Griffiths Introduction to Elementary Particles · Problem 10.4

Weak Interactions — David J. Griffiths

Physics — QFT · neutron-decay-amplitude

Problem

Show that the amplitude for neutron beta decay gives ⟨∣M∣2⟩=2(gwMWc)4(p1⋅p2)(p3⋅p4)\langle |\mathcal{M}|^2 \rangle = 2\left(\frac{g_w}{M_W c}\right)^4 (p_1 \cdot p_2)(p_3 \cdot p_4) [equation (10.43)], which is the same as (10.16), even though particle 3 is now a massive proton instead of a massless neutrino.

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