Pentaquark Particles: New Doubts Cast on Their Existence in Recent Experiment

[humanino]

You said "pentaquark" !?

All right, it is now officially released :
Doubt is cast on pentaquarks
Another dedicated experiment in the same lab is still under the process of data analysis. Let us hope they will agree with each other !

 

[Norman]

This is good. I always really felt that the pentaquark didn't fit in. I never really liked the idea, it felt quite odd to me to have a pentaquark particle. But I suppose the jury is still out, so I will have to wait and see.

 

[Adrian Baker]

Is there any particle made up of more than 3 quarks? I read the Pentaquark link, but didn't I hear news of a suspected 4 quark particle some time back?

Thanks

 

[El Hombre Invisible]

I doubt it. Unless it were two quark-antiquark pairs, which annihilate straight away, color would not be confined.

 

[juvenal]

I doubt it. Unless it were two quark-antiquark pairs, which annihilate straight away, color would not be confined.

4-quark and 5-quark systems can be colorless because 2 and 3 quark system are colorless and sums of colorless systems are also colorless.

And quark-antiquark pairs do not necessarily annihilate "straight away". See charmonium.

 

[El Hombre Invisible]

Tell me about charmonium.

 

[Meir Achuz]

I think there might be a confusion about language.
"Pentaquark" does not mean 5 quarks.
The PQ is composed of 3 quarks and an additional quark-antiquark pair.
This makes it a bit like a molecule of a baryon and a meson, and not all that exotic.
Its narrow width, if obvserved, is what makes it unusual.
"Four quark" states really mean two quarks and two antiquarks.
They were hot about 20 years ago, and were called "baryonium".
They fell into disrepute, but strong evidence for them was never overturned.
The quarks would not immediately annihilate if they formed two diquarks some distance apart.

 

[El Hombre Invisible]

Well, that's like calling a helium nucleus a dodecaquark!

 

[juvenal]

Tell me about charmonium.

http://www.slac.stanford.edu/history/revolution.shtml