certainly not use the same language to describe the thing that we use today. BTW--on the matter of vocabulary "subatomic hadron particles" is redundant two ways: all hadrons are particles and they are all subatomic. – dmckee Sep 20 '12 at 15:16