Neutron-skin effect in direct-photon and charged hadron-production in   Pb+Pb collisions at the LHC
  A well-established observation in nuclear physics is that in neutron-rich spherical nuclei the distribution of neutrons extends farther than the distribution of protons. In this work, we scrutinize the influence of this so called neutron-skin effect on the centrality dependence of high-$p_{\rm T}$ direct-photon and charged-hadron production. We find that due to the estimated spatial dependence of the nuclear parton distribution functions, it will be demanding to unambiguously expose the neutron-skin effect with direct photons. However, when taking a ratio between the cross sections for negatively and positively charged high-$p_{\rm T}$ hadrons, even centrality-dependent nuclear-PDF effects cancel, making this observable a better handle on the neutron skin. Up to 20~\% effects can be expected for the most peripheral collisions. 
Ilkka Helenius, Hannu Paukkunen, Kari J. Eskola
hep-ph nucl-th