下面列出了团队人员在最近的科研工作中做的一些主要工作。下面的每篇文章均有详细介绍,点击即可。
Qingfeng Li et al., The isospin dependent nucleon–nucleon inelastic cross..., PLB 773, 557 (2017)
Yongjia Wang et al., Constraining the high-density nuclear..., PRC 89, 044603(2014).
Yongjia Wang et al., Collective flow of light particles in..., PRC 89, 034606 (2014).
Qingfeng Li et al., Ultrarelativistic quantum molecular...,PRC 85,034908(2012)
Caiwan Shen et al., Fusion hindrance in reactions ..., PRC 83,054620(2011)
Qingfeng Li et al.,Nonequilibrium dynamics ..., PRC 83, 044617(2011)
Junwen Mao et al., Diffusion over a fluctuating barrier..., PRE 83, 041108(2011)
Xiaolin Wang et al., Fusion hindrance in the..., Sci China Phys. Mech. Astron, 54, 472 (2011)


The isospin dependent nucleon–nucleon inelastic cross section in the nuclear medium

核介质中的同位旋依赖核子-核子非弹性散射截面

作者: Qingfeng Li, Zhuxia Li(李庆峰,李祝霞)

杂志: Physics Letters B 773 (2017) 557–562   

 DOI: https://doi.org/10.1016/j.physletb.2017.09.013

    摘要:本文在相对论BUU的框架下计算了核子-核子散射中能量、密度、以及同位旋依赖的Δ产生截面。这个截面的计算是考虑核子及Δ在同位旋不对称情况下质量劈裂的Born近似取得的。正是由于这些粒子的质量劈裂,结果表明,类似于核子-核子的弹性截面,在同位旋不对称的核介质中每一个特定电荷Δ粒子的出射道的截面介质约化效应均不同。而且,对于Δ++Δ-态出射而言,其效应最大且效果相反。本文所述方法结果也和不采用质量劈裂及采用DB方法计算的结果做了比较。并且,这种非弹散射截面的同位旋依赖性将会影响π+π-产额及相应比率的结果,因此,必将会对利用该比率探测高密区对称能软硬程度造成影响。

    Abstract: The calculation of the energy-, density-, and isospin-dependent Δ production cross sections in nucleon–nucleon (NN) scattering σ NNNΔ  has been performed within the framework of the relativistic BUU approach. The NΔ cross sections are calculated in Born approximation taking into account the effective mass splitting of the nucleons and  Δs in asymmetric matter. Due to the different mass splitting for neutron, proton and differently charged  Δs, it is shown that, similar to the NN elastic ones, the reductions of NΔ inelastic cross sections in isospin-asymmetric nuclear medium are different from each other for all the individual channels and the effect is largest and of opposite sign for the  Δ ++ and Δ states. This approach is also compared to calculations without effective mass splitting and with splitting derived from Dirac–Brueckerner (DB) calculations. The isospin dependence of the NΔ cross sections is expected to influence the production of π + and π mesons as well as their yield ratio, and thus affect the use of the latter quantity as a probe of the stiffness of the symmetry energy at supranormal densities.


Constraining the high-density nuclear symmetry energy with the transverse-momentum-dependent elliptic flow

利用横动量依赖的椭圆流约束对称能的高密行为

作者:Yongjia Wang, Chenchen Guo, Qingfeng Li, Hongfei Zhang, Y. Leifels, and W. Trautmann

杂志:Physical Review C 89, 044603 (2014)

       摘要:利用最近更新的极端相对论量子分子动力学模型,研究了400 MeV/nucleon金金碰撞中不同快度区间内自由核子的横动量依赖的椭圆流。发现中子-质子椭圆流的差和比敏感于对称能,特别是在大快度区间内中子-质子椭圆流的比。通过理论模拟与FOPI/LAND给出的横动量依赖的及积分的椭圆流数据比较,提取出对称能随密度的变化趋势接近于线性,这一结果与之前UrQMDQMD模型给出的结果相一致,而与目前有关文献中使用 pion-/pion+比给出的对称能的密度依赖行为结果不相同。

     Abstract: Within the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, the transverse-velocity dependence of the elliptic flow of free nucleons from Au+Au collisions at the incident energy 400 MeV/nucleon is studied within different windows of the normalized c.m. rapidity y0. It is found that the elliptic flow difference vn2 −vp2 and ratio vn2/vp2 of neutrons versus protons are sensitive to the density dependence of the symmetry energy, especially the ratio vn2/vp2 at small transverse velocity in the intermediate rapidity intervals 0.4<|y0|<0.6. By comparing either transverse-momentum-dependent or integrated FOPI/LAND elliptic flow data of nucleons and hydrogen isotopes with calculations using various Skyrme interactions, all exhibiting similar values of isoscalar incompressibility but very different density dependences of the symmetry energy, a moderately soft to linear symmetry energy is extracted, in good agreement with previous UrQMD or Tubingen QMD model calculations but contrast with results obtained with π−/π+ yield ratios in theliterature.


Collective flow of light particles in Au+Au collisions at intermediate energies

中能金金碰撞中轻质量碎片的集体流

作者:王永佳,郭琛琛, 李庆峰, 张鸿飞,李祝霞,Wolfgang Trautmann

杂志:Physical Review C89,034606 (2014)

   摘要:在极端相对论量子分子动力学模型中引入了Skyrme能量密度函数,用更新的模型研究了入射能量在150250400 MeV/nucleon的金金碰撞产生的轻质量碎片(质子、中子、氘核、氚核、3He4He)的直接流和椭圆流。模型模拟的结果与最新的FOPI实验数据进行了比对,发现轻质量碎片的产额、集体流可以被很好的再现。并且细致的研究了状态方程、介质修正的核核碰撞截面及碎片的构建方法对集体流的影响。发现轻质量碎片的集体流非常敏感于介质修正的核核碰撞截面,但不敏感于碎片的构建方法。还发现即便使用最新的实验数据和理论计算,仍然不能提取出更加精确的核物质不可压缩系数的范围。

       Abstract: The Skyrme potential energy density functional is introduced into the ultrarelativistic quantum molecular dynamics model and the updated version is applied to studying the directed and elliptic flows of light particles(protons, neutrons, deuterons, tritons, 3He, and4He) in Au+Au collisions at beam energies 150, 250, and 400 MeV/nucleon. The results are compared with the recent FOPI experimental data. It is found that the yields and collective flows of light particles can be described quite well. The influence of the equation of state, medium-modified nucleon-nucleon elastic cross sections (NNECS) and cluster recognition criteria on the directed and elliptic flows is studied in detail. It is found that the flows of light particles are sensitive tothe medium-modified NNECS, but not sensitive to the isospin dependent cluster recognition criteria. It seems difficult, however, even with the new data and calculations, to obtain a more accurate constraint on the nuclear incompressibility K0 than the interval 200–260 MeV.


Ultrarelativistic quantum molecular dynamics calculations of two-pion Hanbury-Brown–Twiss
correlations in central Pb-Pb collisions at √sNN = 2.76 TeV

利用极端相对论量子分子动力学模型计算LHC能量在2.76 TeV下的中心铅-铅碰撞后的两pion介子的HBT关联

作者:李庆峰, G. Graef (德国), M. Bleicher (德国)

杂志:Physical Review C 85, 034908 (2012)

  摘要:本文中我们利用一个微观的输运模型---极端相对论量子分子动力学模型---研究了最新LHC能区能量在2.76 TeV时中心铅-铅碰撞后的两pion介子的HBT关联。Pratt-Bertsch HBT半径的横动量依赖形式是通过把在径向协动系统内的关联子做一个三维的高斯拟合来抽取出来的。我们定性符合了LHC-ALICE的实验结果。但是,横向的R_O半径比实验值大了约50%。我们也将LHC能区的计算和实验结果同RHIC能区的STAR结果做了比较。在这两个能区中,我们均发现计算的R_O/R_S比值总是比实验值大,这意味着模型中的粒子出射强度没有实验观察到的猛烈。

   Abstract: Two-pion Hanbury-Brown–Twiss (HBT) correlations for central Pb-Pb collisions at the Large-Hadron-Collider (LHC) energy of√sNN = 2.76 TeV are investigated with the microscopic transport model ultrarelativistic quantum molecular dynamics. The transverse momentum dependence of the Pratt-Bertsch HBT radii is extracted from a three-dimensional Gaussian fit to the correlator in the longitudinal comoving system.Qualitative agreement with theALICE data is obtained, howeverRout is overpredicted by nearly 50%. The LHC results are also compared to data from the STAR experiment at RHIC. For both energies we find that the calculated RO : RS ratio is always larger than data, indicating that the emission in the model is less explosive than observed in the data.


Fusion hindrance in reactions with very heavy ions: Border between normal and hindered fusion

重离子反应中的熔合阻止:正常熔合和带有阻止熔合的边界

作者:沈彩万, D. Boilley(法国), 李庆峰,沈军杰,Y. Abe(日本)

杂志:Phys. Rev. C 83, 054620 (2011)

  摘要:利用双中心液滴模型,我们研究了重离子反应中的熔合阻止现象。结果显示,在重核从接触到复合核形成的过程中,颈部自由度和径向自由度可能会同时遇到由于内侧位垒引起的熔合阻止。通过系统计算,带有和不带有熔合阻止的反应被区别开来。计算表明,没有径向熔合阻止的反应数目远低于没有颈部熔合阻止的反应数目。并且对于这两种熔合阻止,非对称系数较大时所包含的无熔合阻止反应数大于非对称系数较小时所包含的熔合阻止数。对于复合核给定的反应,如果对应于某一非对称系数αc的反应不存在熔合阻止,则对所有非对称系数大于αc的反应也不存在熔合阻止。

   Abstract: The fusion hindrance in heavy-ion collisions is studied in the framework of the two-center liquid drop model. It appears that the neck and the radial degrees of freedom might both be hampered by an inner potential barrier on their path between the contact configuration to the compound nucleus. Heavy-ion reactions with and without the two kinds of fusion hindrance are classified through systematic calculations. It is found that the number of reactions without radial fusion hindrance is much smaller than that without neck fusion hindrance, and for both kinds of fusion hindrance the number of reactions without fusion hindrance at small mass-asymmetry parameter α is smaller than that at large α. In the formation of a given compound nucleus, if a reaction with αc is not hindered, then other reactions with α>αc are also not hindered, as is well known experimentally.


Nonequilibrium dynamics in heavy-ion collisions at low energies available at the GSI Schwerionen Synchrotron

GSI加速器低能区的重离子碰撞中的非平衡动力学

作者:李庆峰,沈彩万,郭琛琛,王永佳,李祝霞,J. Lukasik(波兰), W. Trautmann(德国)

杂志:Physical Review C 83, 044617 (2011)

  摘要:升级的极端相对论量子分子动力学模型(UrQMD),一个微观的输运模型,被用于研究入射能量在INDRA和低能FOPI实验区域的Au+Au碰撞后的直接、椭圆集体流及核阻止效应。很明显地,这些观测量不仅敏感依赖于状态方程(EOS)中的势能项(包括同位旋标量和同位旋适量部分,以及动量依赖项),也敏感于碰撞项(包括泡利阻塞和介质修正的核子-核子弹性散射截面(NNECS)).平均场势和密度依赖的NNECS的动量修正影响重离子碰撞的集体行为。在INDRA能区(<=150 MeV/nucleon),采用一个软的EoS+动量依赖及动量修正的密度依赖型NNECS的动力学输运能够很好地描述中心快度区出射的氢同位素(Z=1)的直接流数据。

   Abstract: The updated ultrarelativistic quantum molecular dynamics (UrQMD) model, a microscopic transport model, is used to study the directed and elliptic collective flows and the nuclear stopping in Au+Au collisions at incident energies covered by INDRA and lower-energy FOPI experiments. It is seen clearly that these observables are sensitive to both the potential terms (including isoscalar and isovector parts as well as the momentum dependent term) in the equation of state (EoS) and the collision term [including the Pauli blocking and the medium-modified nucleon-nucleon elastic cross section (NNECS)]. The momentum modifications of both, themean-field potentials and the density dependent NNECS, are found to affect the collectivity of heavy-ion collisions. At INDRA energies ( 150 MeV/nucleon) the dynamic transport with a soft EoS with momentum dependence and with the momentum-modified density-dependent NNECS describes the directed flow exhibited by hydrogen isotopes (Z = 1) emitted at midrapidity fairly well.


Diffusion over a fluctuating barrier in underdamped dynamics

  欠阻尼动力学系统跨越涨落势垒的扩散

作者:毛俊雯,沈彩万

杂志:Phys. Rev. E 83, 041108 (2011)

   摘要:本文从一个由加性噪声和乘性噪声驱动的朗之万方程出发,研究了欠阻尼动力学系统涨落势垒作用下的扩散性质。势垒的涨落由指数关联的高斯色噪声描述。本文给出了相关的一阶矩和二阶矩的解析解。更进一步地,通过直接模拟的方法计算得到了布朗粒子越过涨落势垒的渐进概率。结果表明涨落的关联性在跨越势垒动力学问题中起着重要作用。

      Abstract: We apply a Langevin model by imposing additive and multiplicative noises to study thermally activated diffusion over a fluctuating barrier in underdamped dynamics. The barrier fluctuation is characterized by Gaussian colored noise with exponential correlation. We present the exact solutions for the first and second moments. Furthermore, we use direct simulations to calculate the asymptotic probability for a Brownian particle passing over the fluctuating barrier. The results indicate that the correlation of the fluctuating barrier is crucial for barrier crossing dynamics.


Fusion hindrance in the neck evolution of symmetric nuclear reactions

对称反应中颈部演化的熔合阻止

作者:王小琳,沈彩万,李庆峰,刘玲

杂志:Science China G 54, 470-473 (2011)

      摘要:在重核反应中的径向自由度的熔合阻止已经为大家所了解很长一段时间了。然而本文将说明,熔合阻止在颈部熔合中也同样存在。我们用双中心液滴模型计算不同径向值和不同颈部系数时的势能,然后通过计算势能对颈部系数在右端点(e=1)时的导数来确定颈部熔合阻止的存在性问题。利用这种方法系统计算了熔合阻止在对称反应时的存在区域。

     Abstract: Fusion hindrance in the radial degree of freedom for massive nuclear reactions is known for a long time. However the present work shows that the fusion hindrance also exists in the neck evolution. We calculate the potential at different distances and different neck parameters by the two-center liquid drop model and then check whether fusion hindrance exists in the neck evolution by examing the sign of slope of potential vs. the neck parameter. The area of fusion hindrance in the neck evolution is shown.