Abstract
Experimental results of inclusive hard-process cross sections in heavy-ion collisions conventionally lean on a normalization computed from Glauber models where the inelastic nucleon-nucleon cross section σ_{nn}^{inel}-a crucial input parameter-is simply taken from proton-proton measurements. In this Letter, using the computed electroweak boson production cross sections in lead-lead collisions as a benchmark, we determine σ_{nn}^{inel} from the recent ATLAS data. We find a significantly suppressed σ_{nn}^{inel} relative to what is usually assumed, show the consequences for the centrality dependence of the cross sections, and address the phenomenon in an eikonal minijet model with nuclear shadowing.
Highlights
As proposed in Ref. [28], the Glauber model and its inputs could be tested by studying the production of well known “standard candles,” such as EW bosons, in Pb þ Pb collisions at the LHC, but so far this has been limited by the precision of the LHC Run-I measurements [24,25,26,38]
=dy dσ WppÆ ;Z =dy where the per-event yield is normalized into nucleonnucleon cross section by diving with the mean nuclear overlap hTPbPbi 1⁄4 hNbinic=σinnnel obtained from a Monte Carlo (MC) Glauber model calculation
8.469 5.808 3.300 1.733 0.595 0.096 7.624 6.118 discussed, e.g., in the ATLAS publications [39,40], such a suppression could be expected from selection and geometrical biases associated with the MC Glauber modeling
Summary
Letter, using the computed electroweak boson production cross sections in lead-lead collisions as a benchmark, we determine σinnnel from the recent ATLAS data. At high enough energies, like those at the LHC, the particle production becomes sensitive to QCD dynamics at small momentum fractions x where some suppression is expected due to gluon shadowing [32,33,34] or saturation phenomena [35,36,37] Such effects become more pronounced in heavy nuclei and toward lower scales, so one could argue that, in collisions involving heavy ions, the value of σinnnel should be reduced relative to what is measured in proton-proton collisions. Eq (1), this would change the obtained hard cross sections and nuclear modification ratios and thereby affect
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
