# Mesons and baryons written in terms of quarks

• I
Hello, guys.

I have not understood what it means when one writes ##\pi^+=u\bar{d}##, for example. I though it simply meant that the ##\pi^+## meson was composed of one up-quark and one anti-down-quark. However, that doesn't explain what writing ##\pi^0=\frac{1}{\sqrt{2}}(d\bar{d}-u\bar{u})## means. I'd say that writing ##\pi^+=u\bar{d}## means that the ##\pi^+## meson's wavefunction is the tensor product of the wavefunctions of ##u## and ##\bar{d}##. Is that it?

A related question: how can one draw the feynman diagram for something like ##\pi^0\rightarrow A+B##? My problem is that I usually start by writing the quarks which constitute each particle, but in this case the left hand side particle is a composition of two "states". Shall I draw one feynman diagram for ## d\bar{d}## and another one for ##u\bar{u}##?

mfb
Mentor
The ##\pi^0## is something like a superposition of ##d \bar d## and ##u \bar u##. Those are just the valence quarks, however - hadrons are complex objects, and interpreting them as just their valence quark content doesn't give an accurate description.

For Feynman diagrams involving neutral pions, choose either ##d \bar d## or ##u \bar u##.

Xico Sim
vanhees71
$$\vec{\pi}=\bar{\psi} \vec{\tau} \psi,$$
$$\pi_{\pm} = \pi_1 \pm \mathrm{i} \pi_2, \quad \pi_0=\pi_3.$$