# Homework Help: Elementary particle problems

1. Oct 13, 2014

### sudipmaity

1. The problem statement, all variables and given/known data
Indicate the fundamental interactions through which the following processes occur.Justify.
n -> p+ e- + -νe.....1
p+p -> p+p+n+-n.....2
π+ -> μ++ -νμ....3
γ -> e+ + e-.....4

2. Relevant equations

3. The attempt at a solution
1... is possible due to weak decay .electron antineutrino production.
2.... is possible due to baryon no. conservation.
3.... is not possible as lepton no. is not conserved.
4....is possible due to pair production and if energy of gamma rays is greater than 1.02MeV.It has been expermentally proven.
Are my deductions correct?? I am a particle, nuclear physics beginner.

2. Oct 13, 2014

### Orodruin

Staff Emeritus
Assuming that -ve means $\bar\nu_e$ etc. The first three are fine as long as the protons in (2) have enough CoM energy to create the neutron-antineutron pair.

For (4), it is not possible unless you can transfer momentum from an external field, such as that of a nearby nucleus. As it stands, you cannot conserve energy and momentum at the same time.

3. Oct 13, 2014

### vela

Staff Emeritus
You don't seem to be answering the question, which is to identify which interaction is responsible for each process.

For #2, I wouldn't say conservation of baryon number makes it possible. Conservation laws are generally used to rule out potential processes.

For #3, you need to recognize that the antineutrino has a lepton number of -1 because it's antimatter.

For #4, you need a second photon to be able to conserve momentum and energy. This second photon could be a virtual photon associated with the external field Orodruin mentions.

4. Oct 14, 2014

### sudipmaity

Thank you vela.Is my answer to to #1 correct??

5. Oct 14, 2014

### vela

Staff Emeritus
You tell me. Why do you think it's mediated by the weak interaction?