AUTHOR=Atkinson M. C. , Dickhoff W. H. 

TITLE=Neutron skins: A perspective from dispersive optical models

JOURNAL=Frontiers in Physics

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2024.1487314

DOI=10.3389/fphy.2024.1487314

ISSN=2296-424X

ABSTRACT=<p>An overview of neutron skin predictions obtained using an empirical nonlocal dispersive optical model (DOM) is presented. The DOM links both scattering and bound-state experimental data through a subtracted dispersion relation which allows for fully consistent, data-informed predictions for nuclei where such data exist. Large skins were predicted for both <sup>48</sup>Ca (<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mtext>skin</mml:mtext></mml:mrow><mml:mrow><mml:mn>48</mml:mn></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mn>0.25</mml:mn><mml:mo>±</mml:mo><mml:mn>0.023</mml:mn></mml:mrow></mml:math></inline-formula> fm in 2017) and <sup>208</sup>Pb (<inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mtext>skin</mml:mtext></mml:mrow><mml:mrow><mml:mn>208</mml:mn></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mn>0.25</mml:mn><mml:mo>±</mml:mo><mml:mn>0.05</mml:mn></mml:mrow></mml:math></inline-formula> fm in 2020). Whereas the DOM prediction in <sup>208</sup>Pb is within 1<inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>σ</mml:mi></mml:mrow></mml:math></inline-formula> of the subsequent PREX-2 measurement, the DOM prediction in <sup>48</sup>Ca is over 2<inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>σ</mml:mi></mml:mrow></mml:math></inline-formula> larger than the thin neutron skin resulting from CREX. From the moment it was revealed, the thin skin in <sup>48</sup>Ca has puzzled the nuclear-physics community as no adequate theories simultaneously predict both a large skin in <sup>208</sup>Pb and a small skin in <sup>48</sup>Ca. The DOM is unique in its ability to treat both structure and reaction data on the same footing, providing a unique perspective on this <inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mtext>skin</mml:mtext></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> puzzle. It appears vital that more neutron data be measured in both the scattering and bound-state domain for <sup>48</sup>Ca to clarify the situation.</p>