I am answering a question about a particle decaying into two other particles and one needs to find the momentum of the children particles from the rest frame of the parent. I found a very helpful article on Wikipedia under 'Particle Decay', however I am really confused by their mathematical working and wondering if anyone can explain it or agree with me that Wiki has made a mistake :)(adsbygoogle = window.adsbygoogle || []).push({});

I can't copy all the equations so the link is here: http://en.wikipedia.org/wiki/Particle_decay

its under the Sub heading Conservation of four momentum.

I don't understand how they can expand 2(p_M*p_1) into only 2 terms when under normal (a+b)(c+d) expansions you get four. Unless there is some wierd vector multiplication I don't understand?

Any help GREATLY appreciated!

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# Particle decay and relativity

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