Whys and Hows of Particle Decay

why some particles decay quickly and some take very long time to decay? What determines the decay probability and lifespan of particle? and via what mechanism does it affect the probability/lifespan?
- anon (age ?)

Dear anon,

The rate of particle decay depends on several things:

1. Conservation laws.   For example an electron cannot decay into a neutrino and a photon because charge would not be conserved.   Likewise angular momentum, baryon number, lepton number, and energy must be conserved.

2. Strength of interaction.  In decreasing order one has nuclear forces, electromagnetic forces, and weak interactions.   For example alpha emission from nucleii in the first case,  photon emission from an excited state of an atom in the second , and beta decay of a nucleus or decay of a muon into an electron plus neutrinos in the case of the weak interactions.  The force of gravity is simply too weak to be considered in particle decay. 

3. Finally there is a factor called phase-space that accounts for the availability of final states to accomodate the newly formed system.   This typically grows as the momenta of the final state particles.

 

LeeH

(published on 10/30/2013)