RHIC和SPS上QGP强子化机制的研究

Hadronization is an important issue in non-purtubativie quantum chromodynamics (QCD). In relativistic heavy ion collisions, it is a key bridge between final-state observables and the quark gluon plasma (QGP) produced in early stage of collisions. RHIC physics show that the quark combination mechanism plays an indispensable role in the hadronization of QGP. Recently the Beam Energy Scan program of STAR Collaboration and SPS experiments at CERN found many new features of hadron production in heavy ion collisions in the low BES energy range 5-20GeV, e.g. the rule of quark number scaling for hadronic elliptic flow v2 is broken partially as the collision energy decreases to 11.5 GeV. Is the quark combination mechanism applicable in this energy region? Is QGP created? In this project, we will apply a quark combination model developed by Shandong Group to systematically study the production of various thermal hadrons, in particular, that of the strange hadrons and resonances in heavy ion collisions in the entire BES energy range(5-200 GeV). We shall investigate collective flows, baryon-antibaryon and baryon-strangeness correlation, event-by-event fluctuation of hadronic yields and yield ratios between different species of hadrons, effects of hadronic rescattering on hadron production, in particular on resonance production, to test the universality of quark combination mechanism and explore the creation threshold of QGP and the feature of phase transition at lower collisional energies.

强子化是强相互作用理论的基本问题，也是相对论重离子碰撞中夸克胶子等离子体(QGP)与末态观测量联系的关键。RHIC 物理研究表明：夸克组合是QGP 强子化的必要机制。最近，STAR的能量扫描实验和SPS实验在碰撞质心能量5-20GeV的能区上发现了强子产生的新特征，如强子椭圆流的组分夸克数标度性破缺。此能区夸克组合是否仍然适用? QGP新物质态是否产生？本项目将利用山东夸克组合模型对碰撞能量5-200GeV的重离子碰撞中热强子尤其是奇异强子和共振态的产生规律进行系统研究。通过对集体流、重子-反重子关联、重子-奇异数关联等关联量、强子的产额和产额比的事件涨落以及强子重散射对强子产生特别是共振态产生的影响的研究，检验夸克组合机制的普适性，深入理解强子化规律，探索较低能区QGP的产生阈以及相变特征。

强子化是强相互作用理论的基本问题，也是相对论重离子碰撞中夸克胶子等离子体(QGP)与末态观测量联系的关键。本项目利用山东夸克组合模型描述相对论重离子碰撞中QGP物质的强子化过程，系统研究了中小横动量强子的产生性质。结合LHC实验，着重研究了SPS和RHIC能区上奇异强子和共振态的产生。考虑强子重散射效应，成功解释了质心能量为19.6, 62.4, 200, 2760GeV的重离子碰撞中phi和K^* (892)横动量谱的实验数据，表明了夸克组合机制可以描述强子化时共振态强子的产生，并预言了Σ^* (1385)和Ξ^* (1530)的横动量谱。研究了含有粲夸克的单粲强子的产生，给出能够检验粲夸克和轻夸克组合动力学特征的特色预言。研究了奇特态hidden-charm五夸克态P_c^+ (4380),P_c^+ (4450)在强子化时的产生并预言了在相对论重离子碰撞中的产额。以重子数-奇异性关联为例，研究了强子化时系统守恒荷关联的改变。唯象计算结果重复了格点QCD在奇异解禁闭相变温度处的数值计算结果。提出了一个新的两粒子快度关联函数，将两强子关联和强子化前的夸克关联函数直接联系起来，给出了既能检验强子化机制又能抽取夸克快度关联信息的特色预言。研究了强子化导致的强子多重数涨落和关联，并在考虑强子化前夸克的关联涨落和共振态衰变后提出一系列的新奇的观测信号。结合现有实验数据，以上研究表明夸克组合机制能够有效地描述不同碰撞能量下各种强子的产生。将本项目的理论预言与未来的实验数据比较，能更深入地检验夸克组合机制和理解强子化规律。