High density QCD and nucleus–nucleus scattering deeply in the saturation region

In this paper we solve the equations that describe nucleus–nucleus scattering, in high density QCD, in the framework of the BFKL Pomeron Calculus. We found that (i) the contribution of short distances to the opacity for nucleus–nucleus scattering dies at high energies, (ii) the opacity tends to unity at high energy, and (iii) the main contribution that survives comes from soft (long distance) processes for large values of the impact parameter. The corrections to the opacity Ω(Y,b)=1 were calculated and it turns out that they have a completely different form, namely () than the opacity that stems from the Balitsky–Kovchegov equation, which is (). We reproduce the formula for the nucleus–nucleus cross section that is commonly used in the description of nucleus–nucleus scattering, and there is no reason why it should be correct in the Glauber–Gribov approach.