Decay Modes of J/psi: Understanding Gamma and Hadron Decays

Everywhere I look, I see the claim that J/psi decays to "g g g" about 64% of the time, and to "gamma -----> hadrons" about 13% of the time.

My question is, exactly how does one distinguish between (1) J/psi -----> g g g ------> hadrons, and (2) J/psi -----> gamma ------> hadrons?

If you observe J/psi -----> hadrons in the lab, is there never a case where this could be a result of either (or even quantum interference of the two)?

How does one interpret a decay like J/psi -----> p pbar as one or the other?

nightvidcole said:

TL;DR Summary: Is there always a unique signature of J/psi -----> g g g ?

My question is, exactly how does one distinguish between (1) J/psi -----> g g g ------> hadrons, and (2) J/psi -----> gamma ------> hadrons?

You can't. In QM you add amplitudes and then square. You can't tell from a final state what the intermediate state was (and the question doesn't even make sense).

What you can do is say that given that the branching fraction to electrons is 6%, and the branching fraction to muons is 6%, if decays to quarks were purely electromagnetic, that would be 3(4/9 + 1/9 + 1/9) x 6% = 12%, so the remainder is gluon-induced. Maybe not strictly true, but it give you an idea of the relative magnitudes.

nightvidcole said:

TL;DR Summary: Is there always a unique signature of J/psi -----> g g g ?

How does one interpret a decay like J/psi -----> p pbar as one or the other?

That decay is almost purely QCD.

[itex]B(J/\psi \rightarrow p\overline{p})
\approx B(J/\psi \rightarrow n\overline{n} )[/itex]

You would expect the proton channel to dominate if the decay were primarily electromagnetic.