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

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Two body decay and momentum

**Physics Forums | Science Articles, Homework Help, Discussion**