Why do you get photons or other particles in annihilation of subatomic particles?

Answer 1

In annihilation between electron and positron, you should get nothing in your hand. Instead of that you get a pair of photons. The question is that why should you get the pair of photons. So this is not complete annihilation. The answer is simple to this question. When you bring the electron and positron slowly to each other, they will annihilate to each other and will not produce the photons also. But when the particles come with high speed, they carry the energy and have momentum. This energy is converted into photons of different wave length and the electron and positron disappear or get completely annihilated. When you have heavy particles like protons and anti-protons or neutrons and anti-neutrons strike to each other, you get much larger amount of energy that is left. Because they are brought to each other at high speed, they have high momentum and so carry the large amount of energy. This energy is liberated after the annihilation. When enough quantum of energy is there, you have production of electrons, positrons and neutrinos get generated. The rest of the energy is left in the form of photons. When larger molecules of matter and antimatter will collide with each other, you may get smaller molecules of matter and antimatter in your hand.