Disentangling the neutron skin of 48Ca from nuclear radius effects through 48Ca+48Ca and 48Ti+48Ti flow observables
Abstract
The thickness of the neutron skin (Δrnp) in 48Ca remains uncertain. CREX and ab initio calculations point to a thin skin, while many energy density functionals prefer larger values. Relativistic heavy-ion collisions can probe the skin through its geometric imprint on the quark-gluon plasma, but a thicker skin also changes the overall nuclear size, so the two effects are hard to separate. We resolve this by systematically comparing 48Ca+48Ca and 48Ti+48Ti collisions at √(sNN)=5.02 TeV using the AMPT model with string melting. For 48Ca, we take a zero-skin baseline and skins at the CREX lower and upper bounds. As size references, we add 48Ti and a skin-free 48Ca with the same density parameters as 48Ti, which separates size from skin effects. The sensitivity to the 48Ti radius is tested using two choices for its Woods-Saxon radius, one of which reproduces the experimental rms radius. We find that the neutron skin is a purely geometric perturbation; the medium's transport response coefficients are unchanged, first-moment observables exhibit only modest sensitivity to Δrnp, while second-moment observables respond much more strongly. The final-state covariance between flow and mean transverse momentum fluctuations, with its normalized correlation, is the most promising measurable probe. The radius-matched 48Ca follows 48Ti closely, and the position of 48Ti relative to the skin configurations depends on its radius. These collisions, analyzed with second-moment and shape-size correlators, offer a promising independent constraint on the 48Ca neutron skin at the LHC.
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BibTeX
@misc{saha2026disentangling,
title = {{Disentangling the neutron skin of $^48$Ca from nuclear radius effects through $^48$Ca+$^48$Ca and $^48$Ti+$^48$Ti flow observables}},
author = {Abhisek Saha},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38424},
eprint = {2610.38424},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38424},
}
RIS
TY - UNPB
TI - Disentangling the neutron skin of ^48Ca from nuclear radius effects through ^48Ca+^48Ca and ^48Ti+^48Ti flow observables
AU - Abhisek Saha
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38424
UR - https://arxiv.org/abs/2610.38424
AB - The thickness of the neutron skin (Δr_np) in ^48Ca remains uncertain. CREX and ab initio calculations point to a thin skin, while many energy density functionals prefer larger values. Relativistic heavy-ion collisions can probe the skin through its geometric imprint on the quark-gluon plasma, but a thicker skin also changes the overall nuclear size, so the two effects are hard to separate. We resolve this by systematically comparing ^48Ca+^48Ca and ^48Ti+^48Ti collisions at √(s_NN)=5.02 TeV using the AMPT model with string melting. For ^48Ca, we take a zero-skin baseline and skins at the CREX lower and upper bounds. As size references, we add ^48Ti and a skin-free ^48Ca with the same density parameters as ^48Ti, which separates size from skin effects. The sensitivity to the ^48Ti radius is tested using two choices for its Woods-Saxon radius, one of which reproduces the experimental rms radius. We find that the neutron skin is a purely geometric perturbation; the medium's transport response coefficients are unchanged, first-moment observables exhibit only modest sensitivity to Δr_np, while second-moment observables respond much more strongly. The final-state covariance between flow and mean transverse momentum fluctuations, with its normalized correlation, is the most promising measurable probe. The radius-matched ^48Ca follows ^48Ti closely, and the position of ^48Ti relative to the skin configurations depends on its radius. These collisions, analyzed with second-moment and shape-size correlators, offer a promising independent constraint on the ^48Ca neutron skin at the LHC.
ER -