Hi, I am learning about analysing particles decaying and am on this Wikipedia article: http://en.wikipedia.org/wiki/Particle_decay(adsbygoogle = window.adsbygoogle || []).push({});

Under the 'Two body decay' subsection, there is a description of the momentum of particles 1 and 2 from the rest frame of the parent particle.

I have two questions, firstly, it states that the momentum of particle 1 is equal to the momentum of particle 2, is this always the case? If they are of different mass I would have thought the momentums might be different as well.

Secondly, they state the equation for the momentum of particle 1 (or 2) in terms of the masses of all particles involved. I'm assuming they derived this from the equations mentioned in the preceding section about four momentum, but I cannot see how they have got that final result. When I try to dervie the momentum of particle 1 (or 2), using the results from the preceding section, I end up with: p_1 = sqrt[m_parent^2 + m_2^2 - m_1^2 -m_2\ 2m_parent].

Is anyone able to explain where they got that result from?

Any help greatly appreciated

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# Two body decay and momentum

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