Clustered Nature of Hot and Dense Nuclear Matter: Signatures from Heavy-Ion Collisions

Although light nuclear clusters are known to form abundantly in warm and dilute nuclear matter, their role in hot and dense nuclear matter remains unclear due to the lack of experimental indication for their modifications by the Mott effect under such conditions. To address this issue, we resort to intermediate-energy heavy-ion collisions, where light clusters are mainly produced in the transiently formed hot and dense matter. A kinetic approach, which includes dynamically the formation and dissociation of light clusters, is employed to deduce the strength of the Mott effect and the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>α</a:mi> </a:mrow> </a:math> -particle fraction in hot and dense nuclear matter from the light-nuclei yields measured by the FOPI Collaboration in central <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mrow> <c:mi>Au</c:mi> <c:mo stretchy="false">+</c:mo> </c:mrow> <c:mi>Au</c:mi> </c:mrow> </c:math> collisions at energies of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mrow> <f:mn>0.25</f:mn> <f:mi>A</f:mi> </f:mrow> </f:math> to <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mrow> <h:mn>0.6</h:mn> <h:mi>A</h:mi> <h:mtext> </h:mtext> <h:mi>GeV</h:mi> </h:mrow> </h:math> . We find an unexpectedly abundant <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>α</j:mi> </j:math> clustering in this environment, which will have profound implications for modeling the nuclear equation of state and describing supernovae and neutron star mergers.