Nuclear Bubble Configuration in Heavy-Ion Collisions

We study the effects of a bubble configuration in a nucleus on heavy-ion collisions at a few tens and hundreds A MeV. We first investigate the bubble structure of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>206</mn></msup></semantics></math></inline-formula>Hg using the relativistic continuum Hartree–Bogoliubov theory and then study the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>206</mn></msup></semantics></math></inline-formula>Hg + <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>208</mn></msup></semantics></math></inline-formula>Pb and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>206</mn></msup></semantics></math></inline-formula>Hg+<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>206</mn></msup></semantics></math></inline-formula>Hg reactions using the DaeJeon–Boltzmann–Uehling–Uhlenbeck (DJBUU) transport model. To see the role of the bubble structure, we consider the maximum density of the produced nuclear matter, directed flow of neutrons and protons, and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>π</mi><mo>−</mo></msup><mo>/</mo><msup><mi>π</mi><mo>+</mo></msup></mrow></semantics></math></inline-formula> ratio. We observe that the maximum density is smaller with a bubble nucleus, and the directed flow of nucleons and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>π</mi><mo>−</mo></msup><mo>/</mo><msup><mi>π</mi><mo>+</mo></msup></mrow></semantics></math></inline-formula> ratio may depend on the bubble structure.