# Charge non-conservation

1. Jul 22, 2008

### ismaili

1. The problem statement, all variables and given/known data
The problem is:
A proton collides with a Helium nucleus. What is the minimum lab kinetic energy needed to produce an anti-proton?

2. Relevant equations

3. The attempt at a solution
I suppose that helium nucleus is at rest in the lab frame.
I'm wondering about the final particles of this reaction.
Originally, I guess the result is a proton, an anti-proton and the helium nucleus, but in this way, the charge is not conserved. So I guess the final particles are two protons , an anti-proton and helium nucleus, but my friend told me that the standard answer in the text is that the final state is with one proton, one anti-proton and one helium nucleus.
So, the charge can be not conserved in a reaction?
(This means that the interaction is not electromagnetic?)

Thanks for all ideas.

2. Jul 22, 2008

### Dick

Charge is certainly conserved and your friend is wrong. Your guess is correct. Notice you also need to conserve baryon number. Producing a proton, anti-proton pair is really your only choice.

3. Jul 23, 2008

### confuted

Yeah, the energy for particle-antiparticle production is always $$2mc^2$$, where m is the mass of one of the particles.