Instantons and Saturation in the Colour Dipole Picture
We pursue the intriguing possibility that larger-size instantons build up diffractive scattering, with the marked instanton-size scale hi ≈ 0.5 fm being reflected in the conspicuous "geometrization" of soft QCD. As an ex- plicit illustration, the known instanton contribution to DIS is transformed into the intuitive colour dipole picture. With the help of lattice results, the q¯-dipole size r is carefully increased towards hadronic dimensions. Unlike pQCD, one now observes a competition between two crucial length scales: the dipole size r and the sizeof the background instanton that is sharply localized around hi ≈ 0.5 fm. For r > ∼ hi , the dipole cross section in- deed saturates towards a geometrical limit, proportional to the areahi 2 , subtended by the instanton.