冷核物质J/ψ产生过程中粲夸克的能量损失效应

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 can give an important tool for clarifying the conventional nuclear suppression mechanism in heavy-ion collisions. We will deeply explore the physical mechanisms for J/ψ production in cold nuclear matter, distinguish the case with J/ψ formation occurring outside the nucleus and the case with occurring inside the nucleus by J/ψ formation time, the beam energy as well as the nuclear size, so then quantitatively distinguish the influence of the two final-state nuclear effects (energy loss and nuclear absorption ) on the attenuation of the J/ψ production; by means of accurately calculating the path length of the charm-quark pair in the nucleus , we will improve the nuclear modification model due to quark energy loss which has been used in our previous work; by the global fit of the selected corresponding experimental data with different beam energy and with J/ψ production occurring outside the nucleus，we will extract the value of the charm quark energy loss and compare it with the value of the light quark energy loss obtained by fitting the experimental data about the semi-inclusive deep inelastic scattering. In addition, by means of the J/ψ production experimental data, we will study the energy loss of high energy gluon traveling in the cold nuclear matter, which can not be explored in our preceding work by means of the nuclear Drell-Yan process. The obtained results in this present work will give an enlightenment on the study about the energy loss effect in hot nuclear matter from heavy-ion collisions.

高能重粒子碰撞热核环境中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。本项目将深入研究冷核物质中J/ψ产生的物理过程，根据J/ψ形成时间以及具体入射能量和靶核尺度，区分J/ψ在核外、核内形成的不同情况，进而定量区分能量损失和核吸收两种末态核效应对J/ψ产额的压低影响；通过精确计算粲夸克对在靶核中的传播路径，改进之前研究中夸克能量损失的核修正模型；对代表J/ψ在核外形成的不同入射能量的所有实验数据进行整体拟合，获取粲夸克的能量损失值并与先前半举深度非弹性散射中获得的轻夸克的能量损失进行比较研究。本项目还将借助J/ψ产生的实验数据，分析以前对核Drell-Yan过程研究中无法得到的高能胶子在冷核中能量损失的相关信息。本项目研究结果将促进重粒子碰撞热核环境中能量损失效应的理论研究。

研究背景：. 来自 LHC 的关于重离子碰撞的大量实验数据, 清楚地反映了J/ψ粒子产额压低的现象。由于在高能重离子碰撞形成的高热高密核物质中存在许多复杂的核效应，研究质子-原子核碰撞中冷核物质对J/ψ粒子生成过程的影响，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。.研究内容：.1、质子-原子核碰撞J/ψ粒子产生过程中的核效应.2、末态粲夸克对在靶核中传播时能量损失效应的核修正.3、比较研究重夸克和轻夸克在冷核物质中能量损失的参数值.重要结果：.1、当J/ψ粒子在靶核外形成时，粲夸克对的能量损失效应是造成J/ψ粒子产额压低的主要末态核效应，获得粲夸克对单位长度能量损失的平均值为：2.97±0.74GeV/fm。.2、初态入射夸克的能量损失效应, 在较大的动量区间对J/ψ粒子产额压低的影响较大, 入射胶子的能量损失效应在较小的动量区间影响较大; 入射夸克能量损失效应在反应能量较高(如LHC,RHIC)时, 可以忽略。.3、获得入射胶子单位长度能量损失的平均值为 2.18±0.14 GeV/fm，与由于胶子的强耦合作用胶子的能量损失值大于夸克的理论预言一致。.4、借助轻子-原子核碰撞半举深度非弹性散射过程，获得了出射轻夸克能量损失的传递系数。.5、借助核Drell-Yan过程，获得了入射轻夸克能量损失的传递系数。.6、考虑质子-原子核碰撞J/ψ粒子产生过程中粲夸克对在靶核中传播路径的几何效应，采用描述重夸克能量损失的权重函数，获得了粲夸克能量损失的传递系数。验证了重夸克的能量损失小于轻夸克的理论预言。.科学意义：. 寻找和发现夸克胶子等离子体这一新物质形态是本世纪中高能核物理理论和实验研究的核心问题。 本项目所取得的研究结果将有助于准确理解高能部分子在冷核物质中的传播及能量损失效应，进而促进高能核-核碰撞过程中快夸克在高热高密核物质中传播时能量损失的理论研究，更好地理解高能重离子碰撞J/ψ粒子产生的实验数据，从而获取夸克胶子等离子体形成的确切信息。