Dynamical magnetic enhancement of light and heavy quark jet quenching at RHIC

A new Monte Carlo implementation of Djordjevic?s dynamical scattering generalization of the DGLV radiative energy loss opacity series is used with a hybrid interpolation scheme to compute both light and heavy quark jet quenching up to third order in opacity. The enhancement of the ratio of bottom to charm quark energy loss due to perturbative long range color magnetic effects in nonuniform Bjorken expanding geometries is found to reduce the significance of the heavy quark jet puzzle posed by the observed near equality (within sizeable errors) of pion and nonphotonic electron nuclear modification at RHIC. Jet Flavor Spectroscopy discussed below will be a powerful tool to differentiate competing dynamical models of the QGP produced in ultra-relativistic nuclear collisions.     

Relativistic correction to the dissociation temperature of Bc mesons in a hot medium

By solving two body Dirac equations with potentials at finite temperature, we calculate the dissociation temperature begin{document}$ T_d $end{document} of begin{document}$ B_c $end{document} mesons in quark-gluon plasma. It is found that begin{document}$ T_d $end{document} becomes higher with the relativistic correction than the begin{document}$ T_d $end{document} from the Schr?dinger equation. Both the short range interaction and the constant term of the potential at the long-range scale have a contribution to the shift of begin{document}$ T_d $end{document}, while the spin interaction is negligible.     

介质对部分子劈裂几率的影响

利用部分子在热密QCD介质中的辐射谱, 研究部分子在热密介质中的演化规律. 研究结果表明, 在相同能量下介质诱导效应使得部分子在介质中的劈裂几率大于部分子在真空中的劈裂几率; 高密度介质中的部分子劈裂几率大于低密度介质中的劈裂几率. 本文研究结果与美国BNL/RHIC相对论重离子碰撞实验中观测到的高横动量强子产额压低现象一致, 揭示了在RHIC能区已经生成高温高密物质.     

Jet-photon conversion with energy loss in heavy ion collisions

The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √S＝ 200 AGeV, and by about 80% at LHC with √S = 5500 AGeV.     

Jet-photon conversion with energy loss in heavy ion collisions

The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √8= 200 AGeV, and by about 80% at LHC with √8 = 5500 AGeV.     

粲夸克辐射的死区效应

基于轻夸克辐射能量谱, 考虑夸克质量对部分子辐射能量损失的影响, 利用死区因子把轻部分子辐射能量损失谱推广到重部分子辐射能量损失的情形. 研究结果表明, 利用与夸克质量相关的死区因子推广轻夸克辐射能量损失谱得到的重夸克辐射能量损失谱, 与直接利用微扰QCD计算所得到的Djordjevic-Gyulassy(D-G)谱的结果一致, 且极大简化了重夸克辐射能量损失的计算.     

Interactions between heavy quarks and tilted QGP fireballs in 200 A GeV Au+Au collisions

Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor (begin{document}$R_{AA}$end{document}) and directed flow (begin{document}$ v_1 $end{document}) and elliptic flow (begin{document}$ v_2 $end{document}) coefficients of heavy mesons and their decayed electrons at an RHIC energy. We find that the counter-clockwise tilt of nuclear matter in the reaction plane results in a positive (negative) heavy flavor begin{document}$ v_1 $end{document} in the backward (forward) rapidity region, whose magnitude increases with the heavy quark transverse momentum. The difference in the heavy flavor begin{document}$R_{AA}$end{document} between different angular regions is also proposed as a complementary tool to characterize the asymmetry of the medium profile. Our model results are consistent with currently available data at the RHIC and provide predictions that can be tested by future measurements.     

Gluon Propagator and Heavy Quark Potential in an Anisotropic QCD Plasma

The hard-loop resummed propagator in an anisotropic QCD plasma in general linear gauges are computed. We get the explicit expressions of the gluon propagator in covariant gauge, Coulomb gauge and temporal axial gauge. Considering one gluon exchange, the potential between heavy quarks is defined through the Fourier transform of the static propagator. We find that the potential exhibits angular dependence and that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment.     

Flavor-dependent photoproduction in heavy-ion collisions

Strong electromagnetic fields produced in the non-central heavy-ion collisions can induce vector meson photoproduction. In this paper, we study the photoproduction J/ψ and φ mesons in the relativistic heavy-ion collision from ultra-peripheral nuclear collisions to peripheral hadronic heavy ion collisions. And then include both initial hadronic production and thermal production in quark-gluon plasma (QGP). We find, for the charm anti-charm bound state J/ψ, the photoproduced J/ψs are mainly in the very low momentum region and clearly exceed the hadronic production. However, considering the thermal production of strange quark anti-quark pairs in QGP produced in relativistic heavy-ion collisions, the photoproduced φ is usually smaller than the thermal production and only evident at very peripheral collisions as even their photoproduction is much larger than J/ψ.     

超高能诱发核反应的国际合作实验研究进展

综述超高能诱发核反应的国际合作实验进展及相关的重离子物理研究现状.内容包括:1.有关夸克物质(夸克胶子等离子体QGP)的理论预言.2.超高能重离子碰撞的实验:(1)BNL/AGS能区的固定靶实验回顾;(2)CERN/SPS能区的固定靶实验回顾;(3)BNL/RHIC能区的对撞实验现状;(4)CERN/LHC能区的对撞实验现状.     

依赖系统大小的能量损失对强子谱压低的影响

基于微扰量子色动力学(pQCD)的部分子模型, 在领头阶(LO)近似下分别计算了质子－质子(p+p)碰撞, Au+Au和Cu+Cu不同对心度碰撞产生π⁰的强子谱和相应的核修正因子R_AA. 在考虑部分子喷注能量损失(即喷注淬火)效应后的理论计算表明, 与相同质心系能量s=200GeV的p+p碰撞相比, Au+Au或Cu+Cu不同对心度碰撞产生的强子谱被压低, 被压低的程度与依赖系统大小的能量损失有强烈的关系. 系统越大, 部分子喷注的能量损失越大, 导致强子谱被压低得越多, R_AA越小. 理论计算的数值结果和实验数据相符合, 说明能量损失机制的可靠性和真实性.     

在近平衡态QGP中费米子的分布函数

从QGP动力论出发,得到QGP在色场涨落扰动下偏离平衡态而处于近平衡时的分布函数, 进而分析了决定偏离因子的物理因素.并分别讨论了在高温低密和低温高密区偏离因子特征.     

中能区重离子碰撞中径向膨胀能量研究

在Skyrme相互作用下讨论了径向膨胀能量对平均场、核子-核子碰撞截面的依赖关系,得到了有关状态方程的信息.在计算中发现,中能区重离子碰撞中径向膨胀能量受平均场影响较大,而截面对它的影响很小.     

Hubble parameter in QCD Universe for finite bulk viscosity

We consider the influence of the perturbative bulk viscosity on the evolution of the Hubble parameter in the QCD era of the early Universe. For the geometry of the Universe we assume the homogeneous and isotropic Friedmann‐Lemaitre‐Robertson‐Walker metric, while the background matter is assumed to be characterized by barotropic equations of state, obtained from recent lattice QCD simulations, and heavy‐ion collisions, respectively. Taking into account a perturbative form for the bulk viscosity coefficient, we obtain the evolution of the Hubble parameter, and we compare it with its evolution for an ideal (non‐viscous) cosmological matter. A numerical solution for the viscous QCD plasma in the framework of the causal Israel‐Stewart thermodynamics is also obtained. Both the perturbative approach and the numerical solution qualitatively agree in reproducing the viscous corrections to the Hubble parameter, which in the viscous case turns out to be slightly different as compared to the non‐viscous case. Our results are strictly limited within a very narrow temperature‐ or time‐interval in the QCD era, where the quark‐gluon plasma is likely dominant.     

(S_(NN))~(1/2)=130GeV时Au Au碰撞中的反重子与重子比率

按照夸克随机组合的简单组合模型,本文通过分析得出重子反重子比率与夸克反夸克平均产生几率的关系．进一步计算了相对论重离子碰撞过程中各种反粒子与粒子的比率,不需要任何额外假定, 预言的比率与RHIC加速器时Au Au碰撞STAR实验的结果基本一致．表明夸克组合模型能够解释相对论重离子碰撞过程的反粒子与粒子比率．     

The study of gluon energy loss in cold nuclear matter from J/ψ production

The energy loss effects of the incident quark, gluon, and the color octet ccˉ on J/ψ suppression in p-A collisions are studied by means of the experimental data at E866, RHIC, and LHC energy. We extracted the transport coefficient for gluon energy loss from the E866 experimental data in the middle x F region(0.20 x F 0.65) based on the Salgado-Wiedemann(SW) quenching weights and the recent EPPS16 nuclear parton distribution functions together with nCTEQ15. It was determined that the difference between the values of the transport coefficient for light quark, gluon, and heavy quark in cold nuclear matter is very small. The theoretical results modified by the parton energy loss effects are consistent with the experimental data for E866 and RHIC energy, and the gluon energy loss plays a remarkable role on J/ψ suppression in a broad variable range. Because the corrections of the nuclear parton distribution functions in the J/ψ channel are significant at LHC energy level, the nuclear modification due to the parton energy loss is minimal. It is worth noting that we use the color evaporation model(CEM) at leading order to compute the p-p baseline, and the conclusion in this paper is CEM model dependent.     

Calculation of energy density in the colour tube model of relativistic heavy ion collisions

The energy density produced in a relativistic heavy ion collision is calculated within the framework of the colour tube model. The chromoelectric field generated in the collision produces quark-antiquark pairs. The motion of these particles is described by Boltzmann equation. The interaction between the quarks and antiquarks is approximated by introducing a relaxation time.     

Finite size effect on dissociation and diffusion of chiral partners in Nambu-Jona-Lasinio model

The masses of pion and sigma meson modes, along with their dissociation in the quark medium, provide detailed spectral structures of the chiral partners. Collectivity has been observed in pA and pp systems both at LHC and RHIC. In this research, we studied the restoration of chiral symmetry by investigating the finite size effect on the detailed structure of chiral partners in the framework of the Nambu-Jona-Lasinio model. Their diffusion and conduction have been studied using this dissociation mechanism. It is determined that the masses, widths, diffusion coefficients, and conductivities of chiral partners merge at different temperatures in the restoration phase of chiral symmetry. However, merging points are shifted to lower temperatures when finite size effect is introduced into the picture. The strengths of diffusions and conductions are also reduced once the finite size is introduced in the calculations.     

Perturbative vacuum wavefunctional for gauge theories in the Milne space

The spectrum of vacuum fluctuations in the Milne space (i.e. the τ−η$\tau -\eta$ coordinate system) is an important ingredient in the thermalization studies in relativistic heavy ion collisions. In this paper, the Schrödinger functional for the gauge theory perturbative vacuum is derived for the Milne space. The Wigner-transform of the corresponding vacuum density functional is also found together with the propagators. We finally identify the fluctuation spectrum in vacuum, and show the equivalence between the present approach and the symplectic product based method (Dusling et al., 2011; Epelbaum and Gelis, 2013).     

关于QGP中夸克屏蔽位势来自动力论方程的研究

从ＱＧＰ的动力论方程出发，计及运动检验夸克的色电场扰动，采用微扰方法，并在高温极限下得到ＱＧＰ中夸克的分布函数和色电势．给出了考虑运动效应在内的德拜长度λＤ（或屏蔽质量ωＤ）与温度Ｔ的关系，在静态极限下它们与ＱＣＤ理论相符．