# Homework Help: Onium, how can it exist?

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1. Oct 10, 2015

### Mathilda

1. The problem statement, all variables and given/known data
How can an onium exist? Since it is a particle with its own antiparticle, how can it even exist? Shouldn't the particle and the anti-particle annihilate each other?

2. Relevant equations

3. The attempt at a solution

2. Oct 10, 2015

### Staff: Mentor

What does your research on the topic suggest? Have you found evidence of a stable onium?

3. Oct 10, 2015

### Mathilda

I've not been able to find any evidence for stable onium. But since it's an particle withit's own anti-particle it shouldn't be able to exist at all.
When it comes to positronium, it's an elektron and a positron that circulates around a common center of mass. Is it the common center of mass that stops them from annihilating each other?
And the pi-meson (π0) becomes a superposition. But how is it able to become a superposition instead of having the (for example) down-quark and the anti-downquark annihilation each other?

4. Oct 10, 2015

### Staff: Mentor

I think you'll find that all -oniums have very short half lives. The charged pions in particular have a mean lifetime of about 26 nanoseconds, while the neutral pion's ($\pi^0$) is really short at about 8 x 10-17 seconds.

So you might think of them as particles that are assembled and then live very briefly.

5. Oct 10, 2015

### Mathilda

I understand that have very short lifetimes. But how are they able to assemble at all? Or is -onium just an expression for the state just before a particle and it's antiparticle annihilate each other?

6. Oct 10, 2015

### Staff: Mentor

Well, where/how are -oniums found? Maybe do a bit of research on their discoveries?