Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport
Paul Romatschke
备注：
26 pages, 5 figures; v2: reference to Borghini and Gombeaud added who discussed same setup in 2010, typos corrected; v3: minor changes, matches published version
In the limit of short mean free path, relativistic kinetic theory gives rise to hydrodynamics through a systematically improvable gradient expansion. In the present work, a systematically improvable expansion in the opposite limit of large mean free path is considered, describing the dynamics of particles which are almost, but not quite, non-interacting. This non-hydrodynamic "eremitic" expansion does not break down for large gradients, and may be useful in situations where a hydrodynamic treatment is not applicable. As applications, azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions at $\sqrt{s}=5.02$ TeV are calculated from the first order eremitic expansion of kinetic theory in the relaxation time approximation.
Strong multiparticle azimuthal correlations have recently been observed in high energy proton-nucleus collisions. While final state collective effects can be responsible for many of the observations, the domain structure in the classical color field of a high energy nucleus also naturally leads to such correlations. We describe recent calculations of the momentum space 2-particle cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. We find significant differences between Wilson lines from the MV…
The azimuthal anisotropies of the collective transverse flow of hadrons are investigated in a large range of heavy-ion collision energy within the Parton-Hadron-String Dynamics (PHSD) microscopic transport approach which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as dynamical hadronization and hadronic dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ with bombarding energy is successfully described in terms of…
Recent experimental data at the Large Hadron Collider (LHC) confirmed that the soft sector azimuthal anisotropies in central XeXe collisions are sensitive to deformations in the wave function of the Xenon nucleus. Additionally, the CMS experiment found that D meson flow is slightly suppressed compared to other particle species when considering quark number scaling in small systems of pPb compared to PbPb. In this talk we used the D and B Mesons Modular (DAB-MOD) code coupled to Trento+v-USPhydro to calculate the $R_{AA}$ and $v_n$'s of D mesons using different energy loss models and Langevin t…
Azimuthal anisotropies of reconstructed jets [$v_{n}^{jet} (n=2, 3)$] have been investigated in Pb+Pb collisions at the center of mass energy $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV within a framework of a multiphase transport (AMPT) model. The $v_{2}^{jet}$ is in good agreement with the recent ATLAS data. However, the $v_{3}^{jet}$ shows a smaller magnitude than $v_{2}^{jet}$, and approaches zero at a larger transverse momentum. It is attributed to the path-length dependence in which the jet energy loss fraction depends on the azimuthal angles with respect to different orders of event planes. The r…
The azimuthal anisotropies of the collective transverse flow of charged hadrons are investigated in a wide range of heavy-ion collision energies within the microscopic parton-hadron-string dynamics (PHSD) transport approach which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ of charged hadrons with collision ene…
We compute single and double inclusive gluon distributions in classical Yang-Mills simulations of proton-lead collisions and extract the associated transverse momentum dependent Fourier harmonics $v_2(p_T)$ and $v_3(p_T)$. Gluons have a large $v_2$ in the initial state, while odd harmonics such as $v_3$ vanish identically at the initial time $τ=0^{+}$. By the time $τ\lesssim 0.4\,{\rm fm/c}$ final state effects in the classical Yang-Mills evolution generate a non-zero $v_{3}$ and only mildly modify the gluon $v_{2}$. Unlike hydrodynamic flow, these momentum space anisotropies are uncorrelated …
Azimuthal momentum isotropization in the Quark-Gluon Plasma thermalization
University of Heidelberg（海德堡大学）；Shanghai Institute for Advanced Studies, University of Science and Technology of China（上海高等研究院，中国科学技术大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Hefei National Laboratory（合肥国家实验室）；Universidade de Santiago de Compostela（圣地亚哥德孔波斯特拉大学）；Axencia Galega de Innovación (GAIN), Xunta de Galicia（加利西亚自治区创新署（GAIN））
The methods currently used to measure azimuthal distributions of particles in heavy ion collisions assume that all azimuthal correlations between particles result from their correlation with the reaction plane. However, other correlations exist, and it is safe to neglect them only if azimuthal anisotropies are much larger than 1/sqrt(N), with N the total number of particles emitted in the collision. This condition is not satisfied at ultrarelativistic energies. We propose a new method, based on a cumulant expansion of multiparticle azimuthal correlations, which allows to measure much smaller v…
It is commonly believed that azimuthal anisotropies in relativistic heavy ion collisions are generated by hydrodynamic evolution of the strongly interacting quark-gluon plasma. Here we use transport models to study how azimuthal anisotropies depend on the number of collisions that each parton suffers. We find that the majority of $v_2$ comes from the anisotropic escape of partons, not from the parton collective flow, for semi-central Au+Au collisions at 200A GeV. As expected, the fraction of $v_2$ from the anisotropic particle escape is even higher for smaller systems such as d+Au. Our transpo…
Heavy flavor probes provide important information about the in-medium properties of the quark-gluon plasma produced in heavy-ion collisions. In this work, we investigate the effects of 2D+1 event-by-event fluctuating hydrodynamic backgrounds on the nuclear suppression factor and momentum anisotropies of heavy flavor mesons and non-photonic electrons. Using the state-of-the-art D and B mesons modular simulation code (called "DAB-MOD"), we perform a systematic comparison of different transport equations in the same background, including a few energy loss models --- with and without energy loss f…
We show that flow anisotropies in relativistic heavy-ion collisions can be analyzed using a certain technique of shape analysis of excursion sets recently proposed by us for CMBR fluctuations to investigate anisotropic expansion history of the universe. The technique analyzes shapes (sizes) of patches above (below) certain threshold value for transverse energy/particle number (the excursion sets) as a function of the azimuthal angle and rapidity. Modeling flow by imparting extra anisotropic momentum to the momentum distribution of particles from HIJING, we compare the resulting distributions f…
Both hydrodynamics-based models and a multi-phase transport (AMPT) model can reproduce the mass splitting of azimuthal anisotropy ($v_n$) at low transverse momentum ($p_{\perp}$) as observed in heavy ion collisions. In the AMPT model, however, $v_n$ is mainly generated by the parton escape mechanism, not by the hydrodynamic flow. In this study we provide detailed results on the mass splitting of $v_n$ in this transport model, including $v_2$ and $v_3$ of various hadron species in d+Au and Au+Au collisions at the Relativistic Heavy Ion Collider and p+Pb collisions at the Large Hadron Collider. …
Based on the quark coalescence model, we derive relations among the momentum anisotropies of mesons and baryons in relativistic heavy ion collisions from a given, but arbitrary azimuthal distribution for the partons. Besides the familiar even Fourier coefficients such as the elliptic flow, we also pay attention to odd Fourier coefficients such as the directed flow, which has been observed at finite rapidity even at RHIC energies.
Recent experimental results have revealed a surprisingly rich structure of multiparticle azimuthal correlations in high energy proton-nucleus collisions. Final state collective effects can be responsible for many of the observed effects, but it has recently been argued that a part of these correlations are present already in the wavefunctions of the colliding particles. We evaluate the momentum space 2-particle cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. These would correspond to the fl…
We present results for the azimuthal anisotropy of charged hadron distributions in A+A, p+A, d+A, and He3+A collisions within the IP-Glasma+MUSIC model. Obtained anisotropies are due to the fluid dynamic response of the system to the fluctuating initial geometry of the interaction region. While the elliptic and triangular anisotropies in peripheral Pb+Pb collisions at root-s=2.76 TeV are well described by the model, the same quantities in root-s=5.02 TeV p+Pb collisions underestimate the experimental data. This disagreement can be due to neglected initial state correlations or the lack of a de…
We summarize some recent ideas relating to anisotropic particle production in high-energy collisions. Anisotropic gluon distributions lead to anisotropies of the single-particle azimuthal distribution and hence to disconnected contributions to multi-particle cumulants. When these dominate, the four-particle elliptic anisotropy $c_2\{4\}$ changes sign. On the other hand, connected diagrams for $m$-particle cumulants are found to quickly saturate with increasing $m$, a ``coherence'' quite unlike conventional ``non-flow'' contributions such as decays. Finally, we perform a first exploratory pheno…
Azimuthal distributions of radial (transverse) momentum, mean radial momentum, and mean radial velocity of final state particles are suggested for relativistic heavy ion collisions. Using transport model AMPT with string melting, these distributions for Au + Au collisions at 200 GeV are presented and studied. It is demonstrated that the distribution of total radial momentum is more sensitive to the anisotropic expansion, as the anisotropies of final state particles and their associated transverse momentums are both counted in the measure. The mean radial velocity distribution is compared with …
The azimuthal anisotropies of the collective transverse flow of charged hadrons are investigated in a wide range of heavy-ion collision energies within the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which incorporates explicit partonic degrees-of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ of charged hadrons with collision ene…
We argue that energy and momentum deposition from hard partons into quark-gluon plasma induces an important contribution to the final state hadron anisotropies. We also advocate a novel method of Event Shape Sorting which allow to analyse the azimuthal anisotropies of the fireball dynamics in more detail. A use of the method in femtoscopy is demonstrated.
University of Tennessee（田纳西大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；Texas Southern University（德克萨斯南方大学）；Brookhaven National Laboratory（布鲁克海文国家实验室）；University of North Carolina, Greensboro（北卡罗来纳大学格林斯伯勒分校）；University of Houston（休斯顿大学）
We explore parton collisional effects on the conversion of geometry eccentricities into azimuthal anisotropies in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using a multi-phase transport model. The initial eccentricity $\varepsilon_{n}$ (n = 2,3) and flow harmonics $v_{n}$ (n = 2,3) are investigated as a function of the number of parton collisions ($N_{coll}$) during the source evolution of partonic phase. It is found that partonic collisions leads to generate elliptic flow $v_{2}$ and triangular flow $v_{3}$ in Pb+Pb collisions. On the other hand, partonic collisions also result in an evo…
A "breathing'' octupole $^{208}$Pb nucleus: resolving the elliptical-to-triangular azimuthal anisotropy puzzle in ultracentral relativistic heavy ion collisions
We have studied the average charged particle density ($<$dN$_{ch}$/d$η$$>$), transverse momentum ($p_{\mathrm{T}}$) spectra, $<$$p_{\mathrm{T}}$$>$ and azimuthal anisotropies of inclusive charged particles produced in Xe+Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV using A Multiphase Transport Model (AMPT), which includes the deformation of Xe$^{129}$ nucleus. Calculations have been performed with the string melting version of AMPT model and compared with the recent measurements from the ALICE experiment. The model results over predict the measured $<$dN$_{ch}$/d$η$$>$ for central collisions, a…
We review direct photons in the phenomenology of nuclear collisions at relativistic energies. Direct photons carry information about the space-time evolution of nuclear collisions because the QCD medium is transparent against colorless particles. After a status summary of theoretical and experimental studies, transverse momentum spectra and azimuthal momentum anisotropies of direct photons are studied in the context of the hydrodynamic modeling of relativistic nuclear collisions with emphasis on pre-equilibrium photons. It is implied that pre-equilibrium photons can be as important as thermal …
Non-linearities in the harmonic spectra of hadron-nucleus and nucleus-nucleus collisions provide evidence for the dynamical response to azimuthal spatial eccentricities. Here, we demonstrate within the framework of transport theory that even the mildest interaction correction to a picture of free-streaming particle distributions, namely the inclusion of one perturbatively weak interaction ("one-hit dynamics"), will generically give rise to all observed linear and non-linear structures. We further argue that transport theory naturally accounts within the range of its validity for realistic sign…
