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Q & A: Annihilation and High Energy Collisions

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Most recent answer: 05/08/2010
Q:
when matter and antimatter annihillate, does it only happen if the opposites collide (i.e. if hydrogen collides with antihydrogen) or if any matter and antimatter collide?
- charles (age 17)
bremerton, WA
A:
Annihilation will only occur between a particle and its respective anti-particle. So, yes, the electron and proton in the hydrogen will annihilate with the positron and antiproton in the antihydrogen.

That is, by definition, what annihilation means. Two particles (a particle and antiparticle) collide and produce two photons (or two W/Z-bosons, or two gluons -- depending on what type of interaction governs it), because energy must be conserved. It is also possible for more than one pair of photons to be produced, but the probability of that happening decreases significantly with each extra pair produced.

However, two different particles can collide at high energies and create other particles as well. It's an interesting process, and a lot of weird stuff happens! For example, two high energy protons can collide an create a 3 protons and an antiproton! (with a lower net kinetic energy than the original protons, of course.) Also, a lot of exotic particles are created this way from cosmic rays hitting our atmospheres and at particle accelerators. It is also interesting to note how rest mass is not conserved in these collisions, but total energy always is conserved. This is because energy and mass are closely related by E=mc2, so you could say that mass energy is conserved.

-- Natasha S.


(published on 05/08/2010)

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