Provided they aren't in an excited state (which would allow a decay via EM or strong). I had a question asking why the neutral lambda particle, consisting of uds quarks, has a lifetime characteristic of the weak. The answer being that it must decay via the weak to change the s-quark flavour in to a down or an up. But this has me thinking, don't all baryons decay only by the weak force? I don't have it confirmed in my notes anywhere, and a google search revealed to me that most baryons do (but didn't mention why there was an exception). If a decay process must happen through the constraint that the constiuent produced particles have less rest mass-energy than the decaying particle, then surely weak is the only way? Because a strong decay (emission of a gluon by a quark) or a electromagnetic decay (emission of a photon) of a hadron (consititing of only three quarks, no antiquarks) can only hope to pair-produce more quarks but not change any of the quarks of the original hadron. Hence increasing mass-energy, rather than lowering, contradicting the original assumption. So a baryon can only reduce the rest mass-energy by the weak force, the strong/EM just increase it for a baryon. Surely? It seems like something that should've been mentioned if it was true. Maybe I'm over-simplifying the decay process (and there isn't something I've considered). Case isn't the same for a meson of course. The neutral pion can self annihilate and decay into two photons via the EM force.