The Effects Of Initial Structure On Heavy Ion Collision At Medium Energy

The equation of state(EOS)of nuclear matter,which deals with the thermodynamic relationship between nuclear energy,nuclear matter density,isospin asymmetry and temperature,has always been a research hotspot in nuclear physics.Heavy ion collision experiment combined with transport model simulation is a common method to extract the properties of nuclear matter.Nuclear structure information(such as the shape,the density distribution of neutron and protons,the distribution of nucleon momentum,etc.)is one of the input quantities of transport model.Therefore,it is very important to explore the influence of nuclear structure information on observables in heavy ion collisions.As we all know,many of heavy nuclei have ellipsoid deformation in the ground state.Therefore,it is of great significance to explore the influence of deformation on the observables the final state.Based on the ultra-relativistic quantum molecular dynamics(Ultrarelativistic Quantum Molecular Dynamics)model,the structure effect of projectile and target is considered in the initial sampling part and then ellipsoid deformation is introduced.In order to study the influence of initialization structure effect on observables in heavy ion collisions,two kinds of ellipsoid collisions with extreme structures:Tip-Tip collision(the two nuclei with their long axes head-on)and Belly-Belly collision(the two nuclei with their short axes head-on and long axes parallel in the reaction plane)are selected,and the results of sphere-sphere(SP-SP)collision are compared.The effect of nuclear deformation in ²³⁸U+²³⁸U at the beam energy of 0.15,0.2,0.4,0.8,and 1.5 Ge V/nucleon is investigated.And several observables,such as the stopping power and the collective flow,as well as ?^-/?⁺yield ratio are calculated.It is found that the stopping power obtained with Tip-Tip collisions is the largest among collisions with different deformations.This is due to the longer duration of high temperature and high density fireballs in tip to tip collision reaction.For Belly-Belly collisions,the elliptic flow exits even for the most central collision(b=0 fm);?^-/?⁺ yield ratio obtained with tip-tip collision is larger than that obtained with belly-belly collision.;When the ?^-/?⁺ yield ratio is used to detect the density dependent behavior of symmetry energy,the effect of deformation should be paid attention.In addition,the influence of nuclear deformation on the elliptic flow of free protons is stronger than symmetry energy in ²³⁸U+²³⁸U collisions at 0.4 Ge V/nucleon,while the elliptic flow ratio between neutrons and protons shows hardly any sensitivity to the different deformation of Uranium.