Is there a way to compute or explain if a decay prefers decaying into mainly mass or mainly energy?

Is there a way to compute or explain if a decay prefers decaying into mainly mass or mainly energy ? I know quarks prefer to decay into the most massfull quarks : http://hyperphysics.phy-astr.gsu.edu/hbase/particles/qrkdec.html

And emitting photons is a (or partially is) a massless decay.

I only know E = gamma mc^2 from relativity must hold and the things must be expressable in quanta (so no irrational energy/mass ratio or such).

Plz not all complicated answers , im no expert in QM.

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 This question cannot be answered simply. Quark decays are controlled by a specific matrix, fixed by experimental measurements en.wikipedia.org/wiki/… ; it is crucial for the Standard Model. All other particle weak decays (for example neutron decay) end up being the decay of some quark and there are mathematical formulae that one can use to calculate the decay rates. In general there are rules of how quantum numbers are conserved or change. It is not as simple as "mainly mass or mainly energy". – anna v Oct 22 '12 at 17:03