We present new quantitative predictions for the distribution of the total invariant mass produced diffractively in dipole-nucleus scattering at large relative rapidity. We show that the shape of this distribution is intimately related to the properties of the fluctuations in the small-x partonic evolution. This observable can potentially be measured at a future electron-ion collider.
Based on Phys.Rev.Lett. 121 (2018) no.8, 082001; Phys.Rev. D98 (2018) no.3, 034021 and work in progress.