# Why does the proton have no excited states?

1. Sep 24, 2011

### petergreat

I've never heard of any excited states of the proton. Why?
By "excited state" I mean something with the same composition (uud) that decays to the proton (plus photons etc.) with nearly 100% branching ratio.

2. Sep 24, 2011

### Staff: Mentor

3. Sep 24, 2011

### petergreat

Thanks! One question, though. Does the $\Delta^+$ decay to $p\pi^0$ or to $n\pi^+$ more often? According to Wikipedia on Delta baryons both decay modes exist.

4. Sep 25, 2011

### Staff: Mentor

In order to answer that question, I'd go to the Particle Data Group and search through the baryon tables, but you might as well do it yourself.

http://pdg.lbl.gov/

5. Sep 25, 2011

### petergreat

I actually check PDG before I posted the previous reply, but I got lost...
I went to Particle Properties -> Baryons, and found a list of reviews. I admit I often don't understand the terminology, but none of them seems to have any information on Delta+ branching ratios.

6. Sep 25, 2011

### Vanadium 50

Staff Emeritus
That's because the decays are given by Clebsch-Gordon coefficients and the assumption is anyone can calculate them.

7. Sep 25, 2011

### Bill_K

Last edited by a moderator: Apr 26, 2017
8. Sep 25, 2011

### Chronos

Neutrons decay into protons [plus electons and electron antineutrinos].

9. Sep 25, 2011

### Meir Achuz

The ratio of Delta-->pi0 n/Delta-->pi- p is determined by isospin to be 2:1.

10. Sep 25, 2011

### Meir Achuz

Thereare a large number of excited states of the proton besides the Delta.
All the states called N* or Delta can be considered excited states of the proton.
They decay mainly into pions and a proton or neutron.
There is a small branching ratio into photon and nucleon.

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