# Pi Meson

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1. Sep 25, 2015

### Garlic

Hello,
I understand the fact that pi mesons are superpositions of uubar and ddbar. But what happens if a decay only produces a single type of meson? I am not sure of this, but omega baryon decaying into xi-minus and a neutral pion seems to produce ddbar mesons, is it so that only a single type of meson gets formed and then it oscillates between uubar and ddbar because of the relatively same mass those two mesons have?
Imagine that I'm bombarding protons with neutral pi mesons, how would the feynman diagramm look like? When we make pions react with other matter is it so that we are "measuring" it, and therefore forcing it to be in a certain eigenstate?
As far as I've understood, the composition of neutral pions are uubar - ddbar / sqrt2 is so because of the sightly higher mass of down quarks. Why isn't there be two neutral pions that have different mass and different composition, so that, the one we know, the normal neutral pion is going to have smaller mass, and the other neutral pion is going to be heavier with this composition uubar + ddbar / sqrt2 ?
Thank you

2. Sep 25, 2015

### Staff: Mentor

The pi0 is a single particle, it is not oscillating. It even has a small strange/antistrange contribution. The QCD production of the particle "makes sure" it is produced in the right state. For the production and decay process, it can be regarded as u/ubar or d/dbar combination, but it actually is always a superposition of those.

3. Sep 25, 2015

### Orodruin

Staff Emeritus
Just to mention, the flavour combinations which are orthogonal to the pi0 are the eta mesons. These have masses which are different from the pi0.

4. Sep 25, 2015

### Garlic

Could you please recommend me a source to read? I need to understand the structure of pi mesons better. (It needs to be a free pdf- I'm not near a library and I don't have a credit card)

Thank you