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Peeling away neutron skin in ultracentral collisions of relativistic nuclei

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Abstract

In heavy nuclei the ratio between local densities of neutrons and protons increases towards the nuclear periphery. The excess of neutrons is known as the neutron skin (NS) with a subtle difference (\(<0.5\) fm) between the r.m.s radii of the distributions of neutrons and protons. We show that the presence of NS in \(^{208}\)Pb leads to extra spectator neutrons in ultracentral \(^{208}\)Pb–\(^{208}\)Pb collisions at the CERN SPS and LHC. The yields of spectator neutrons and protons were calculated within a new version of Abrasion–Ablation Monte Carlo for Colliders model (AAMCC-MST) taking into account NS and pre-equilibrium clustering of spectator matter. While the average numbers of spectator neutrons and protons in ultracentral collisions vary insignificantly, the cross sections of emission of certain numbers of spectator neutrons in events with 0,1,...5 spectator protons are changed by 50–250%, depending on the thickness of NS. These cross sections are less sensitive to other parameters in calculations, and their measurements in the ALICE experiment at the LHC will make it possible to restrict the variety of neutron density parameterizations existing for \(^{208}\)Pb.

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Data Availability Statement

This manuscript has no associated data or the data will not be deposited. [Authors’ comment: Data sharing is not applicable to this article as no new experimental data were created or analyzed in this study.]

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Acknowledgements

One of the authors (I.P.) is grateful to Dariusz Miskowiec and Chiara Oppedisano for the discussions which stimulated the investigation of the effects of neutron skin in ultrarelaticistic \(^{208}\)Pb–\(^{208}\)Pb collisions.

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Authors and Affiliations

  1. Moscow Institute of Physics and Technology, Institutskiy per. 9, Dolgoprudny, Moscow Region, 141701, Russia

    Nikita Kozyrev, Aleksandr Svetlichnyi, Roman Nepeivoda & Igor Pshenichnov

  2. Institute for Nuclear Research of the Russian Academy of Sciences, Prospekt 60-letiya Oktyabrya 7a, Moscow, 117312, Russia

    Nikita Kozyrev, Aleksandr Svetlichnyi, Roman Nepeivoda & Igor Pshenichnov

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  1. Nikita Kozyrev
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Kozyrev, N., Svetlichnyi, A., Nepeivoda, R. et al. Peeling away neutron skin in ultracentral collisions of relativistic nuclei. Eur. Phys. J. A 58, 184 (2022). https://doi.org/10.1140/epja/s10050-022-00832-5

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