LHC/ALICE实验重夸克能量损失与集体效应研究

We measure muon spectrum produced in lead-lead collisions at 2.76TeV and 5.52 TeV with ALICE at the LHC and separate the muon components from charmed and bottom quark and w boson decay as well as subtract pi/k backgrounds.The muon spectrum from W boson decay is taken as the reference to scale heavy quark energy loss for the W boson dose not participate in the strong interaction. The heavy quark energy loss scaled by W decay muons is compared with those scaled by nuclear modification factor to deeply study the heavy quark energy loss mechanism. The double ratioes of charm and bottom quark energy loss is measured to test pQCD prediction and Ads/CFT picture.The elliptic flow of muons from open heavy flavor decays is measured to study the thermalized characteristics of the heavy quarks in QGP as well as to obtain thermodynamical and initial state information of the QCD medium in low pt region.The elliptic flow parameters in high pt region are studied to extract the information of the path length dependence of heavy quark energy loss in medium. The evolution of the initial energy density with rapidity for the QGP system is revealed by comparing the heavy quark elliptic flow measured in forward rapidity region with those in central rapidity region. Nuclear modification factor of W bosons is meaured to detect the modified parton distribution function in nuclear and cold nuclear effects. The modification factor of muon transverse momentum in proton-lead collisions at 5.02 TeV is observed to study cold nuclear effect in initiate state, like nuclear shadowing, k_T broadening and Bremsstrahlung effect, to provide inspection of the CGC mater state model and reference for nucleus-nucleus collisions.

)：参加ALICE实验,测量2.76TeV和5.5TeV铅-铅碰撞中的muon谱，分离粲、底夸克和W 玻色子衰变组分和pi/k背景。利用W 玻色子不参与强作用特性标度重夸克能量损失，比较核修正因子标度重夸克能量损失的差异，研究重夸克能量损失机制。测量粲、底夸克能量损失比值，检验pQCD和Ads/CFT预言。测量重夸克衰变muon椭圆流，研究低横动量区间重夸克在热密介质中的热化特性，获得碰撞系统热力学和初态信息；研究高横动量区间椭圆流参数，提取重夸克能量损失对路径长度依赖信息。比较向前区和中心区重夸克椭圆流，研究QGP系统初始能量密度随快度的演化。揭示重夸克集体运动性质和热密物质性质。测量W玻色的核修正因子，研究核修正的部分子分布函数。测量5.02TeV 质子-铅核碰撞的muon谱及其横动量修正因子RpA，检测冷核初态核遮蔽、横动量加宽和韧致辐射效应，提供检验CGC模型参考和核核碰撞参考。

课题组按计划完成了项目研究计划与任务，在夸克物质的硬探针（重夸克及高横动量粒子）信号及其性质，夸克物质集体运动性质，小碰撞系统末态效应及冷核效应研究上取得了重要进展。课题组总共发表SCI论文17篇，其它论文5篇。其中，代表ALICE合作组发表SCI论文9篇；代表合作组发表重要国际会议论文集论文9篇，其中是SCI论文4篇；发表与此相关唯象理论SCI论文4篇；发表探测器及电子学SCI论文1篇。还发表ALICE物理分析内部文档18篇。此外，还与ALICE国际合作组共享论文106篇。主办国际会议5次；在国际会议上作邀请报告14个，国内会议邀请报告18个，国际会议墙报6个。培养博士生5名，硕士生6名，博士后2名，博士毕业生和博士出站均就业于中国高校或科研院所。从国外引进青年优秀人才2名。课题组1人次被遴选为ALICE合作组常务管理委员会成员，1人被遴选为ALICE物理分析组召集人，1人被遴选为CERN Scientific Associate。. 在向前区首次观测到重味强子在大横动量区间存在明显压低，揭示底夸克存在很强的能量损失。在中心区观测到轻味中性粒子产额显著压低至8-10倍，揭示轻味夸克存在更强的能量损失。首次拓展双强子关联产额压低因子测量到低横动量区间，观测到关联产额的显著增强，表明高能部分子穿越QGP物质损失的能量转化成大量低能粒子。最先把向前区冷核效应观测推向更小xB区间（10-6 - 10-2)，证实重夸克衰变μ子产额显著压低源于重夸克穿越热密物质大幅损失能量所致，证实TeV能区铅核碰撞生成了夸克胶子等离子体。在向前区首次观测到中等横动量区间重味夸克椭圆流，表明重味夸克与热密物质存在很强的相互作用并参与热密物质集体运动，暗示重夸克可能亦被热化。在LHC能区首次观测到（多）奇异重子的椭圆流，在低横动量区间，椭圆流遵从质量排序，能够被粘滞流体力学模型所描述；在中等横动量区，首次观测到（多）奇异重子椭圆流的夸克数目标度性破坏~20%，表明强子相的贡献不可忽略。这些研究成果对认识夸克物质的形成机制、揭示夸克物质的性质和演化规律具有重要的意义。