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# 8.5: Color Symmetry

So why don’t we see fractional charges in nature? This is an important point! In so-called deep inelastic scattering we see pips inside the nucleon – these have been identified as the quarks. We do not see any direct signature of individual quarks. Furthermore, if quarks are fermions, as they are spin $$1/2$$ particles, what about antisymmetry of their wavefunction?

Let us investigate the $$\Delta^{++}$$, see Figure $$\PageIndex{1}$$, which consists of three $$u$$ quarks with identical spin and flavor (isospin) and symmetric spatial wavefunction,

$\psi_{\rm total} = \psi_{\rm space} \times \psi_{\rm spin} \times \psi_{\rm flavour}.$

This would be symmetric under interchange, which is unacceptable. Actually there is a simple solution. We “just” assume that there is an additional quantity called colour, and take the colour wave function to be antisymmetric:

$\psi_{\rm total} = \psi_{\rm space} \times \psi_{\rm spin} \times \psi_{\rm flavour} \times \psi_{\rm colour}$

We assume that quarks come in three colours. This naturally leads to yet another $$SU(3)$$ symmetry, which is actually related to the gauge symmetry of strong interactions, QCD. So we have shifted the question to: why can’t we see colored particles?

This is a deep and very interesting problem. The only particles that have been seen are colour neutral (“white”) ones. This leads to the assumption of confinement – We cannot liberate colored particles at “low” energies and temperatures! The question whether they are free at higher energies is an interesting question, and is currently under experimental consideration.