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arXiv · 2509.21644

Neutron Skin from Conserved Charge Measurements at Collider Experiments

Grégoire Pihan·Akihiko Monnai·Björn Schenke·Chun Shen
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Abstract

We propose a novel method for measuring the neutron skin of heavy nuclei using collider experiments. Specifically, we demonstrate that the neutron skin thickness of the lead nucleus can be extracted in $p$+$^{208}$Pb collisions by analyzing a double ratio: The ratio of net electric charge to net baryon number measured near the lead-going rapidity, taken for high-multiplicity events and divided by the same ratio for low-multiplicity events. We compute the expected sensitivity of the double ratio to the neutron skin within a comprehensive (3+1)D relativistic hydrodynamic framework that incorporates multiple conserved charge currents and a charge-dependent lattice-QCD-based equation of state. We provide predictions for both $p$+$^{208}$Pb collisions at ${\sqrt{s_{\mathrm{NN}}}=72}$~GeV and $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV, corresponding to the center of mass energies realized in the SMOG2 fixed-target setup at LHCb and the LHC collider mode, respectively.

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Grégoire Pihan, Akihiko Monnai, Björn Schenke, Chun Shen. 2025-09-25. Neutron Skin from Conserved Charge Measurements at Collider Experiments. https://arxiv.org/abs/2509.21644

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