Quenching and flow of charm and bottom quarks via semi-leptonic decay of D and B mesons in Pb+Pb collisions at the LHC

Heavy flavor particles provide important probes of the microscopic structure and thermodynamic properties of the quark-gluon plasma(QGP)produced in high-energy nucleus-nucleus collisions.We studied the energy loss and flow of charm and bottom quarks inside the QGP via the nuclear modification factor(R_(AA))and elliptic flow coefficient(v_(2))of their decayed leptons in heavy-ion collisions at the LHC.The dynamical evolution of the QGP was performed using the CLVisc(3+1)-dimensional viscous hydrodynamics model;the evolution of heavy quarks inside the QGP was simulated with our improved Langevin model that considers both collisional and radiative energy loss of heavy quarks;the hadronization of heavy quarks was simulated via our hybrid coalescence-fragmentation model;and the semi-leptonic decay of D and B mesons was simulated via PYTHIA.Using the same spatial diffusion coefficient for charm and bottom quarks,we obtained smaller R_(AA) and larger v_(2) of charm decayed leptons than bottom decayed leptons,indicating stronger energy loss of charm quarks than bottom quarks inside the QGP within our current model setup.

A discussion on the anomalous threshold enhancement of J/ψ–ψ(3770)couplings and X(6900)peak

The attractive interaction between J/ψandψ(3770)has to be strong enough if X(6900)is of the molecule type.We argue that sinceψ(3770)decays predominantly into a DD^(¯)pair,the interactions between J/ψandψ(3770)may be significantly enhanced owing to the three point DD^(¯)loop diagram.The enhancement originates from the anomalous threshold located at t=−1.288 GeV^(2),whose effect propagates into the s-channel partial wave amplitude in the vicinity of √s≃6.94 GeV.This effect may be helpful in the formation of the X(6900)peak.

通过相对论重粒子碰撞中的J/ψ产生揭秘胶子喷注淬火机制

长久以来,喷注淬火被认为是探测重离子碰撞中形成的夺克胶子等离子体的关键信号之一,尽管过去在喷注火研究方面已经付出了巨大的努力、但是区分夸克和胶子的喷注淬火仍然是一个非常大的挑战本文发现大横动量J/主要由胶子碎裂产生,因此为探测胶子在热密介质中的能量损失提供了一个独特的敏感探针,作者首先基于领头幂次的NRQCD因子化理论计算了质子-质子碰撞中的大横动量J/产生,发现胶子碎裂是大横动量J/产生的主要机制,然后通过线性玻尔兹曼输运模型和相对论流体力学模拟了核-核碰撞中喷注与热密介质的相互作用,所得数值结果很好地描述了大横动量J/的核修正因子和椭圆流,揭示出胶子能量损失是大横动量J/产额压低的主要机制。作者进一步通过数据驱动的贝叶斯分析方法证实了这个新颖的结论,并定量提取出夸克胶子等离子体中的胶子能量损失分布。

Physics perspectives of heavy-ion collisions at very high energy

Heavy-ion collisions at very high colliding energies are expected to produce a quark-gluon plasma(QGP) at the highest temperature obtainable in a laboratory setting. Experimental studies of these reactions can provide an unprecedented range of information on properties of the QGP at high temperatures. We report theoretical investigations of the physics perspectives of heavy-ion collisions at a future high-energy collider. These include initial parton production, collective expansion of the dense medium, jet quenching,heavy-quark transport, dissociation and regeneration of quarkonia, photon and dilepton production. We illustrate the potential of future experimental studies of the initial particle production and formation of QGP at the highest temperature to provide constraints on properties of strongly interaction matter.

Heavy flavor quenching and flow:the roles of initial condition,pre-equilibrium evolution,and in-medium interaction

Within an advanced Langevin-hydrodynamics framework coupled to a hybrid fragmentation-coalescence hadronization model,we study heavy flavor quenching and flow in relativistic heavy-ion collisions.We investigate how the initial heavy quark spectrum,the in-medium energy loss and hadronization mechanisms of heavy quarks,the evolution profile of the pre-equilibrium stage,the medium flow,and the temperature dependence of heavy quark diffusion coefficients influence the suppression and elliptic flow of heavy mesons at the RHIC and the LHC.Our results show that the different modeling of initial conditions,pre-equilibrium evolution,and in-medium interactions can individually yield uncertainties of approximately 10-40% in D meson suppression and flow at a low transverse momentum.We also find that proper combinations of collisional versus radiative energy loss,coalescence versus fragmentation in hadronization,and the inclusion of medium flow are the most important factors for describing the suppression and elliptic flow of heavy mesons.