In heavy ion collisions, transverse momentum broadening quantifies the modification of a hard probe due to interactions with the quark-gluon plasma (QGP). We calculate momentum broadening in the Glasma, which is the highly non-isotropic precursor stage of the QGP right after the collision. We show that the Glasma leads to anisotropic momentum broadening: high energy partons accumulate more momentum along the beam axis than transverse to it. The physical origin of anisotropic broadening can be traced back to differences in the shapes of chromo-electric and chromo-magnetic flux tubes in the Glasma. We provide semi-analytic results for momentum broadening in the dilute Glasma and numerical results from real-time lattice simulations of the non-perturbative dense Glasma.
In these proceedings, we report on our numerical lattice simulations of partons traversing the boost-invariant, non-perturbative glasma as created at the early stages of collisions at RHIC and LHC. Since these highly energetic partons are produced from hard scatterings during heavy-ion collisions, they are already affected by the first stage of the medium's time evolution, the glasma, which is the pre-equilibrium precursor state of the quark-gluon plasma. We find that partons quickly accumulate transverse momentum up to the saturation momentum during the glasma stage. Moreover, we observe an i…
Jets are important probes of heavy ion collisions as they can provide information on the interaction of a highly energetic parton with the medium it traverses. In the hydrodynamic stage of dense, strongly interacting matter, these interactions can be explained in terms of scattering processes, soft gluon emission and collinear parton splittings. However, jets originate even before the hydrodynamic stage. Here we report on the first numerical simulation of transverse momentum broadening of jets stemming from the interaction of partons with boost-invariantly expanding Glasma flux tubes. The Glas…
The study of jets in heavy-ion collisions provides important information about the interaction of partons with the medium that they traverse. The seeds of jets are highly energetic partons, which are produced from hard scatterings during the collision event. As such, they are affected by all different stages of the medium's time evolution, including the glasma, which is the pre-equilibrium precursor state of the quark-gluon plasma. Here we report on our numerical lattice simulations of partons traversing the boost-invariant, non-perturbative glasma as created at the early stages of collisions …
Gauge invariant momentum broadening of hard probes in glasma
Brandon University（布兰登大学）；Winnipeg Institute for Theoretical Physics（温尼伯理论物理研究所）；University of Toronto（多伦多大学）；National Centre for Nuclear Research（国家核研究中心）
We study the transverse momentum, $p_T$, broadening of charm and beauty quarks in the early stage of high energy nuclear collisions. We aim to compare the diffusion in the evolving Glasma fields with that of a standard, Markovian-Brownian motion in a thermalized medium with the same energy density of the Glasma fields. The Brownian motion is studied via Langevin equations with diffusion coefficients computed within perturbative Quantum Chromodynamics. We find that for small values of the saturation scale, $Q_s$, the average $p_T$ broadening in the two motions is comparable, that suggests that …
We study the evolution of the angular momentum of the heavy quarks in the very early stage of high energy nuclear collisions, in which the background is made of evolving Glasma fields. Given the novelty of the problem, we limit ourselves to the use of toy heavy quarks with a large, unphysical mass, in order to implement the kinetic equations for the angular momentum in the non-relativistic limit. We find that as a consequence of the anisotropy of the background fields, angular momentum fluctuations are also anisotropic: we understand this in simple terms relating the fluctuations of the angula…
We discuss the transverse momentum broadening of hard probes traversing an evolving glasma, which is the earliest phase of the matter produced in relativistic heavy-ion collisions. The coefficient $\hat q$ is calculated using the Fokker-Planck equation, and an expansion in the proper time $τ$ which is applied to describe the temporal evolution of the glasma. The correlators of the chromodynamic fields that determine the Fokker-Planck collision term, which in turn provides $\hat q$, are computed to fifth order in $τ$. The momentum broadening is shown to rapidly grow in time and reach a magnitud…
Heavy quarks, which are produced at the earliest stage of relativistic heavy-ion collisions, probe the entire history of the quark-gluon plasma that is created in the collision. Initially the plasma is populated with chromodynamic fields which can be treated as classical. We study the transport of heavy quarks across such a system, which is called glasma, using a Fokker-Planck equation where the quarks interact with long wavelength chromodynamic fields. We compute field correlators which are used to calculate the collision terms of the transport equation. Finally, the energy loss and momentum …
Anisotropic flow coefficients v_1-v_5 in heavy ion collisions are computed by combining a classical Yang-Mills description of the early time glasma flow with the subsequent relativistic viscous hydrodynamic evolution of matter through the quark-gluon plasma and hadron gas phases. The glasma dynamics, as realized in the IP-Glasma model, takes into account event-by-event geometric fluctuations in nucleon positions and intrinsic sub-nucleon scale color charge fluctuations; the pre-equilibrium flow of matter is then matched to the MUSIC algorithm describing viscous hydrodynamic flow and particle p…
On the Role of Prompt Photons in the Anisotropic Emission of Direct Photons -- Direct Photons from Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV with IP-Glasma Initial Condition
Institute of Particle Physics, Central China Normal University（华中师范大学粒子物理研究所）
A homogeneous color magnetic field is known to be unstable for the fluctuations perpendicular to the field in the color space (the Nielsen-Olesen instability). We argue that these unstable modes, exponentially growing, generate an azimuthal magnetic field with the original field being in the z-direction, which causes the Nielsen-Olesen instability for another type of fluctuations. The growth rate of the latter unstable mode increases with the momentum p_z and can become larger than the former's growth rate which decreases with increasing p_z. These features may explain the interplay between th…
Light-front Hamiltonian jet evolution in the Glasma
University of Jyväskylä（于韦斯屈莱大学）；Helsinki Institute of Physics（赫尔辛基物理研究所）；Instituto Galego de Fisica de Altas Enerxias (IGFAE)（加利西亚高能物理研究所）；Universidade de Santiago de Compostela（圣地亚哥-德孔波斯特拉大学）；School of Physics, Huazhong University of Science and Technology（华中科技大学物理学院）；Axencia Galega de Innovación (GAIN)（加利西亚创新署）
Non-perturbative quark production and transport in the evolving glasma: the WAGASHI event generator
Institute of Physics, Academia Sinica（中央研究院物理研究所）；Physics Program, Graduate School of Advanced Science and Engineering, Hiroshima University（广岛大学先进理工学研究科物理项目）；Kobayashi Maskawa Institute, Nagoya University（名古屋大学小林-益川研究所）；International Institute for Sustainability with Knotted Chiral Meta Matter, Hiroshima University（广岛大学螺旋手性超物质可持续国际研究所）；Hiyoshi Department of Physics and Research and Education Center for Natural Sciences, Keio University（庆应义塾大学日吉理学部及自然科学研究与教育中心）；iTHEMS, TRIP Headquarters, RIKEN（理化学研究所iTHEMS/TRIP总部）
The quark-gluon plasma produced in heavy-ion collisions is anisotropic throughout its evolution. This anisotropy changes the physics of jet-medium interaction, making it dependent on the momentum direction of the jet. In this paper we analyze transverse momentum broadening of a jet parton interacting with soft gluons in an anisotropic plasma. Our analysis equally applies to momentum broadening of quasiparticles in kinetic theory. We subtract contribution from instability modes in the deep infrared and discuss how our calculation should be complemented in that regime. The resulting anisotropic …
In this work we use the IP-Glasma+MUSIC+UrQMD framework to systematically study a wide range of hadronic flow observables at 2.76 TeV. In addition to the single particle spectra and anisotropic flow coefficients $v_n$ previously studied in \cite{1609.02958}, we consider event-plane correlations, non-linear response coefficients $χ_{npq}$, and event shape engineering. Taken together, these observables provide a wealth of insight into the collective behavior of the QGP and initial state fluctuations. They shed light on flow fluctuations, flow at fixed system size but different initial geometries…
The rates governing momentum broadening in a quark-gluon plasma with a momentum anisotropy are calculated to leading-log order for a heavy quark using kinetic theory. It is shown how the problematic singularity for these rates at leading-oder is lifted by next-to-leading order gluon self-energy corrections to give a finite contribution to the leading-log result. The resulting rates are shown to lead to larger momentum broadening along the beam axis than in the transverse plane, which is consistent with recent STAR results. This might indicate that the quark-gluon-plasma at RHIC is not in equil…
We study the diffusion of charm quarks in the early stage of high energy nuclear collisions at the RHIC and the LHC. The main novelty of the present study is the introduction of the color current carried by the heavy quarks that propagate in the evolving Glasma (Ev-Glasma), that is responsible of the energy loss via polarization of the medium. We compute the transverse momentum broadening, $σ_p$, of charm in the pre-thermalization stage, and the impact of the diffusion on the nuclear modification factor in nucleus-nucleus collisions. The net effect of energy loss is marginal in the pre-thermal…
The jet quenching parameter $\hat{q}$ is analyzed for a quark jet propagating in an anisotropic plasma. The momentum anisotropy is calculated at high temperature of the underlying quark-gluon plasma. $\hat{q}$ is explicitly estimated in leading-logarithmic approximation by the broadening of the massless quark interacting via gluon exchange. A plasma instability is present. Strong indications are found that $\hat{q}$ is increasing with increasing anisotropy. Possible implications for the saturation scale $Q_s$ in $A-A$ collisions are pointed out.
Local spin polarization by color-field correlators and momentum anisotropy
Institute of Physics, Academia Sinica（中央研究院物理研究所）；Department of Physics, Duke University（杜克大学物理系）；Physics Division, National Center for Theoretical Sciences（国家理论科学中心物理部）
We calculate the static potential, the drag force and the jet quenching parameter in strongly coupled anisotropic N=4 super Yang-Mills plasma. We find that the jet quenching is in general enhanced in presence of anisotropy compared to the isotropic case and that its value depends strongly on the direction of the moving quark and the direction along which the momentum broadening occurs. The jet quenching is strongly enhanced for a quark moving along the anisotropic direction and momentum broadening happens along the transverse one. The parameter gets lower for a quark moving along the transvers…
In this work, we obtain the leading corrections to the jet momentum broadening distribution in a QCD medium arising from the transverse flow of the matter. We first derive the single-particle propagator of a highly energetic parton resumming its multiple interactions with the homogeneous flowing matter, explicitly keeping the leading subeikonal flow terms. Then, we use this propagator to obtain the jet broadening distribution and its leading moments. We show that this distribution becomes anisotropic in the presence of transverse flow, since its odd moments are generally non-zero and proportio…
We perform numerical simulations of the QCD Boltzmann-Vlasov equation including both hard elastic particle collisions and soft interactions mediated by classical Yang-Mills fields. We provide an estimate of the coupling of jets to a hot plasma which is independent of infrared cutoffs. For weakly-coupled anisotropic plasmas the local rotational symmetry in momentum space is broken. The fields develop unstable modes, forming configurations where B_t>E_t and E_z>B_z. This provides a possible explanation for the experimental observation that high-energy jets traversing the plasma perpendicular to …
We calculate the leading corrections to jet momentum broadening and medium-induced branching that arise from the velocity of the moving medium at first order in opacity. These results advance our knowledge of jet quenching and demonstrate how it couples to collective flow of the quark-gluon plasma in heavy-ion collisions and to the orbital motion of partons in cold nuclear matter in deep inelastic scattering at the electron-ion collider. We also compute the leading corrections to jet momentum broadening due to transverse gradients of temperature and density. We find that these effects lead to …
I use the holographic gauge/gravity duality to systematically calculate the jet quenching parameters in strongly coupled anisotropic plasmas in the presence of external magnetic fields. The magnetic field breaks down spatial rotation symmetry from $SO(3)$ to $SO(2)$, leading to the presence of multiple anisotropic jet quenching parameters, which are evaluated here in two quite different holographic settings. One of them corresponds to a top-down deformation of the strongly coupled $\mathcal{N} = 4$ Super Yang-Mills plasma triggered by an external magnetic field, while the other one is a bottom…
We employ new field-theoretical tools to study photons and jets in a non-equilibrium quark-gluon plasma. Jet broadening and photon emission takes place through radiation which is suppressed by repeated and coherent interaction with the medium. We analyze this physics in an anisotropic plasma such as is created in the early stages of heavy-ion collisions. The anisotropy introduces an angular dependence in radiation and reduces its overall rate. This can affect phenomenological predictions of the rapidity dependence and angular flow of jets and photons.
Photon production from gluon splitting and fusion induced by a magnetic field of arbitrary strength in relativistic heavy-ion collisions
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México（墨西哥国立自治大学核科学研究所）；Instituto de Física, Universidade de São Paulo（圣保罗大学物理研究所）；Instituto de Física Teórica, Universidade Estadual Paulista（圣保罗州立大学理论物理研究所）；Centro de Ciencias Exactas and Departamento de Ciencias Básicas, Facultad de Ciencias, Universidad del Bío-Bío（比奥比奥大学理学院基础科学系精确科学中心）
We calculate leading-order dilepton yields from a quark-gluon plasma which has a time-dependent anisotropy in momentum space. Such anisotropies can arise during the earliest stages of quark-gluon plasma evolution due to the rapid longitudinal expansion of the created matter. Two phenomenological models for the proper time dependence of the parton hard momentum scale, p_hard, and the plasma anisotropy parameter, xi, are constructed which describe the transition of the plasma from its initial non-equilibrium state to an isotropic thermalized state. The first model constructed interpolates betwee…
Anisotropic momentum diffusion coefficients of heavy quarks have been computed in a strongly magnetized quark-gluon plasma beyond the static limit within the framework of Langevin dynamics. Depending on the orientation of the motion of the heavy quark with respect to the direction of the magnetic field, five momentum diffusion coefficients of heavy quark have been estimated in the magnetized thermal medium. Specifically, we have focussed our attention to temperature range and strength of magnetic field satisfying the condition, $\it{i.e.}$ $M\gg\sqrt{eB}\gg T$, $M$ being the mass of heavy quar…
Spectral Signatures of Heavy Quarkonia in a Rotating and Anisotropic Quark-Gluon Plasma: A Holographic Study
College of Mathematics and Physics, China Three Gorges University（三峡大学数学与物理学院）；Center for Astronomy and Space Sciences and Institute of Modern Physics, China Three Gorges University（三峡大学天文与空间科学中心及现代物理研究所）
We present numerical simulations of the SU(2) Boltzmann-Vlasov equation including both hard elastic particle collisions and soft interactions mediated by classical Yang-Mills fields. We provide an estimate of the coupling of jets to a hot isotropic plasma, which is independent of infrared cutoffs. In addition, we investigate jet propagation in anisotropic plasmas, as created in heavy-ion collisions. The broadening of jets is found to be stronger along the beam line than in azimuth due to the creation of field configurations with B_t>E_t and E_z>B_z via plasma instabilities.
