Exploring the mass radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts/><mml:none/><mml:mn>4</mml:mn></mml:mmultiscripts></mml:math> and implications for nuclear structure
Rong Wang, C. Han, Xurong Chen
Abstract
In this study, we determine the mass radius of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mmultiscripts><a:mi>He</a:mi><a:mprescripts/><a:none/><a:mn>4</a:mn></a:mmultiscripts></a:math>, a very light nucleus, by examining the near-threshold <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>ϕ</b:mi></b:math>-meson photoproduction data of the LEPS Collaboration. To assess the gravitational form factor of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mmultiscripts><c:mi>He</c:mi><c:mprescripts/><c:none/><c:mn>4</c:mn></c:mmultiscripts></c:math>, we employ multiple models for the mass distribution, including Yukawa-type, exponential, Gaussian, and uniform functions. The mass radius of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mmultiscripts><d:mi>He</d:mi><d:mprescripts/><d:none/><d:mn>4</d:mn></d:mmultiscripts></d:math> is measured to be <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mn>1.70</e:mn><e:mo>±</e:mo><e:mn>0.14</e:mn></e:mrow></e:math> fm, which is approximately equal to the charge radius of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mmultiscripts><f:mi>He</f:mi><f:mprescripts/><f:none/><f:mn>4</f:mn></f:mmultiscripts></f:math>. Surprisingly, in contrast to the findings of the proton, no noticeable discrepancy between the charge radius and the mass radius is noted for the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mmultiscripts><g:mi>He</g:mi><g:mprescripts/><g:none/><g:mn>4</g:mn></g:mmultiscripts></g:math> nucleus. The proton and neutron distributions within <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mmultiscripts><h:mi>He</h:mi><h:mprescripts/><h:none/><h:mn>4</h:mn></h:mmultiscripts></h:math> are likely to be identical, confirming its regular tetrahedral structure in a new way. We propose exploring the difference between charge and mass radii as a new approach to examine the nuclear structure. Published by the American Physical Society 2024