A. Rosenhauer

The role of quantum effects and non-equilibrium transport coefficients for relativistic heavy ion collisions

Stopping power and thermalization in relativistic heavy ion collisions is investigated employing the quantum molecular dynamics approach. For heavy systems stopping of the incoming nuclei is predicted, independent of the energy. The influence of the quantum effects and their increasing importance at low energies, is demonstrated by inspection of the mean free path of the nucleons and the n-n collision number. Classical models, which neglect these effects, overestimate the stopping and the thermalization as well as the collective flow and squeeze out. The sensitivity of the transverse and longitudinal momentum transfer to the in-medium cross section and to the pressure is investigated.

Equilibration of a Three Component Nuclear System in Heavy-Ion Collisions

A system of three different nuclear matter components is introduced to describe the nucleons participating in a high-energy heavy-ion reaction. The first and second component is attributed to the nucleons of target and projectile, while a third component is taken into account to study the formation of thermalized matter in the course of the reaction. It is assumed that the distributions of the incoming nuclei are equilibrated ones and that collisions of nucleons belonging to different distribution components populate the thermalized matter component. Then, by means of Boltzmann transport theory the time evolution of such a three-component system for infinite uniform nuclear matter is calculated. The process of thermal equilibration is studied and the results are compared to the ones of other kinetic model calculations. Observable signs of the equilibration process are pointed out.

Confrontation of Theoretical Approaches and Experimental Data on High Energy Heavy Ion Collisions

We give an overview of high energy heavy ion collisions. The merits and drawbacks of macroscopic and microscopic theoretical approaches (Fluid Dynamics, TDHF, Cascade, Vlasov-Uehling-Uhlenbeck, Classical and Quantum Molecular Dynamics) are discussed. The importance of nonequilibrium transport properties (viscosity, mean free path, effective in-medium cross sections) and of the nuclear potential (equation of state) is pointed out. The liquid-vapour phase transition and multifragmentation have been studied. The possibility of meassuring Machshock fragments in inverse kinematics experiments is also pointed out. It is demonstrated that the projectile and target are stopped at YCM if central collisions are studied. The stopping is only sensitive to σeff. The predicted bounce-off of the rather cold fragments in the reaction plane and the predicted accompanying squeeze-out of the hot participant baryons perpendicular to the reaction plane are experimentally discovered. These effects are sensitive both to the viscosity (σeff(ρ,E,Ω)) and to the generalized equation of state (optical potential U(ρ, E)). The data clearly ask for a repulsive potential interaction. We conclude that nuclear matter produced in relativistic collisions is a hot, dense, viscous and rather incompresible fluid, with important quantum properties.

Future experiments with polarized beams and targets in relativistic heavy-ion collisions

Abstract The influence of shape deformations in relativistic heavy ion collisions at energies between 0.8 and 2.1 GeV/n is analysed on the basis of an intra-nuclear cascade simulation for the systems 46 Ti + 46 Ti and 166 Er + 166 Er . The assumption that the incoming nuclei are treated as spheres of nuclear gas is replaced by more realistic nuclear shapes. Considering polarized beams and targets, i.e. fixing the orientation of the deformed nuclei with respect to each other, considerable changes in global variables can be expected for central and almost central collisions.

Multicomponent transport theoretical approach to ultrarelativistic heavy ion collisions

A new theoretical model is introduced which is able to describe the initial compression and thermalization stage of an ultrarelativistic heavy-ion collision in a hydrodynamical three-flow picture. The first and second fluid is attributed to the nucleons of target and projectile, while a third component is introduced in order to take into account the gradual thermalization of the incoming flow. Based on relativistic transport theory, hydrodynamic equations of motion are derived for each component including transitions of target and projectile nucleons to the thermalized matter component as well as mutual deceleration accompanied with gradual heat transfer between the components. Hence, the multicomponent formalism contains the former two fluid approach as a limiting case.

Momentum distribution of nuclear matter in energetic heavy-ion collisions

SummaryThe reaction of two colliding heavy ions is described by the development of three momentum distribution functions. Two of those distributions represent the nucleons of target and projectile, while a third component is introduced to study the formation of thermalized nuclear matter in the course of the reaction. One may assume that collisions of nucleons belonging to target and projectile component populate the thermalized one. The momentum distribution function of the singly collided nucleons belonging previously to two different Maxwell-Boltzmann distributions can be computed. We analyse under which assumptions the distribution function of the once collided nucléons can be approximated by a thermal-equilibrium distribution.RiassuntoSi descrive la reazione di due ioni pesanti in collisione mediante lo sviluppo di tre funzioni di distribuzione dell’impulso. Due di queste distribuzioni rappresentano i nucleoni del bersaglio e del proiettile, mentre s’introduce una terza componente per studiare la formazione di materia nucleare termalizzata durante la reazione. Si può presumere che le collisioni dei nucleoni che appartengono alle componenti bersaglio e proiettile popolino la componente termalizzata. Si può calcolare la funzione di distribuzione dell’impulso dei nucleoni a collisione singola che appartenevano precedentemente a due diverse distribuzioni di Maxwell-Boltzmann. Si analizza sotto quali ipotesi la funzione di distribuzione dei nucleoni a collisione singola si può approssimare con una distribuzione di equilibrio termico.РезюмеИспользуя трех-импульсные функции распределения, описывается взаимодействие двух соударяющихся тяжелых ионов. Два из этих распределений представляют нуклоны мишени и налетающей частицы, тогда как третья компонента вводится для изучения образования термализованного ядерного вещества в процессе реакции. Можно предположить, что соударения нуклонов, принадлежащих мишени и налетающей частицы, приводит к заселению термализованной компоненты. Можно вычислить функцию распределения по импульсам для соударяющихся нуклонов, ранее принадлежащих двум различным распределениям Максвелла-Больцмана. Мы анализируем, при каких предположениях функция распределения для однократно соударившихся нуклонов может быть аппроксимирована распределением теплового равновесия.