LHC-ALICE实验5.02TeV铅核-铅核对撞中瞬发与非瞬发J/ψ产生的研究

相对论重离子对撞的一个主要目的是研究在非常高的温度和能量密度下解禁闭的夸克胶子等离子体QGP的性质。重夸克主要通过碰撞早期的部分子硬散射产生，然后穿过QGP的整个演化过程，因此被认为是研究QGP的理想探针。由正反粲夸克组成的夸克偶素J/ψ在QGP中的产生和输运过程，是当前高能核物理的研究热点。J/ψ从产生的过程可以分为瞬发和非瞬发。瞬发J/ψ来自于碰撞早期的直接产生和粲夸克偶素激发态的衰变，产额对QGP介质中解离和重组合过程敏感，测量瞬发J/ψ对于研究J/ψ的解离和重组合机制至关重要。非瞬发J/ψ来自于底夸克强子的衰变，产额不会受到解离和重组合的影响，因此非瞬发J/ψ可以作为更加直接的探针研究底夸克穿过QGP的能量损失。本研究拟利用ALICE5.02TeV铅核-铅核对撞的数据测量瞬发和非瞬发J/ψ在中心快度区的产额和核修正因子,本项目利用了机器学习的方法提高J/ψ的重建效率。

The primary motivation of the heavy-ion collisions is to study the properties of the matter with high temperature and energy density, Quark-Gluon Plasma(QGP). Heavy quarks are produced via the initial hard scatterings in the earlier stage. It carries the full information of the QGP involution. Therefore, they are suggested as excellent probes to investigate the QGP. J/ψ is the charm and anti-charm quarks hidden states, which can be divided into prompt and non-prompt two components based on its production mechanism. The prompt J/ψ are sensitive to the QGP-induced dissociation and re-generation effects. Measurement of the prompt J/ψ is crucial to understand the J/ψ dissociation and re-generation production mechanism. The non-prompt J/ψ are from the bottom hadrons decay, the lifetime of the bottom hadrons is much longer than the QGP. Therefore, the non-prompt J/ψ are the direct probe to study the bottom quark energy loss in the QGP. This project is the measurement of the non-prompt and prompt J/ψ production and nuclear modification factors in Pb-Pb 5.02 TeV collision with the ALICE experiment at mid rapidity in LHC. The machine learning approach will be used to improve the J/ψ reconstruction efficiency.