The technical reasons are known as "Lepton number conservation" or "Baryon number conservation" coupled with "charge conservation". When you add the appropriate baryon and lepton numbers and know the beginning charge of both particles, all three of these numbers must be equal before and after the reaction. Lepton and Baryon numbers are typically negative for anti-matter and positive for normal matter, so when you have the reaction, in the end the numbers must be negative just like they started. So you will end up with as much anti-matter as you started with.
Answered by: Eugene Geis, M.S., Physics Grad Student, ASU, Phoenix, AZ
Firstly, I should make it clear that when two matter particles collide at high energy, only new matter-antimatter particle PAIRS can be created from the interaction. This fact becomes obvious when one considers that charge, lepton and baryon number are all conserved quantities. New anti-matter particles cannot be create by themselves, as conservation laws would be violated. Once this is understood the creation of new particles can simply be understood as the conversion of energy to matter-antimatter pairs. Importantly, you should realize that the antimatter products will eventually annihilate with matter (although perhaps after further decays) unless the antimatter is forcefully isolated.
In the example given, relativity tells us that the electron is at high enough energy in order for the proton to appear (relative to its motion) as a flat disc, with the quark motion almost stopped. The electron then interacts electromagnetically with the quarks at close distance and considerably disturbs them. Since quarks cannot exist in isolation, a lone quark cannot be removed from the proton and instead the energy from the strong-force field (due to the disturbance of the quarks) is used to create new matter-antimatter particle pairs. Many complex particle showers are produced in such interactions.
Clearly the above explanation of such interactions is independent of whether the colliding particles are both matter or both antimatter, and a similar interaction would occur between a positron and an anti-proton. Again, matter-antimatter particle pairs would be produced and again the antimatter must be forcefully isolated if annihilation is to be prevented.
The answer to your question is, thus, clearly yes: matter would be created when antimatter particles collide at high energy. You should understand that the matter would be produced in particle-antiparticle pairs though and isolation is difficult. Equally, you should see that this process would be of no use for creating matter for *use*, since matter is abundant in the Universe around us and we have no need to create it. However, the process is of considerable use in studying unstable fundamental matter (and antimatter) particles (e.g. charm, strange, top, bottom quarks, muon and tau, W, Z etc...). A high energy method must also be used to create then isolate antimatter when it is needed for study.
Answered by: Sam Cohen, Physics Student, LGS, UK
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