Evidence of shadowing in inelastic nucleon-nucleon cross section

The Glauber modeling plays a key role in centrality-dependent measurements of heavy-ion collisions. A central input parameter in Glauber models is the inelastic nucleon-nucleon cross section sigma(inel)(nn) which is nearly always taken from proton-proton measurements. At the LHC energies sigma(inel)(nn) depends on the QCD dynamics at small x and low interaction scales where the shadowing/saturation phenomena are expected to become relatively more important for larger nuclei than for the proton. Thus, sigma(inel)(nn) e.g. in Pb+Pb collisions may well be lower than what is seen in proton-proton collisions. In this talk, we demonstrate how to use the recent W-+/- and Z measurements as a "standard candle" to extract sigma(inel)(nn) in Pb+Pb collisions. Our analysis - built on the ATLAS data, state-of-the-art NNLO QCD calculations and nuclear PDFs - indicate that at the LHC energies sigma(inel)(nn) nn in Pb+Pb collisions is suppressed relative to the proton-proton measurements by tens of percents. We demonstrate that this is in line with expectations from nuclear PDFs.