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This question relates to Griffiths: Introduction to Elementary Particles, p. 196
The process in question is a neutral pion decay into two photons. It is stated that because the secondary particles are massless, the amplitude for this process is:
<br /> M(p_2,p_3)<br />
where p_2 and p_3 are the momentum three-vectors of the secondary photons. Conservation of momentum further implies that p_2=-p_3. So far, so good.
However, Griffiths then states that
<br /> |M|^2<br />
is a function of |p_2| only, meaning that |M|^2 has no angular dependency. Why is this?
The process in question is a neutral pion decay into two photons. It is stated that because the secondary particles are massless, the amplitude for this process is:
<br /> M(p_2,p_3)<br />
where p_2 and p_3 are the momentum three-vectors of the secondary photons. Conservation of momentum further implies that p_2=-p_3. So far, so good.
However, Griffiths then states that
<br /> |M|^2<br />
is a function of |p_2| only, meaning that |M|^2 has no angular dependency. Why is this?
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