Question

what is particle Decay ?

Answer 1

Particle decay is the spontaneous process of one unstable subatomic particle transforming into multiple other particles. 

Answer 2

Particle decay is the spontaneous process of one unstable subatomic particle transforming into multiple other particles. ... Unstable particles will often have multiple ways of decaying, each with its own associated probability. Decays are mediated by one or several fundamental forces.