# I Decay process as 1 to n

1. Dec 7, 2016

### spaghetti3451

Decay processes are quite common in particle physics.

Is the decay process always a $1 \rightarrow n$ process?

In other words, can we call the reaction $$\mu^{-} + \mu^{+} \rightarrow \phi,$$

where $\phi$ is some scalar particle, the decay of the muon?

2. Dec 7, 2016

3. Dec 7, 2016

### spaghetti3451

Can we have the incoming particle also in the set of outgoing particles?

4. Dec 7, 2016

### Staff: Mentor

That would violate energy/momentum conservation.

5. Dec 7, 2016

### stoomart

I believe this would require an intermediate stage, plus an external energy source. Consider neutron → proton → neutron transformation through beta decay:

β decay: when a free neutron decays into a proton

n → p + e + -νe

β+ decay: when a proton inside a nucleus decays into a neutron

p → n + e+ + νe

Note:

6. Dec 8, 2016

### ChrisVer

you call it annihilation of muon-antimuon...
obviously you don't have 1 muon to call it decay of the muon.
Can you have the incoming particle also in the outgoing particles? In vacuum as already mentioned no... but in other cases, yes, like Brehmstralung $e \rightarrow e \gamma$.

7. Dec 8, 2016

### stoomart

Since the charged particle is only losing kinetic energy and its invariant mass remains unchanged, is this really considered decay?

8. Dec 8, 2016

### ChrisVer

I didn't call it a decay- I gave that as an example to that you can have the same incoming and outgoing particle.

9. Dec 9, 2016

### vanhees71

Of course bremsstrahlung is not a decay process since you always need the electron to scatter with something since a free electron won't radiate. Only accelerated charges radiate. So the correct bremsstrahlung process is a scattering process like $\mathrm{e}^-+X \rightarrow \mathrm{e}^- + X +\gamma$, where $X$ is some particle or atomic nucleus scattering with the electron.