Jan 10 – 15, 2021
Weizmann Institute of Science
Asia/Jerusalem timezone
See you at IS2023 in Copenhagen in June 2023

Nuclear suppression in inelastic nucleon-nucleon cross section

Jan 11, 2021, 5:45 PM
Andrea's room 2 (vDLCC)

Andrea's room 2


oral The initial stages of heavy-ion collisions IS


Dr Ilkka Helenius (University of Jyväskylä)


In high-energy heavy-ion collisions the standard procedure to turn the measured hard-process yields into centrality dependent cross sections is to use normalization factors calculated with the Monte-Carlo Glauber model. Canonically it is assumed that a necessary input, the inelastic nucleon-nucleon cross section, is unmodified wrt. the measured cross section in proton-proton collisions. At the LHC energies particle production is, however, dominated by the small-x region where nuclear suppression due to shadowing or saturation phenomena is expected. In this talk we elaborate this idea by using the recent Run 2 ATLAS data for electro-weak boson production in lead-lead collisions. Using the state-of-the art NNLO calculations we turn the canonical approach around and use the minimum-bias Z and W boson production measurements to obtain the normalization factors preferred by the data. Through Monte-Carlo Glauber simulations we find that the data prefer a significantly suppressed value for the inelastic nucleon-nucleon cross section, $41.5^{+16.2}_{-12.0}$ mb instead of the nominal $70 \pm 5$ mb. Furthermore, using the obtained value, the unexpected rise of Z and W boson nuclear modification ratios towards more peripheral collisions is tamed and the data become compatible with a flat behaviour or even hint of a mild decrease. Also, we demonstrate that the obtained suppression is in line with an eikonal minijet model including nuclear shadowing.

Primary authors

Dr Ilkka Helenius (University of Jyväskylä) Kari J. Eskola (University of Jyvaskyla) Hannu Paukkunen (University of Jyväskylä) Mikko Kuha

Presentation materials