高能夸克在核环境中的能量损失

利用夸克能量损失公式和从轻子-原子核深度非弹性散射实验数据得到的束缚核子中的部分子分布函数,计算了FNAL E866 800 GeV的质子打击不同原子核的Drell-Yan过程截面比,发现考虑能量损失的计算结果与FNAL E866实验数据符合甚好.建议在利用核Drell-Yan过程实验数据抽取束缚核子内部分子分布函数时考虑能量损失效应.     

核Drell-Yan过程与部分子分布的不均匀性

通过p-A碰撞的核Drell-Yan过程研究了核遮蔽效应及其空间相关性.对末态轻子对的观测反映了相互作用点的情况.计算了能量为800 GeV的质子打击Ca,W,Au核的Drell-Yan过程与p-p碰撞Drell-Yan过程的微分截面比.研究发现,在考虑部分子分布的空间依赖性后,核Drell-Yan的截面会有显著变化.计算结果与未来精确测量p-A碰撞核Drell-Yan过程的实验数据比较,能够定量地验证部分子分布函数的空间依赖性.     

The dependence of J/ψ-nucleon inelastic cross section on the Feynman variable

By means of two typical sets of nuclear parton distribution functions, meanwhile taking account of the energy loss of the beam proton and the nuclear absorption of the charmonium states traversing the nuclear matter in the uniform framework of the Glauber model, a leading order phenomenological analysis is given in the color evaporation model of the E866 experimental data on J/ψ production differential cross section ratios R_Fe/Be(x_F). It is shown that the energy loss effect of beam proton on R_Fe/Be(x_F) is more important than the nuclear effects on parton distribution functions in the high Feynman variable x_F region. It is found that the J/ψ-nucleon inelastic cross section depends on the Feynman variable x_F and increases linearly with x_F in the region x_F>0.2.     

电子-电子相互作用对trion静态性质的影响

基于一维紧束缚SSH模型和扩展的Hubbard模型,采用非绝热分子动力学方法,在非限制性Hartree-Fock(HF)平均场近似下,研究了三粒子复合体trion的静态性质.trion比极化子、双极化子具有更大的束缚能、稳定性和有效质量;电子-声子耦合和电子间相互作用均增强trion的局域度,并导致其有效质量增大,稳定性增强.     

高能碰撞J/ψ粒子的产生与能量损失效应

根据色蒸发产生机制、应用能量损失的上限值计算了RHIC和HERA上J/ψ粒子产生中核效应α的xF分布,并与实验数据进行了对比.研究表明:给定初态能量损失上限,较之HERA的结论,RHIC的计算与实验吻合更好,反映出后者的末态效应较弱.加入末态效应后均有所改观,表明解释J/ψ粒子产值的抑制还需要考虑其它的介质效应.     

粲夸克对在质子-原子核碰撞J/ψ 产生过程中的能量损失

高能重离子碰撞热核环境中J/ψ产额的压低被认为是夸克胶子等离子体生成的重要信号。研究冷核物质中各种核效应对J/ψ 形成过程的影响,是准确理解热核环境中核效应对J/ψ产额压低机制的重要途径。研究了质子-原子核碰撞J/ψ 产生过程中初态部分子分布函数的核效应、入射质子的能量损失效应、以及末态粲夸克对能量损失效应对J/ψ 粒子产额的压低作用,对质子-原子核碰撞J/ψ产生过程的微分截面比R_Fe/Be(xF)进行了领头阶的唯象分析,并与E866 实验数据中代表J/ψ粒子在靶核外产生的实验数据进行比较,获取了粲夸克对的能量损失值(3.81±1.71) GeV/fm。研究结果表明,部分子分布函数的核效应对截面比RFe=Be(xF) 的压低作用在xF > 0区域是随着xF 的增大而增大的;末态粲夸克对的能量损失效应是影响J= 粒子产额压低的重要核效应;当xF较大时(0:65≤xF≤0.92),初态入射质子的能量损失效应在对微分截面比R_Fe/Be(xF)的压低中起了主要作用。J/ψ suppression observed in hot nuclear matter from heavy-ion collisions is considered as a most reliable signature for the formation of Quark-Gluon Plasma. The study about the nuclear effects on J/ψ production in cold nuclear matter provides an important tool for clarifying the conventional nuclear suppression mechanism in heavy-ion collisions. J/ψ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution, the energy loss of beam proton in initial state, and the finial state energy loss of c¯c pair.The leading-order computations for J/ψ production cross-section ratios RFe=Be(xF) are presented and compared with the selected E866 experimental data with the J/ψ production occurring outside the nucleus, the obtained energy loss of the color octet is (3.81±1.71) GeV/fm. It is found that the nuclear suppression from the nuclear effects on the parton distribution functions becomes larger as the increase of xF in the range xF > 0,the J/ψ suppression on R_Fe/Be(xF) induced by the energy loss of color octet c¯c is an important nuclear effect, in the region 0:656xF 60:92, the energy loss of beam proton in initial state is the dominant mechanism which causes a reduction of the J/ψ yield.     

Energy loss of charm quarks from J/ψ production incold nuclear matter

J/ψ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution, energy loss of beam proton and the finial state energy loss of color octet cc. The leading-order computations for J/ψ production cross-section ratios R_W/Be(x_F) are presented and compared with the selected E866 experimental data with the cc remaining colored on its entire path in the medium. It is shown that the combination of the different nuclear effects accounts quite well for the observed J/ψ suppression in the experimental data. It is found that the J/ψ suppression on R_W/Be(x_F) from the initial state nuclear effects is more important than that induced by the energy loss of color octet cc in the large x_F region. Whether the cc pair energy loss is linear or quadratic with the path length is not determined. The obtained cc pair energy loss per unit path length α=2.78±0.81 GeV/fm, which indicates that the heavy quark in cold nuclear matter can lose more energy compared to the outgoing light quark.     

Energy loss of charm quarks from J/ψ production in cold nuclear matter

J/ψ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution,energy loss of beam proton and the finial state energy loss of color octet cc. The leading-order computations for J/ψproduction cross-section ratios RW/Be(x F) are presented and compared with the selected E866 experimental data with the cc remaining colored on its entire path in the medium. It is shown that the combination of the different nuclear effects accounts quite well for the observed J/ψ suppression in the experimental data. It is found that the J/ψ suppression on RW/Be(x F) from the initial state nuclear effects is more important than that induced by the energy loss of color octet cc in the large x F region. Whether the cc pair energy loss is linear or quadratic with the path length is not determined. The obtained cc pair energy loss per unit path length α = 2.78±0.81 Ge V/fm, which indicates that the heavy quark in cold nuclear matter can lose more energy compared to the outgoing light quark.