- #1

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## Homework Statement

For the following reactions draw Feynman diagrams, clearly labelling all the quarks, leptons and exchanged particles and stating the type of interaction involved (if more than one interaction could be involved give the most likely):

(i) ##\pi^0 \to \gamma + \gamma##

(ii) ##\bar{\Lambda} \to \bar{n}+\pi^0##

(iii) ##e^+ + e^- \to \nu_\tau + \bar{\nu_\tau}##

## The Attempt at a Solution

For

**(i)**the pion decays into two photons. But the quark composition of ##\pi^0## is given by both ##u\bar{u}## and ##d\bar{d}##, so which one should I use in the diagram?

Also I believe it decays by the weak interaction, but where exactly should I place the W

^{-}line on the diagram? Here's the diagram so far:

**(ii)**Is ##\bar{\Lambda}## referring to the antiparticle of neutral lambda (##\Lambda^0##)? Here is my attempt:

Is this correct?

**(iii)**Is this the weak force since there are neutrinos involved? I'm not 100% sure if this is the electromagnetic or weak force. Here is my diagram:

(once again time flows horizontally)

Any help with these diagrams is greatly appreciated.