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Since we will (maybe) never observe free quarks which has fraction charge, is it logically correct to say that the fraction (1/2,2/3 etc) electric charge is also confined. I.e. the charges that we do se (+1,-1 etc) are "white" in the sense of color?

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As currently formulated the question is nonsensical. Electric charge is a different quantum number than color and it does not make sense to ask if electric charge is color neutral: they are orthogonal. –  dmckee Dec 20 '13 at 21:03

2 Answers 2

I don't see the analogy.

Isolated color charged particles (quarks) have not been observed, this is not the case electric charge particles (like electrons) because we observe total net electric charge.

You might mean that fractional color has not been observed, neither fractional electric charge. In that case, it's true, but this is not what confinement means.

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Perhaps I should be clearer. I mean that as long as quarks are confined, so is their 1/3 or 2/3 fraction electric charge. –  Love Learning Dec 20 '13 at 14:57
    
I think that you could say something like that, because you always observe integer charge. But the reason of quark confinement is strong interaction (color). –  jinawee Dec 20 '13 at 15:00
    
I edited the question a little. –  Love Learning Dec 20 '13 at 15:01
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Fractional charge has been observed! Because the top quark lifetime is shorter than confinement time you can measure it's charge: see arxiv.org/abs/1307.4568 –  jk88 Dec 20 '13 at 15:10
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@jk88 They'd been observed before, though the analysis is admittedly more involved. –  dmckee Dec 20 '13 at 23:12

No- because electric charge can be measured (in principle) up to an infinite distance from the source, i.e. it's range (and influence) is infinite.

Colour charge can only be measured up to a range close of approximately $r_p$, the radius of the proton, i.e. its range (and influence) is confined to below a fixed distance.

As for whether the quark's electric charge is confined - no. The proton is electrically charged- but this is 'actually' the charge of the quarks in the proton. The influence of this electric charge (mixed with quantum mechanics) is why electrons can interact with protons to form atoms.

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(I edited the question a little) Yeah, I know that the proton has charge but have you measured a fraction charge? What I'm saying is that perhaps measuring a fraction charge is equivalent to measuring a single color: i.e. if you can measure one you could probably measure the other too. –  Love Learning Dec 20 '13 at 15:04
    
Ah but fractional electric charge has been measured (see my comment on jinawee's answer). The reason why a quark's colour charge can't be measured is fundamentally due to the nature of the strong force. –  jk88 Dec 20 '13 at 15:12

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