Why does the proton have no excited states?

[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.

[jtbell]

Consider the \Delta^{+}:

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/delta.html

[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.

[jtbell]

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. :wink:

http://pdg.lbl.gov/

[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.

[Vanadium 50]

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

[Bill_K]

Two-thirds p+ π0 and one-third n0 π+. See here (http://www.ippp.dur.ac.uk/~richardn/particles/particle.php?action=2214).

[Chronos]

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

[Meir Achuz]

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

[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.