A potential version of the UrQMD(UrQMD/M) transport model and a traditional coalescence model are combined to calculate the production of ~3He fragments in central Pb+Pb collisions at SPS energies 20-80 Ge V/nucleon. ...A potential version of the UrQMD(UrQMD/M) transport model and a traditional coalescence model are combined to calculate the production of ~3He fragments in central Pb+Pb collisions at SPS energies 20-80 Ge V/nucleon. It is found that the Lorentz transformation in the afterburner influences visibly the ~3He yield and should be considered in calculations. The rapidity distribution of ~3He multiplicities(including the concave shape) can be described well with Ur QMD/M when it stops during t_cut=(100±25) fm/c and the coalescence afterburner with one parameter set of(R_0,P_0)=(3.8 fm, 0.3 Ge V/c) is taken into use afterwards.展开更多
Rapidity distributions of both E895 proton data at AGS energies and NA49 net proton data at SPS energies can be described reasonably well with a potential version of the Ur QMD in which mean-field potentials for both ...Rapidity distributions of both E895 proton data at AGS energies and NA49 net proton data at SPS energies can be described reasonably well with a potential version of the Ur QMD in which mean-field potentials for both pre-formed hadrons and confined baryons are considered, with the help of a traditional coalescence afterburner in which one parameter set for both relative distance R_0 and relative momentum P_0,(3.8 fm, 0.3 Ge V/c), is used. Because of the large cancellation between the expansion in R_0 and the shrinkage in P_0 through the Lorentz transformation, the relativistic effect in clusters has little effect on the rapidity distribution of free(net) protons. Using a Woods-Saxon-like function instead of a pure logarithmic function as seen by FOPI collaboration at SIS energies, one can fit well both the data at SIS energies and the Ur QMD calculation results at AGS and SPS energies. Further, it is found that for central Au+Au or Pb+Pb collisions at top SIS, SPS and RHIC energies, the proton fractions in clusters are about33%, 10%, and 0.7%, respectively.展开更多
By considering different values of the time-step for the potential updates in the ultra-relativistic quantum molecular dynamics(UrQMD) model, we examine its influence on observables, such as the yield and collective f...By considering different values of the time-step for the potential updates in the ultra-relativistic quantum molecular dynamics(UrQMD) model, we examine its influence on observables, such as the yield and collective flow of nucleons and pions from heavyion collisions around 1 GeV/nucleon. It is found that these observables are affected to some extent by the choice of the time-step,and the impact of the time-step on the pion-related observables is more visible than that on the nucleon-related ones. However,its effect on the π-/π+yield ratio and elliptic flow difference between neutrons and protons, which have been taken as sensitive observables for probing the density-dependent nuclear symmetry energy at high densities, is fairly weak.展开更多
The time evolution of protons and 3He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 Ge V/nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics（Ur QMD） model...The time evolution of protons and 3He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 Ge V/nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics（Ur QMD） model combined with the traditional coalescence afterburner. In the coalescence process, the relative distance R0 and relative momentum P0 are surveyed in the range of 3-4 fm and 0.25-0.35 Ge V/c, respectively. For both clusters, a strong reversed correlation between R0 and P0is seen and it is time-dependent as well. For protons, the accepted（R0, P0） bands lie in the time interval 30-60 fm/c, while for 3He, a longer time evolution（at about 60-90 fm/c） is needed. Otherwise, much smaller R0 and P0values should be chosen. If we further look at the rapidity distributions from both central and semi-central collisions, it is found that the accepted [tcut,（R0, P0）] assemble can provide consistent results for proton yield and collective flows especially at mid-rapdities, while for 3He, the consistency is destroyed at both middle and projectile-target rapidities.展开更多
基金the National Natural Science Foundation of China(Grant Nos.11375062,11275068,11505056,and 11505057)the project sponsored by SRF for ROCS,SEM,the Education Bureau of Zhejiang Province(Grant No.Y201533176)the Doctoral Scientific ResearchFoundation(Grant No.11447109)
文摘A potential version of the UrQMD(UrQMD/M) transport model and a traditional coalescence model are combined to calculate the production of ~3He fragments in central Pb+Pb collisions at SPS energies 20-80 Ge V/nucleon. It is found that the Lorentz transformation in the afterburner influences visibly the ~3He yield and should be considered in calculations. The rapidity distribution of ~3He multiplicities(including the concave shape) can be described well with Ur QMD/M when it stops during t_cut=(100±25) fm/c and the coalescence afterburner with one parameter set of(R_0,P_0)=(3.8 fm, 0.3 Ge V/c) is taken into use afterwards.
基金the National Natural Science Foundation of China(Grant Nos.1137506211547312 and 11275068)+2 种基金the project sponsored by SRF for ROCSSEMand the Doctoral Scientific Research Foundation(Grant No.11447109)
文摘Rapidity distributions of both E895 proton data at AGS energies and NA49 net proton data at SPS energies can be described reasonably well with a potential version of the Ur QMD in which mean-field potentials for both pre-formed hadrons and confined baryons are considered, with the help of a traditional coalescence afterburner in which one parameter set for both relative distance R_0 and relative momentum P_0,(3.8 fm, 0.3 Ge V/c), is used. Because of the large cancellation between the expansion in R_0 and the shrinkage in P_0 through the Lorentz transformation, the relativistic effect in clusters has little effect on the rapidity distribution of free(net) protons. Using a Woods-Saxon-like function instead of a pure logarithmic function as seen by FOPI collaboration at SIS energies, one can fit well both the data at SIS energies and the Ur QMD calculation results at AGS and SPS energies. Further, it is found that for central Au+Au or Pb+Pb collisions at top SIS, SPS and RHIC energies, the proton fractions in clusters are about33%, 10%, and 0.7%, respectively.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11505057, 11547312, 11375062, and 11605270)the Department of Education of Zhejiang Province (Grant No. Y201533176)+1 种基金the China Postdoctoral Special Science Foundation (Grant No. 2016M591730)support by the computing server C3S2 in Huzhou University
文摘By considering different values of the time-step for the potential updates in the ultra-relativistic quantum molecular dynamics(UrQMD) model, we examine its influence on observables, such as the yield and collective flow of nucleons and pions from heavyion collisions around 1 GeV/nucleon. It is found that these observables are affected to some extent by the choice of the time-step,and the impact of the time-step on the pion-related observables is more visible than that on the nucleon-related ones. However,its effect on the π-/π+yield ratio and elliptic flow difference between neutrons and protons, which have been taken as sensitive observables for probing the density-dependent nuclear symmetry energy at high densities, is fairly weak.
基金supported by the National Natural Science Foundation of China(Grant Nos.11375062,11547312,11275068,11505056 and11505057)SRF for ROCS,SEM and the Doctoral Scientific Research Foundation(Grant No.11447109)
文摘The time evolution of protons and 3He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 Ge V/nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics（Ur QMD） model combined with the traditional coalescence afterburner. In the coalescence process, the relative distance R0 and relative momentum P0 are surveyed in the range of 3-4 fm and 0.25-0.35 Ge V/c, respectively. For both clusters, a strong reversed correlation between R0 and P0is seen and it is time-dependent as well. For protons, the accepted（R0, P0） bands lie in the time interval 30-60 fm/c, while for 3He, a longer time evolution（at about 60-90 fm/c） is needed. Otherwise, much smaller R0 and P0values should be chosen. If we further look at the rapidity distributions from both central and semi-central collisions, it is found that the accepted [tcut,（R0, P0）] assemble can provide consistent results for proton yield and collective flows especially at mid-rapdities, while for 3He, the consistency is destroyed at both middle and projectile-target rapidities.
