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Maybe a stupid question because my search didn't return anything.

Assuming in low energy state, a proton (made by a red up, a blue up and green down quarks) meets an anti-neutron (made by an anti-green up, an anti-red down and an anti-blue down quarks). Will they stay together without annihilation because of unmatched color charges? Or gluons will be emitted to change colors so annihilation happens?

Mostafa
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user29518
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1 Answers1

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Although it's commonly said that a nucleon contains three quarks, it's more accurate to say that the net number of quarks (i.e. number quarks - number anti-quarks) is equal to three. The interior of a nucleon is a fantastically dynamic place and the number of quarks and gluons at any instant is typically much greater than three.

So it is wrong to imagine the proton as containing a red up, a blue up and green down quarks. All you can say is that the net red charge, net green charge and net blue charge will all be one.

You comment gluons will be emitted to change colors so annihilation happens is sort of true, but it's a bit misleading to imagine there is, for example, a distinct down quark that is green and you need to wait for a gluon to be emitted before it changes colour. A better way of describing this would be to say the down quark is in a superposition of all colour charges.

John Rennie
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  • Thank you for the answer. Let me make sure that I really understand: I can't say for sure if this proton will annihilate with anti-neutron or not because color charges of quarks are governed by probability not certainty. I can only say it has a good chance to annihilate and find out by making an observation to collapse probability into certainty. – user29518 Sep 12 '13 at 07:55
  • See http://physics.stackexchange.com/questions/18795 and the links therein. The proton anti-neutron annihilation is slow by the stands of nuclear reactions, but always happens eventually. – John Rennie Sep 12 '13 at 08:29
  • A question somewhat related to this intriguing answer .. http://physics.stackexchange.com/questions/217371/changing-or-static-quark-color-composition-within-a-proton – Fattie Nov 09 '15 at 23:39
  • Or in other words, those two baryons do not have unmatched color charges, they are both white. – Shufflepants Mar 20 '18 at 20:58