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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!?

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The second subquestion(v2) is essentially a duplicate of –  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

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You may find useful this paper from the particle data group listings:N AND Delta RESONANCES . It gives a concise explanation and references of what the resonances are. You may chase the original references there.

There are many Delta resonances as you can see in the table, with different masses. It is only within each isospin multiplet of mass that the mass is the same. The are named N resonances if the isospin is 1/2 ( nucleon like) and delta, if it is 3/2.

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