Sergei A. Voloshin, Arthur M. Poskanzer, Raimond Snellings
Recent developments in the field of anisotropic flow in nuclear collision are reviewed. The results from the top AGS energy to the top RHIC energy are discussed with emphasis on techniques, interpretation, and uncertainties in the measurements.
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I review experimental studies of collective phenomena in $\pA$ and A+A collisions presented in the Quark Matter 2014 conference.
These conferences proceedings summarize the experimental findings of collective effects in nuclear collisions, as presented at the Quark Matter 2018 conference.
The observation of long-range collective correlations for particles emitted in high-multiplicity pp and pPb collisions has opened up new opportunities of investigating novel high-density QCD phenomena in small colliding systems. We review experimental results related to the studies of collective phenomena in small systems from RHIC and the LHC over the past several years. Latest development in theoretical interpretations motivated by different frameworks are also reviewed, and confronted with the experimental data. Perspectives on possible future directions are discussed, with the aim of furth…
In these proceedings I review recent developments concerning the hydrodynamic description of the quark-gluon plasma (QGP). I report on the progress towards more realistic simulations and discuss new features about the QGP transport coefficients of the hot (and baryon dense) medium formed in heavy ion collisions. A brief discussion is included on the applicability of hydrodynamics and its extension to the far-from-equilibrium regime.
We celebrate the legacies of our friend and mentor Professor Lianshou Liu who was one of the pioneers for the phenomenology of multi-particle interactions and initiated the physics of relativistic heavy-ion collisions in China. In this article, we discuss some of the recent exciting experimental observations on the collective phenomena including collectivity, chirality, criticality, strangeness production, and thermal equilibrium in high-energy nuclear collisions. Future directions, especially the physics at high baryon density, will be discussed with a focus on the first-order phase boundary …
A microscopic method for calculating nuclear level densities (NLD) is developed, based on the framework of energy density functionals. Intrinsic level densities are computed from single-quasiparticle spectra obtained in a finite-temperature self-consistent mean-field (SCMF) calculation that takes into account nuclear deformation, and is specified by the choice of the energy density functional (EDF) and pairing interaction. The total level density is calculated by convoluting the intrinsic density with the corresponding collective level density, determined by the eigenstates of a five-dimension…
Effects of sequential decay on collective flows and nuclear stopping power in heavy-ion collisions at intermediate energies
本文利用UrQMD模型结合GEMINI++程序研究中等能量金金碰撞，发现逐次衰变显著影响快度分布、集体流和核阻止本领，且考虑该效应后能更好地重现INDRA和FOPI实验数据。
Using transport theory to model central Au + Au collisions in the energy region of 20 - 110 MeV/u, at impact parameters b <= 5 fm, we predict a measurable impact of spinoidal instability as the collective expansion sets in with energy. Two transport models are employed, the pBUU model, solving a Boltzmann-Uehling-Uhlenbeck equation, and the Brownian Motion (BM) model, solving a set of Langevin equations to describe the motion of individual nucleons in a noisy nuclear medium. We find without ambiguity, for the first time, that a combination of delayed equilibration, onset of collective expansio…
Novel transverse-momentum technique is used to analyse charged-particle exclusive data for collective motion in the Ar+KCl reaction at 1.8 GeV/nucl. Previous analysis of this reaction, employing the standard sphericity tensor, revealed no significant effect. In the present analysis, collective effects are observed, and they are substantially stronger than in the Cugnon cascade model, but weaker than in the hydrodynamical model.
The quadrupole collective Hamiltonian, based on relativistic energy density functionals, is extended to include a pairing collective coordinate. In addition to quadrupole shape vibrations and rotations, the model describes pairing vibrations and the coupling between shape and pairing degrees of freedom. The parameters of the collective Hamiltonian are determined by constrained self-consistent relativistic mean-field plus Bardeen-Cooper-Schrieffer (RMF+BCS) calculations in the space of intrinsic shape and pairing deformations. The effect of coupling between shape and pairing degrees of freedom …
In this work we look at the low lying nuclear structure of several N=Z nuclei residing between the doubly magic nucei ^{40} Ca and ^{100} Sn. Using large shell model codes we calculate and discuus the systematics of enegies. We show energy levels, B(E2)'s, static quadrupule moments and g factors. In all cases we compare the results of 2 different interactions which yield significanly different occupation numbers. We compare with the simplest versions of the rotational and vibrational models. By examinnig B(E2)'s and static quadrupole moments we make associations with collective models find tha…
Many features of multiparticle production in ultra-relativistic nuclear collisions reflect the collision geometry and other collision characteristics determining the initial conditions. As the initial conditions affect to a different degree all the particles, it leads to truly multiparticle effects often referred to as anisotropic collective flow. Studying anisotropic flow in nuclear collisions provides unique and invaluable information about the system evolution and the physics of multiparticle production in general. Being not able to cover all aspects of anisotropic flow in one lecture, I de…
We review the recent progress on studying the nuclear collective dynamics by solving the Boltzmann-Uehling-Uhlenbeck (BUU) equation with the lattice Hamiltonian method treating the collision term by the full-ensemble stochastic collision approach. This lattice BUU (LBUU) method has recently been developed and implemented in a GPU parallel computing technique, and achieves a rather stable nuclear ground-state evolution and high accuracy in evaluating the nucleon-nucleon (NN) collision term. This new LBUU method has been applied to investigate the nuclear isoscalar giant monopole resonances and …
The experimental and theoretical studies of Giant Resonances, or more generally of the nuclear collective vibrations, are a well established domain in which sophisticated techniques have been introduced and firm conclusions reached after an effort of several decades. From it, information on the nuclear equation of state can be extracted, albeit not far from usual nuclear densities. In this contribution, which complements other contributions appearing in the current volume, we survey some of the constraints that have been extracted recently concerning the parameters of the nuclear symmetry ener…
A summary of recent researches on nuclear dynamics with realistic microscopic quantum approaches is presented. The Balian-Vénéroni variational principle is used to derive the time-dependent Hartree-Fock (TDHF) equation describing the dynamics at the mean-field level, as well as an extension including small-amplitude quantum fluctuations which is equivalent to the time-dependent random-phase approximation (TDRPA). Such formalisms as well as their practical implementation in the nuclear physics framework with modern three-dimensional codes are discussed. Recent applications to nuclear dynamics, …
Construction of continuous collective energy landscapes for large amplitude nuclear many-body problems
提出构建连续能量面的协议，通过状态重叠约束增强变分原理，以$^{240}$Pu裂变为例验证，可连接任意希尔伯特空间状态。
Collective Enhancement of Nuclear Level Density and its fade-out in $^{161}$Dy
本研究通过中子蒸发谱测量和统计模型分析，揭示了形变核 $^{161}$Dy 中核能级密度的集体增强因子及其随激发能的消退现象，并验证了微观计算结果。
In the last 10 years, we have observed an important increase of interest in the application of time-dependent energy density functional theory (TD-EDF). This approach allows to treat nuclear structure and nuclear reaction from small to large amplitude dynamics in a unified framework. The possibility to perform unrestricted three-dimensional simulations using state of the art effective interactions has opened new perspectives. In the present article, an overview of applications where the predictive power of TD-EDF has been benchmarked is given. A special emphasize is made on processes that are …
We introduce a new relativistic energy density functional constrained by the ground state properties of atomic nuclei along with the isoscalar giant monopole resonance energy and dipole polarizability in $^{208}$Pb. A unified framework of the relativistic Hartree-Bogoliubov model and random phase approximation based on the relativistic density-dependent point coupling interaction is established in order to determine the DD-PCX parameterization by $χ^2$ minimization. This procedure is supplemented with the co-variance analysis in order to estimate statistical uncertainties in the model paramete…
Experimental Evidence of Large Collective Enhancement of Nuclear Level Density and its Significance in Radiative Neutron Capture
本研究通过中子能谱测量发现形变$^{171}$Yb核存在40±3的大核能级密度集体增强因子，结合Oslo数据得到能量依赖的完整图像，对天体物理相关的辐射中子俘获研究有重要意义。
We discuss, in an investigation based on Vlasov equation, the properties of the isovector modes in nuclear matter and atomic nuclei in relation with the symmetry energy. We obtain numerically the dipole response and determine the strength function for various systems, including a chain of Sn isotopes. We consider for the symmetry energy three parametrizations with density providing similar values at saturation but which manifest very different slopes around this point. In this way we can explore how the slope affects the collective response of finite nuclear systems. We focus first on the dipo…
The lattice Hamiltonian method is developed for solving the Vlasov equation with nuclear mean-field based on the Skyrme pseudopotential up to next-to-next-to-next-to leading order. The ground states of nuclei are obtained through varying the total energy with respect to the density distribution of nucleons. Owing to the self-consistent treatment of initial nuclear ground state and the exact energy conservation in the lattice Hamiltonian method, the present framework of solving the Vlasov equation exhibits very stable nuclear ground state evolution. As a first application of the new lattice Ham…
Recent results of the anisotropic flow measurements by the ALICE Collaboration at the LHC are reviewed. Directed, elliptic, triangular, and quadrangular flow are presented differentially vs. transverse momentum, pseudo-rapidity, and the collision centrality for charged and identified particles. Experimental probes of local parity violation using the charge dependent azimuthal correlations with respect to the reaction plane are also discussed.
We present a probable experimental signature of collective enhancement in the nuclear level density (NLD) by measuring the neutron and the giant dipole resonance (GDR) $γ$ rays emitted from the rare earth $^{169}$Tm compound nucleus populated at 26.1 MeV excitation energy. An enhanced yield is observed in both neutron and $γ$ ray spectra corresponding to the same excitation energy in the daughter nuclei. The enhancement could only be reproduced by including a collective enhancement factor in the Fermi gas model of NLD to explain the neutron and GDR spectra simultaneously. The experimental resu…
Comprehensive results on transverse momentum distributions and their ratios for identified light flavor hadrons ($π$, K, p) at low $p_{T}$ and mid-rapidity as a function of charged particle multiplicity are reported for pp collisions at 7 TeV. Particle mass dependent hardening of the spectral shapes in Pb-Pb collisions at 2.76 TeV were attributed to hydrodynamical flow and quantitatively parameterized with Boltzmann-Gibbs Blast Wave fits. In this contribution, we investigate the existence of collective phenomena in small systems: pp, p-Pb and peripheral Pb-Pb where similar patterns are observe…
A review of the main results on the collective type expansion of the compressed and hot fireball formed in heavy ion collisions and some remarks to be considered when comparing multiplicity wise phenomena taking place in A-A, p-A and pp collisions, are followed by a discussion of the experimental results which seem to evidence collective type phenomena in pp collisions at $\sqrt{s}$ = 7 TeV at high charged particle multiplicity. Correlations among the kinetic freeze-out temperature, the average transverse expansion velocity and its profile, as a function of centrality and multiplicity, extract…
A review of the main results of detailed flow analysis in highly central and semi-central heavy ion collisions at SIS energies is presented in the first part of this paper. The influence of the mass of the colliding nuclei and centrality on the collective expansion and the information on the equation of state of compressed and hot baryonic matter is discussed. The second part is dedicated to a similar type of analysis, based on the behaviour of the average transverse momentum as a function of mass of different hadrons, at the other extreme of energy range, where free baryonic fireballs are pro…
For a detailed review of this subject I refer to a recent paper \cite{Voloshin:2008dg}; in this talk I only very briefly comment on a few most important questions: (a) Very recent significant progress in viscous hydrodynamics calculations (b) Initial eccentricity/flow fluctuations, the effect of which has been clarified recently (c) Initial conditions, in particular the role of the gradients in the initial velocity field, (d) Puzzling system size dependence of directed flow (e) Azimuthal correlations that are sensitive to the strong parity violation (f) Future measurements at RHIC and LHC, inc…
Study of Collective Phenomena in Heavy-Ion Collisions Using CMS Open Data
本研究利用CMS公开数据，通过测量$v_0(p_T)$探讨重离子碰撞中集体现象的特征，结果与ATLAS在更高能量下的观测一致。
Complex structural effects in the nuclide production from the projectile fragmentation of 1 A GeV 238U nuclei in a titanium target are reported. The structure seems to be insensitive to the excitation energy induced in the reaction. This is in contrast to the prominent structural features found in nuclear fission and in transfer reactions, which gradually disappear with increasing excitation energy. Using the statistical model of nuclear reactions, relations to structural effects in nuclear binding and in the nuclear level density are demonstrated.
Observation of long-range collective flow in OO and NeNe collisions and implications for nuclear structure studies
本研究利用LHC的CMS探测器，测量OO和NeNe碰撞的长程集体流，发现vₙ系数比值对核结构敏感，相关流体动力学模型可重现实验结果，为核结构与集体动力学的相互作用研究提供新约束。
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