Perturbation solutions of relativistic viscous hydrodynamics for longitudinally expanding fireballs

The solutions of the relativistic viscous hydrodynamics for longitudinally expanding fireballs are investig-ated with the Navier-Stokes theory and Israel-Stewart theory.The energy and the Euler conservation equations for the viscous fluid are derived in Rindler coordinates,by assuming that the longitudinal expansion effect is small.Under the perturbation assumption,an analytical perturbation solution for the Navier-Stokes approximation and numerical solutions for the Israel-Stewart approximation are presented.The temperature evolution with both shear viscous ef-fect and longitudinal acceleration effect in the longitudinal expanding framework are presented.The specific temper-ature profile shows symmetric Gaussian shape in the Rindler coordinates.Further,we compare the results from the Israel-Stewart approximation with the results from the Bjorken and the Navier-Stokes approximations,in the pres-ence of the longitudinal acceleration expansion effect.We found that the Israel-Stewart approximation gives a good description of the early stage evolutions than the Navier-Stokes theory.

Global constraints from RHIC and LHC on transport properties of QCD fluids in CUJET/CIBJET framework

We report results of a comprehensive global х~2 analysis of nuclear collision data from RHIC(0.2 ATeV),LHC1(2.76 ATeV), and recent LHC2(5.02 ATeV) energies using the updated CUJET framework. The framework consistently combines viscous hydrodynamic fields predicted by VISHNU2+1(validated with soft p_T﹤2 GeV bulk observables) and the DGLV theory of jet elastic and inelastic energy loss generalized to QGP fluids with an sQGMP color structure, including effective semi-QGP color electric quark and gluon as well as emergent color magnetic monopole degrees of freedom constrained by lattice QCD data. We vary the two control parameters of the model(the maximum value of the running QCD coupling, c, and the ratio cm of color magnetic to electric screening scales) and calculate the global х~2(α_c,c_m) compared with available jet fragment observables( R_(AA),v_2). A global х~2 minimum is found with α_c≈0.9±0.1 and c_m≈0.25±0.03. Using CIBJET, the event-by-event(ebe) generalization of the CUJET framework, we show that ebe fluctuations in the initial conditions do not significantly alter our conclusions(except for v_3). An important theoretical advantage of the CUJET and CIBJET frameworks is not only its global х~2 consistency with jet fragment observables at RHIC and LHC and with non-perturbative lattice QCD data, but also its internal consistency of the constrained jet transport coefficient, ■(E,T)/T^3, with the near-perfect fluid viscosity to entropy ratio(η/s～T^3/■～0.1-0.2) property of QCD fluids near Tc needed to account for the low p_T﹤2 GeV flow observables. Predictions for future tests at LHC with 5.44 ATeV Xe + Xe and 5.02 ATeV Pb + Pb are also presented.

Mesonic condensation in isospin matter under rotation

We investigate mesonic condensation in isospin matter under rotation.Using the two-flavor NJL effective model in the presence of global rotation,we demonstrate two important effects of rotation on its phase structure:a rotational suppression of the scalar-channel condensates,in particular,the pion condensation region;and a rotational enhancement of the rho condensation region with vector-channel condensate.A new phase diagram for isospin matter under rotation is mapped out on the ω−μI plane where the three distinct phases,corresponding to the σ,π,ρ-dominated regions,respectively,are separated by a second-order line at low isospin chemical potential as well as a first-order line at high rotation and are further connected at a tri-critical point.

A Frequency Determination Method for Digitized NMR Signals

We present a high precision frequency determination method for digitized NMR FID signals.The method employs high precision numerical integration rather than simple summation as in many other techniques.With no independent knowledge of the other parameters of a NMR FID signal(phaseφ,amplitude A,and transverse relaxation time T_(2))this method can determine the signal frequency f_(0)with a precision of 1/(8π^(2)f_(0)^(2)T_(2)^(2))if the observation time T≫T_(2).The method is especially convenient when the detailed shape of the observed FT NMR spectrum is not well defined.When T2 is+∞and the signal becomes pure sinusoidal,the precision of the method is 3/(2π^(2)f_(0)^(2)T_(2))which is one order more precise than the±1 count error induced precision of a typical frequency counter.Analysis of this method shows that the integration reduces the noise by bandwidth narrowing as in a lock-in amplifier,and no extra signal filters are needed.For a pure sinusoidal signal we find from numerical simulations that the noise-induced error in this method reaches the Cramer-Rao Lower Band(CRLB)on frequency determination.For the damped sinusoidal case of most interest,the noise-induced error is found to be within a factor of 2 of CRLB when the measurement time T is 2 or 3 times larger than T2.We discuss possible improvements for the precision of this method.

Probing the color structure of the perfect QCD fluids via soft-hard-event-by-event azimuthal correlations

We develop a comprehensive dynamical framework, CIBJET, to calculate on an event-by-event basis the dependence of correlations between soft （PT 〈2 GeV） and hard （PT 〉 10 GeV） azimuthal flow angle harmonics on the color composition of near-perfect QCD fluids produced in high energy nuclear collisions at RHIC and LHC. CIBJET combines consistently predictions of event-by-event VISHNU2＋I viscous hydrodynamic fluid fields with CUJET3.1 predictions of event-by-event jet quenching. We find that recent correlation data favor a temperature dependent color composition including bleached chromo-electric q（T）＋g（T） components and an emergent chromo-magnetic degrees of freedom re（T） consistent with non-perturbative lattice QCD information in the confinement/deconfinement temperature range.

Issues and Opportunities in Exotic Hadrons

The last few years have been witness to a proliferation of new results concerning heavy exotic hadrons.Experimentally, many new signals have been discovered that could be pointing towards the existence of tetraquarks,pentaquarks, and other exotic configurations of quarks and gluons. Theoretically, advances in lattice field theory techniques place us at the cusp of understanding complex coupled-channel phenomena, modelling grows more sophisticated, and effective field theories are being applied to an ever greater range of situations. It is thus an opportune time to evaluate the status of the field. In the following, a series of high priority experimental and theoretical issues concerning heavy exotic hadrons is presented.

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。

Chiral magnetic effect in isobar collisions from stochastic hydrodynamics

We studied the chiral magnetic effect in AuAu,RuRu,and ZrZr collisions at sNN−√=200GeV.The axial charge evolution was modeled with stochastic hydrodynamics,and geometrical quantities were calculated with the Monte Carlo Glauber model.By adjusting the relaxation time of the magnetic field,we found our results are in good agreement with background subtracted data for AuAu collisions at the same energy.We also made predictions for RuRu and ZrZr collisions.We found a weak centrality dependence on initial chiral imbalance,which implies that the centrality dependence of chiral magnetic effect signals results mainly from the effects of the magnetic field and volume factor.Furthermore,our results show an unexpected dependence on system size.While the AuAu system has larger chiral imbalance and magnetic field,it was observed to have a smaller signal for the chiral magnetic effect due to the larger volume suppression factor.

角动量流体力学

Hydrodynamics is a general theoretical framework for describing the long-time large-distance behaviors of macroscopic physical systems.It has many important applications in various branches of physics,from cosmic expansion and galaxy/star evolutions at the very large scales to relativistic nuclear collisions at the very small scales.The core of hydrodynamics is about physical quantities protected by exact conservation laws,such as energy,momentum and conserved charges.Past hydrodynamic studies almost entirely focus on the energy–momentum conservation and charge conservation.Only very recently,there has been a rapidly increasing interest in understanding the role of angular momentum conservation in the hydrodynamic context and its implications for spin transport of underlying constituents.

Quantifying the chiral magnetic effect from anomalous-viscous fluid dynamics

The Chiral Magnetic Effect（CME） is a macroscopic manifestation of fundamental chiral anomaly in a many-body system of chiral fermions, and emerges as an anomalous transport current in the fluid dynamics framework. Experimental observation of the CME is of great interest and has been reported in Dirac and Weyl semimetals. Significant efforts have also been made to look for the CME in heavy ion collisions. Critically needed for such a search is the theoretical prediction for the CME signal. In this paper we report a first quantitative modeling framework, Anomalous Viscous Fluid Dynamics（AVFD）, which computes the evolution of fermion currents on top of realistic bulk evolution in heavy ion collisions and simultaneously accounts for both anomalous and normal viscous transport effects. AVFD allows a quantitative understanding of the generation and evolution of CME-induced charge separation during the hydrodynamic stage, as well as its dependence on theoretical ingredients. With reasonable estimates of key parameters, the AVFD simulations provide the first phenomenologically successful explanation of the measured signal in 200 AGe V Au Au collisions.