One of the main challenges in nuclear physics is the study of the structure of the atomic nucleus. Recently it has been shown that high-energy heavy-ion collisions, such as those at RHIC and the LHC, can serve as a complimentary study to the low-energy experiments. The heavy-ion collisions provide a snapshot of the nuclear distribution at the time of collisions, thus providing a unique,...
Atomic nuclei across the nuclide chart exhibit a wide range of collective degrees of freedom, such as quadruple, triaxial, and octupole deformations. Nuclear deformations enhance the fluctuation of harmonic flow and radial flow, increasing $v_2$, $v_3$, and mean transverse momentum $[p_{\rm T}]$. As demonstrated in recent model studies, the shape parameters can be constrained precisely from...
We argue that diffractive photo-production of jets in coherent nucleus-nucleus ultra-peripheral collisions (UPCs) at high energy is a golden channel to study gluon saturation. By ``coherent'' we mean elastic processes in which both nuclei emerge unbroken after the collision and the final state exhibits large rapidity gaps. We study such processes within the colour glass condensate effective...
Low-energy nuclear experiments well constrain the structure of the nuclear ground state, but whether this picture is consistent at higher energies is an open question. Geometry-driven observables such as the anisotropic flow, $v_{\rm n}$, measured in high-energy heavy-ion collisions access the spatial positions of nucleons on an event-by-event basis and provide a snapshot of the many-body...
We study, to all orders in perturbative QCD, the universal asymptotic behavior of the saturation momentum $Q_s(L)$ controlling the transverse momentum distribution of a fast parton propagating through a dense QCD medium with large size $L$. Due to the double logarithmic nature of the quantum evolution of the saturation momentum, its large $L$ asymptotics is obtained by slightly departing from...
There is increasing interest in using high-energy collisions to study the structure of nuclei, in particular with the high-precision data made possible by collisions performed with pairs of isobaric species.
A systematic study requires a variation of parameters representing nuclear properties such as radius, skin thickness, angular deformation, and short-range correlations, to determine the...
A promising area of development in QCD research is extending beyond the well-studied boost-invariant or (2+1)D picture of QGP evolution and into (3+1)D. Doing so offers a powerful means of further constraining the validity and the parameters of successful collision models and thus allows us to refine our knowledge of the properties of the QGP. However, the extra dimension also introduces...
In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus,...
Measurements of different flow harmonics relative to the participant and spectator planes provide unique insight into the initial conditions and the space-time evolution of the quark-gluon plasma (QGP). Different particle-type dependencies of these flow harmonics allow to separate the effects of QGP evolution and initial state fluctuations. Elliptic flow coefficients ($v_{2}$) relative to the...
Gluons are found to become increasingly dominant constituents of nuclear matter when being probed at higher energies or smaller Bjorken-$x$ values. This has led to the question of the ultimate fate of nuclear gluonic structure and its interaction with external probes at extreme density regimes when approaching the limit allowed by unitarity. In ultraperipheral collisions (UPCs) of relativistic...
We present the first studies of net-charge fluctuations and charge-balance functions using the broad rapidity coverage of the CMS experiment. These types of event-by-event fluctuations are a powerful tool to characterize the thermodynamic properties of the quark-gluon plasma (QGP). The net-charge of the system, e.g., quantified by the $\nu_{dyn}$ observable, is a conserved quantity, meaning...
Photon-induced reactions in ultra-peripheral collisions (UPCs) of heavy nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and collision systems. Beyond the recent ALICE studies of the rapidity and momentum transfer dependence of...
One of the main challenges in the theory of heavy ion collisions is understanding how an initial state of two highly Lorentz-contracted nuclei acquires the features of a hydrodynamic plasma in a characteristic time of 1 fm/c. Arguably, the most successful descriptions of this out-of-equilibrium stage have been established by seeking and finding so-called “attractor” solutions in the various...
Quarkonium measurements in heavy-ion collisions provide insight into the mechanisms which cause the quarkonium bound states to dissociate in the Quark-Gluon Plasma (QGP). The $J/\psi$ suppression and $\Upsilon$ sequential melting provide information on the thermodynamic properties of the QGP, in particular the initial medium temperature. Quarkonium studies in $p$+$p$ and $p$+A collisions serve...
High energy nuclear collisions produce far-from-equilibrium matter with a high density of gluons at early times. We identify for the first time two local order parameters for condensation, which can occur as a consequence of the large density of gluons. We demonstrate that an initial over-occupation of gluons can lead to the formation of a macroscopic zero mode towards low momenta that scales...
FoCal is a high-granularity forward calorimeter to be installed as an ALICE upgrade subsystem during the LHC Long Shutdown 3 and take data during the LHC Run 4. It consists of a compact silicon-tungsten sampling electromagnetic calorimeter (FoCal-E) with pad and pixel longitudinal and transverse segmented readout layers to achieve high spatial resolution for discriminating between isolated...
The Forward Calorimeter (FoCal) in ALICE, which is planned to take data in Run 4, covers a pseudorapidity interval of 3.4 < η < 5.8 for probing non-linear QCD dynamics in an unexplored kinematic region at the LHC.
In its electromagnetic section, layers of high granularity Monolithic Si pixels are alternated to Si pads for sampling the longitudinal development of the electromagnetic showers,...
Long-range azimuthal angle correlations of the produced particles have been observed in high multiplicity proton--lead (p--Pb) and proton--proton (pp) collisions, indicating the presence of collective effects in small systems. The origin of these effects is the subject of intense debate.
In this talk, we present the measurements of $v_{\rm n}$ of charged particle pairs and identified...
Measurements of muon pairs produced via two-photon scattering processes in hadronic (i.e. Non-UPC) Pb+Pb collisions are also presented. These non-UPC measurements provide a novel test of strong-field QED and may be a potentially sensitive electromagnetic probe of the quark-gluon plasma. These measurements include the dependence of the cross-section and angular correlation on the...
How collectivity originates and evolves in the collisions of small-size systems is a highly debated topic in the heavy-ion community. The evolution may be associated with both hydrodynamic and non-hydrodynamic modes. Furthermore, the uncertainties in the description of initial geometry and fluctuations at the sub-nucleonic scale will significantly degrade the predictive power of the available...
In spring 2023, the sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will begin measuring a suite of unique heavy flavor and quarkonia observables with unprecedented statistics and kinematic reach at the RHIC energies using combined electromagnetic and hadronic calorimeters and high precision tracking detectors. A Monolithic Active Pixel Sensor (MAPS)-based vertex detector...
Flow-like signals including the ridge structure observed in large collision systems have also been observed in small collision systems. This leads to questions about the onset of collectivity as well as the parton phase in nuclear collisions. Here [1], we use the string melting version of a multi-phase transport (AMPT) model to study multiparticle cumulants in p+p collisions at 13 TeV. The...
Small systems display large anisotropic flow coefficients that can potentially be interpreted as a hydrodynamic signal. At these moderate multiplicities anisotropic flow is however relatively sensitive to subtle effects. These include the precise experimental procedure, rapidity coverage and gaps as well as effects due to resonance decays. In this talk we quantify these effects for pPb, OO and...
In vacuum, a highly virtual parton fragments into a collimated spray of hadrons—known as a jet. Jets are useful in studying both perturbative and non-perturbative regimes of QCD. In p+p collisions, jet substructure observables are used to study the QCD evolutions and hadronization. In addition, measurements of the event activity dependence of jet properties in p+A collisions can provide new...
Particle production and collective flow of identified hadrons over the $p_{\rm T}$ range from 0 to 6 GeV in high multiplicity events of proton-proton and proton-lead collisions at the Large Hadron Collider (LHC) are investigated by Hydro-Coal-Frag model, which includes hydrodynamic models at low transverse momentum, quark recombination model at intermediate transverse momentum, and string...
Charm and bottom quark production is an important experimental observable that sheds light on the heavy quark interaction with the nuclear medium. With high statistics datasets, tracking and PID at very low transverse momentum, and excellent vertexing capabilities, LHCb performs precision measurements of a rich set of heavy flavor hadrons. These capabilities allow for precise studies of...
Hadronic collisions produce prompt photons which are characterized by a large transverse momentum and absence of event activity in their vicinity. Photons are a robust probe of cold nuclear matter effects in small and large collision systems because they do not interact strongly and are thus insensitive to medium-induced final-state effects. Prompt photon production is dominated by the Compton...
It has been postulated that nonperturbative quantum chromodynamics (QCD) evolution of a single parton in the vacuum can develop long-range collective effects of a multiparton system, reminiscent of those observed in high-energy nuclear interactions from the formation of a quark-gluon plasma. A search for such QCD collective effects is performed by the CMS experiment via two-particle...
The evidence for correlations between particles significantly separated in pseudorapidity in both small and large colliding systems represents one of the most remarkable findings observed at the LHC and at RHIC. Long-range correlations in heavy-ion collisions are considered signatures for the creation of a strongly-coupled quark-gluon plasma, which converts the initial anisotropy of the...
$J/\psi$, a charmonium bound state made of a charm and an anti-charm quark, has been discovered in the 1970s and confirmed the quark model. Because the mass of charms quarks is significantly above the QCD scale, charmonia are considered as excellent probes to test pQCD calculations. Over the past decades, they have been studied extensively at different high-energy colliders. However, their...
Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\Delta\eta$ that are similar to those seen in heavy-ion collisions. The similarity between the $pp$ and heavy-ion measurements raises the possibility that a tiny droplet of the QGP is produced even in $pp$ collisions. However, alternative models that attribute the correlations in...
High-multiplicity measurements in pp and p--Pb collisions have revealed the presence of phenomena typically attributed to the creation of a quark-gluon plasma. Events with multiple parton-parton interactions (MPIs) have been proposed as one possible explanation of this observation. MPIs play a significant role in describing the soft component of the hadronic interactions, and at LHC energies...
With a unique geometry covering the forward rapidity region, the LHCb detector provides unprecedented kinematic coverage from high to very low Bjorken-$x$. The excellent momentum resolution, vertex reconstruction and particle identification allow precision measurements down to very low hadron transverse momentum. This contribution will include recent results on charged and neutral hadron...
Viscous hydrodynamics serves as a successful mesoscopic description of the quark-gluon plasma produced in relativistic heavy-ion collisions. In order to investigate, how such an effective description emerges from the underlying microscopic dynamics we calculate the non-hydrodynamic and hydrodynamic modes of linear response in the sound channel from a first-principle calculation in kinetic...
We train a deep convolutional neural network to predict hydrodynamic results for flow coefficients, average transverse momenta and charged particle multiplicities in ultrarelativistic heavy-ion collisions from the initial energy density profiles [1]. We show that the neural network can be trained accurately enough so that it can reliably predict the hydrodynamic results for the flow...
The study of heavy-flavour particle production as a function of the event activity provides sensitivity to the interplay of hard and soft interaction processes occurring in hadronic collisions, and can shed light into the nucleon underlying partonic structure. Multiple partonic interaction, color-reconnection mechanisms, or modified heavy-quark hadronisation in high-density environments can...
In the view that the short wavelength response can be important in small colliding systems and at early-times of a heavy-ion collision, we investigate the response of the near-equilibrium quark-gluon plasma (QGP) to perturbation at non-hydrodynamic gradients. We propose a conceivable scenario under which sound mode continues to dominate the medium response in this regime. Such a scenario has...
The Color Glass Condensate (CGC) effective theory predicts the earliest stage of relativistic heavy-ion collisions to be a classical state characterized by strong color fields called Glasma. The dynamics of the Glasma are fully determined by the classical Yang-Mills (YM) equations, for which no analytic solution exists. In this talk, we demonstrate how we linearize the YM equations within the...
Recent years have brought interest in the baryon dense region of the QCD phase diagram, probed by low energy heavy ion collisions (HICs) performed by the STAR Beam Energy Scan at RHIC, and by the HADES/CBM experiments at the upcoming FAIR facility. Such HICs are correctly described by hybrid simulations of hadronic transport and viscous hydrodynamics, connected initially by the fluidization of...
Studying the gluon density in nucleons and nuclei require measurements at low-x. The Forward Calorimeter (FoCal) upgrade for ALICE will provide just such measurements. FoCal comprises two components, an Electromagnetic calorimeter (FoCal-E) and a Hadronic Calorimeter (FoCal-H). This poster will present results from the first prototype that informed the design of the second prototype.
In...
Understanding the modification of jets and high-p_T probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different...
QCD multiple scattering plays an essential role in explaining the observed nontrivial phenomena in high energy nuclear collisions. In cold nuclear medium, there are two extensively used theoretical frameworks for describing QCD multiple scatterings, i.e. the high-twist approach and the color glass condensate (gluon saturation) framework that resums multiple eikonal scattering. In this talk, we...
Recently observed signs of collectivity in small systems has highlighted the need for a better understanding of equilibration in small and large collisions systems. In search of this, the QCD effective kinetic theory formulated by Arnold, Moore and Yaffe (AMY) [1] has emerged as a promising candidate. In order to bridge the gap between theory and experiments we introduce ALPACA, a Lorentz...
We developed a formalism to study transverse momentum anisotropies, in particular, the elliptic flow $v_2$, in high-energy hadron-hadron collisions. We derived the impact-parameter dependent cross section up to the next-to-leading order in the eikonal approximation. With this formalism, we take pion-pion collisions for example to interpret the origin and behavior of $v_2$. We calculated $v_2$...
We study the diffusion of heavy quarks in the early stages of high energy nuclear collisions. The background gluon fields are modeled by the standard MV initialization of the glasma, which is then evolved by means of the classical Yang-Mills equations. Heavy quarks are coupled to the evolving glasma fields via relativistic kinetic theory. We compute the momentum broadening as well as the...
In ultra-relativistic heavy-ion collisions, the colliding nuclei are decelerated and kinetic energy is converted into new particles. This energy loss is referred to as baryon stopping. A fundamental question one can ask in the study of high energy heavy-ion collisions is how much baryon stopping there is. This can be quantified by measuring the net proton rapidity distributions. Previous...
The absence of measured high-momentum rescattering (jet quenching) in small collision systems is a long-standing problem in heavy ion physics. Various experimental observables are used to isolate potentially small modifications of high-momentum observables in peripheral lead-lead and proton-lead collisions relative to proton-proton collisions at the LHC. The planned oxygen-oxygen and potential...
Recent studies of event-plane angular correlations with the $\langle \cos\left(a_{1} n_1 \Psi_{n_1}+\cdots+a_{k} n_k \Psi_{n_k}\right) \rangle$ correlators [1] have indicated its weak sensitivity to final state effects in heavy-ion collisions, suggesting that the correlator is a sensitive probe for the initial state of heavy-ion collisions [2]. These investigations suggest that conducting...
The centrality dependence of two-pion Bose-Einstein correlation functions is measured by the PHENIX experiment in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distribution. We extracted the correlation strength parameter $\lambda$, the Lévy index of stability $\alpha$ and...
The ALICE experiment at the Large Hadron Collider (LHC) is designed to investigate the properties of the quark-gluon plasma created in high-energy heavy-ion collisions.
The precise tracking capabilities at low transverse momentum coupled with extensive particle identification over a wide momentum range give the unique opportunity to measure the evolution of the spectral shapes with mass and...
sPHENIX will start data taking in Spring 2023 at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The sPHENIX Event Plane Detector (sEPD) will provide precision measurements of both the event plane and the centrality of heavy-ion collisions recorded during the sPHENIX running. Measurements of the correlation coefficient v2 as a function of transverse momentum carry...
Standard relativistic hydrodynamics, through the years, has been extremely successful in describing the properties of the strongly-interacting matter produced in heavy-ion collision experiments. Recently, there has been a significant theoretical advancement in this field to explain a new phenomenon of spin polarization of hadrons emitted in these processes. Although current models have...
The measurement of fine splitting of observables between ${}^{96}$Ru-${}^{96}$Ru and ${}^{96}$Zr-${}^{96}$Zr collisions at RHIC has opened a new window in probing the deformation of these two isobar isotopes using high-energy nuclear physics. Since these two systems have the same mass, distributed in almost the same size spatial region, the nature of the collective evolution of both systems...
Determined by the nuclear equation of state, the neutron skin of heavy nuclei enables us to connect properties of strong-interaction matter from the nuclear scale ($10^{-15}$ m) to that of neutron stars ($10^3$ m). Of particular interest is the nucleus $^{208}$Pb, owing to its plain structure and experimental availability. Within the hydrodynamic model of heavy-ion collisions, we employ...
Real-time lattice simulations of classical Yang-Mills (CYM) fields are widely used to describe the non-equilibrium evolution of highly occupied and weakly coupled matter of gluons, called glasma, in the early stages of relativistic heavy ion collisions. When we apply it to the study of the glasma, we often assume it to be rapidity-independent, i.e., boost-invariant. This assumption implies a...
The gluon density has been observed to increase rapidly with energy, which would eventually violate unitarity. At high energies, however, nonlinear effects start to become important, slowing down the evolution of the gluon density and hence giving rise to gluon saturation. To study this saturation region of QCD one possibility is to look at diffractive processes, as being approximately...
Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents a series of measurements of dilepton production from photon fusion performed by the ATLAS Collaboration. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. These processes provide...
Centrality dependence of nuclear modification factor of Pi0 in d+Au collision shows a suppression in most central events, which is expected if QGP droplets are formed in small systems, but also a strange enhancement in peripheral collisions. To disentangle possible biases in centrality determination from energy loss , PHENIX presents invariant yields of high pT Pi0 and direct photons as a...
There is substantial current interest in developing solid constraints on the initial-state eccentricity and the final-state viscous attenuation in heavy-ion collisions at RHIC and LHC energies. Such constraints are essential for the precision extraction of the temperature ($T$) and baryon chemical potential ($\mu_B$) dependence of the quark-gluon plasma’s transport coefficients and studies of...
we investigate the existence of far-from equilibrium attractors in momentum moments of the one particle distribution function by means a 3+1D Boltzmann transport approach at fixed η/s with the full collision integral. Attractors are found in the normalized moments of the distribution function and in the evolution of the distribution function itself. We show the results in systems with Bjorken...
In the early stages of heavy-ion collisions, at the highest energies, the system begins in a highly anisotropic state which is far from equilibrium. At later times, the dynamic evolution of the system is well described in the framework of relativistic hydrodynamics which requires local thermodynamic equilibrium. The K\o{}MP\o{}ST framework has had some success in bridging the gap between these...
We investigate the nuclear modification factor $R_{AA}$ and $v_2$, $v_3$, and $v_4$ for high transverse momentum charged particles and $D$ and $B$ mesons for 5 TeV $Pb$+$Pb$ collisions in the LHC [1]. The suppression of high-$p_T$ particles is calculated using DREENA-A dynamical energy loss formalism, while for the event-by-event bulk evolution we utilize three different initializations: 1)...
The collisions of $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr performed at RHIC in 2018, albeit originally intended for the search of the chiral magnetic effect, showed that high-energy heavy-ion collisions could be used as a high-precision tool to probe nuclear structure. One typically models such collision as an initial energy deposition in the vacuum, whose distribution...
Elliptic flow ($v_{2}$) primarily arises from the initial spatial anisotropy of the collision geometry. Elliptic flow of charged hadrons has been observed to differ in magnitude between the isobar collisions, $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr, at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV despite the same nucleon number. This indicates a difference in nuclear structure...
In this work, the origin of anisotropic flow in hybrid approaches, combining viscous relativistic hydrodynamics as well as hadronic transport, is studied.
Anisotropic flow emerges in all stages, albeit being influenced by the shear viscosity in the hydrodynamic phase. Due to the theoretical uncertainties, hybrid approaches use several initial condition models, including SMASH IC, TRENTo and...
Vortex ring formation is a ubiquitous characteristic of strongly-coupled fluids. In asymmetric relativistic heavy-ion collisions, the early-stage longitudinal dynamics can generate toroidal structures of fluid vorticity in the beam direction [1]. In this talk, we will be discussing our systematical study analysis of an experimental observable to examine this structure using state-of-the-art...
The transverse momentum transfer can be measured in exclusive processes. As this momentum transfer is Fourier conjugate to the impact parameter, exclusive processes in Ultra Peripheral Collisions (UPC) at the LHC and at the future EIC will provide access to the spatial distribution of nuclear matter in light and heavy nuclei at high energies.
In this talk we show how non-linear saturation...
The deformation (quadruple, triaxial, octupole, etc.) and substructure (clustering) of atomic nuclei are paramount to developing a complete understanding of nuclear structure. Various cluster structures emerge depending on the excitation energy, the number and kinds of core clusters, and excess neutrons. In low-lying states, clusters are generally tightly bound; however, the correlation...
Collective flow is a notable probe for studying the properties of the medium created in heavy-ion collisions. Directed and elliptic flow, $v_1$ and $v_2$, are sensitive to the dynamics at the early stage of the system evolution and equation of state of the medium. The hadronic interaction cross sections of multi-strange hadrons and φ mesons are expected to be small and their freeze-out...
Transport coefficients, such as viscosity, can be calculated theoretically in weakly coupled quantum field theory, and present interesting information about hydrodynamic models of heavy-ion collisions. We present the results for shear viscosity calculations at leading-log in QCD in a regime of high baryon density, where the chemical potentials are greater than the temperature, which is a very...
It is well established that the late states of a high energy nuclear colli-
sion can be described in terms of relativistic fluid dynamics. An open
problem in this context is how the actual collision and the early time
dynamics directly after it can be described. Phenomenological mod-
els are currently employed here and they have several parameters that
need to be fitted to experimental...
Heavy ion collisions at intermediate and high energies have been in recent years successfully modeled by hybrid approaches. These include viscous hydrodynamic evolution, particlization procedure and hadronic transport. The initial conditions for the hydrodynamic stage can be provided by a wealth of models. In this work we address the initialization from a transport model in the SMASH-vHLLE...
Flow fluctuation in ultra-relativistic heavy-ion collision can be probed by studying the flow decorrelation in transverse momenta or the factorization-breaking coefficients between the harmonic flow in different transverse momentum bins. In particular, by constructing such factorization coefficients between the squares of the flow, the contribution of flow-magnitude and flow-angle...
Exploring the space-time extent of particle production is an important goal of heavy-ion physics, and substantial effort has been made in order to understand the underlying physics behind the experimental observations of non-Gaussian behavior. In experiments, femtoscopic (momentum) correlations are utilized to gain information about the space-time geometry of the particle emitting source....
The photoproduction of $J/\psi$ mesons in ultra-peripheral collisions of heavy ions is a well-known process to study nuclear dynamics at hadron colliders. In particular, the dependence of incoherent $J/\psi$ photoproduction on the Mandelstam variable $|t|$ enables to assess the significance of fluctuations of the spatial distribution, in the impact parameter plane, of the gluon fields within...
In this talk, we present a study of flow and hyperon polarization observables at RHIC BES energies in a MUlti Fluid simulation for Fast IoN collisions (MUFFIN) model. As the acronym suggests, the model is based on multi-fluid approach to relativistic heavy-ion collisions, and treats the initial stage of heavy-ion reaction as mutual inter-penetration of baryon-rich fluids. It is implemented...
The transverse momentum $j_{\rm T}$-dependent jet fragmentation functions have been investigated in p $+$ p and p $+$ Pb collisions at $\sqrt{s_{\rm NN}} = 5.02~{\rm TeV}$ with a multiphase transport model [1] containing both the simple quark coalescence mechanism and a new hybrid hadronization mechanism with coalescence and fragmentation processes [2]. Hadronized by the new hadronization...
We compute the heavy quark momentum diffusion coefficient $\kappa$ using effective kinetic theory at initial stages during the bottom-up isotropization process. We find that the nonequilibrium diffusion coefficient can be approximated with the thermal diffusion coefficient to reasonable accuracy when matching the two for the same energy density. When matching for other quantities (screening...
The rapidity dependent directed flow of particles produced in a relativistic heavy ion collision can be generated in the hydrodynamic expansion of a tilted source. The asymmetry of the pressure leads to a build up of a directed flow of matter with respect to the collision axis. The experimentally observed ordering of the directed flow of baryons, pions and antibaryons can be described as...
The ATLAS experiment has provided data for jet spectra for transverse momentum values up to 1000 GeV and above. At these pT values, it is observed that the nuclear modification factor R_pPb is suppressed for central events and enhanced for peripheral events. One reason for this is that when the jets take a large energy fraction, there is less energy available in the detector regions used to...
Relativistic collision of isobaric systems is found to be valuable in differentiating the nucleon distributions for nuclei with the same mass number. In recent contrast experiment of $^{96}_{44}\text{Ru}+^{96}_{44}\text{Ru}$ versus $^{96}_{40}\text{Zr}+^{96}_{40}\text{Zr}$ collisions at $\sqrt{s_\text{NN}} = 200~\text{GeV}$, the ratios of multiplicity distribution, elliptic flow, triangular...
In the EKRT model for ultrarelativistic heavy-ion collisions, we compute the initial fluctuating QCD-matter energy densities from NLO pQCD and saturation, and describe the subsequent space-time evolution of the system with dissipative fluid dynamics, event by event [1,2,3]. This model agrees remarkably well with the low-$p_T$ flow observables measured in Pb+Pb and Xe+Xe collisions at the LHC,...
In the dipole picture of Deep Inelastic Scattering (DIS) at high energy, the virtual photon fluctuates into a quark-antiquark dipole that interacts with the target color field. This interaction at small-x is naturally described within the Color Glass Condensate (CGC) framework, and one can derive a perturbative Balitsky - Kovchegov (BK) evolution equation that describes the dependence of the...
At the earliest phase of relativistic heavy-ion collisions there is generated a system of gluon fields which can be treated as classical. Numerical simulations show that the system is unstable but a character of the instability is not well understood. We perform a stability analysis of the initial chromoelectric and chromomagnetic which are parallel the beam direction. While a configuration of...
Properties of quark-gluon plasma (QGP) have been studied in high-energy nuclear collisions. Since one needs to describe the dynamical processes of collisions, dynamical and phenomenological models are indispensable to scrutinizing the QGP properties through experimental data. Especially there are a lot of recent works with Bayesian analysis to extract quantitatively, for instance, transport...
The early dynamics in heavy-ion collisions involves a rapid, far from equilibrium evolution. This early pre-equilibrium stage of the dynamics can be modeled using kinetic equations. The effect of this pre-equilibrium stage on final observables derived from transverse momenta of emitted particles is small. The kinetic equations in the relaxation time approximation for a non-boost invariant...
Proton-lead collisions at LHC energies offer unique possibilities to investigate the nuclear modifications of parton distribution functions (PDF) over a wide kinematic range. In this talk, we will present measurements of the dijet per-event yields at center-of-mass energy 8.16 TeV in $p$+Pb collisions. The per-event yields of unfolded dijet pairs will be presented in terms of kinematic...
The study of inclusive jet and dijet production in small (pp and p--Pb) collision systems is essential to probe the initial state of the collision, constrain PDFs, test pQCD predictions and probe cold nuclear matter (CNM) effects. In addition, recent studies at high multiplicity in small collision systems exhibit signatures of collectivity typically associated with the color-deconfined matter...
We study the jet quenching parameter $\hat q$ at the initial pre-equilibrium stages of heavy-ion collisions using the effective kinetic theory description of the anisotropic quark-gluon plasma. This allows us to smoothly close the gap in the literature between the early glasma stage of the collision and the onset of hydrodynamics. We find that the bottom-up evolution of $\hat q$ shows little...
Constraining the properties of the quark--gluon plasma (QGP) depends heavily on our understanding of all phases of heavy-ion collisions. An important advancement has been the definition of symmetric cumulants (SC), which have been shown to be very sensitive to the transport properties of the QGP. Since the SC measurements of lower-order flow harmonics provided more information about the...
We study the hydrodynamization process in the aftermath of ultrarelativistic heavy-ion collisions using effective kinetic theory simulations and different observables. For the pressure ratio $P_T/P_L$, we observe that its late-time evolution becomes universal in units of the kinetic relaxation time for sufficiently large couplings signaling the onset of a hydrodynamical attractor. In contrast,...
We perform a systematic study on the local and global spin polarization
of $\Lambda$ and $\overline{\Lambda}$ hyperons in relativistic heavy-ion collisions at beam energy scan energies via the (3+1)-dimensional CLVisc hydrodynamics model with AMPT and SMASH initial conditions. Following the quantum kinetic theory, we decompose the polarization vector as the parts induced by thermal vorticity,...
Studies of longitudinal de-correlation of anisotropic flow can provide unique constraints on the three-dimensional structure of the initial state and dynamical evolution of the quark-gluon-plasma in heavy-ion collisions. Experimentally, the factorization ratio, $r_{n}(\eta)(n = 2,3)$, is used to quantify the amount of the longitudinal flow de-correlation with pseudorapidity [1-3]. With data...
This talk presents a measurement of longitudinal decorrelation in $pp$ collisions with ATLAS. It is expected that the deposited energy in the transverse $(x,y)$ plane varies, depending on the longitudinal $(z)$ slice examined, which is correlated with the rapidity of the produced particles. Thus, particles from different rapidity slices will have flow vectors that differ in magnitude and...
Double-spin asymmetry in particle and jet productions in longitudinally polarized proton-proton collisions is one of the flagship measurements at RHIC, with the aim of determining the spin fraction of gluons within the proton. Although current next-to-leading order perturbative QCD predictions, based on collinear factorization, have been quite successful in explaining experimental data and...
The enhanced strangeness production in high multiplicity proton-proton (pp) and proton-lead (p--Pb) collisions w.r.t. low multiplicity ones is a well established experimental observation. The origin of the enhancement can be investigated in various ways. One approach is to compare strange particle production in jet vs. underlying event as a function of multiplicity using the jet-like two...
We explore machine learning-based jet and event identification at the future Electron-Ion Collider (EIC) [1]. We study the effectiveness of machine learning-based classifiers at relatively low EIC energies, focusing on (i) identifying the flavor of the jet and (ii) identifying the underlying hard process of the event. We propose applications of our machine learning-based jet identification in...
Heavy quarks are produced in hard partonic scatterings at the very early stage of heavy-ion collisions and they experience the whole evolution of the created Quark-Gluon Plasma medium. Femtoscopic correlations, i.e., two-particle correlations at low relative momentum, are sensitive to the final-state interactions and the extent of the region from which correlated particles are emitted. A study...
This talk presents a new measurement studying the relationship between the production of hard and soft particles through the correlation of Upsilon meson states with the inclusive-charged particle yields in 13 TeV pp collisions. Measurements are made deferentially for Upsilon momentum and for different Upsilon states. The analysis is performed using the full-luminosity ATLAS Run-2 13 TeV pp...
Multiparton interactions in proton-proton collisions have long been a topic of great interest. A new look at them has begun to emerge from work being done to understand the dynamics of ‘small systems’, a topic that is taking center stage in the physics of relativistic heavy-ion interactions. Numerous studies conducted at the LHC and lower energies reveal that proton-proton collisions at high...
Measurements by CMS have provided evidence for the collective behavior of multiparticle production in high-multiplicity proton-proton (pp) and proton-lead (pPb) collisions at the LHC. Although this collectivity aligns with the notion of a hydrodynamic flow origin, it is also possible to interpret it in relation to initial-state correlations caused by, for example, gluon saturation. To...
The PHENIX experiment pioneered measurements of nuclear modification
factor of neutral pions and photons, providing strong evidence
of the formation of Quark-Gluon Plasma (QGP) in Au+Au collisions
at RHIC. In 2014 large amount of 200 GeV Au+Au data were collected,
vastly exceeding the statistics of all similar data taken earlier.
This makes it possible to extend the transverse momentum...
The measurement of neutral mesons in pp and p—Pb collisions allows for testing perturbative QCD calculations, and provides an important baseline for heavy-ion measurements. The combination of the different reconstruction methods in ALICE allows the measurements of neutral mesons in a very wide range of transverse momenta, and thus imposes restrictions on the parton distribution functions and...
The production of light (anti)nuclei in heavy-ion collisions has been extensively studied both experimentally and theoretically for many decades. Two competing models, the statistical hadronisation model (SHM) and the nucleon coalescence model, are commonly used to describe the yields and ratios of light (anti)nuclei to other hadrons in heavy-ion collisions.
Recently, the ALICE...
Measurements of quarkonia production in peripheral and ultra-peripheral heavy-ion collisions are sensitive to photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and to the mechanisms of vector-meson production. In this contribution, recent measurement performed by LHCb will be presented, such as the coherent and incoherent production of $J/\psi$ mesons in...
Using the CGC effective theory together with the hybrid factorisation, we study forward photon+jet production (to be measured in LHCb) in proton-nucleus collisions beyond leading order. We first compute the "real" next-to-leading order (NLO) corrections, i.e. the radiative corrections associated with a three-parton final state, out of which only two are being measured. Then we move to the...
We present the first study of coherent exclusive quarkonium (J/Psi, Upsilon) photoproduction in ultraperipheral nucleus-nucleus collisions (UPCs) at the LHC in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD (pQCD) [1-3]. We make NLO predictions for the J/Psi [1,2] and Upsilon [3] rapidity distributions for lead (Pb) and oxygen (O) beams, and quantify...
A multi-phase transport (AMPT) model has been able to describe a wide range of bulk observables in relativistic heavy ion collisions. However, modern parton distribution functions in nuclei are necessary for studies of pQCD observables such as heavy flavors and high-$p_T$ particles. In this talk, we will first discuss the incorporation of a modern set of parton distribution functions of the...
Photonuclear interactions have been known for decades as a direct probe of the gluon distribution within nuclei and nucleons. However, a long-standing puzzle, that the extracted radii of nuclei appeared much too large, prevented the extraction of precise nuclear geometry information from photonuclear interactions in ultra-peripheral heavy-ion collisions for nearly two decades. Recent...
SHRiMPS is a Monte Carlo model that extends the Khoze–Martin–Ryskin (KMR) model of soft interactions [1] allowing for a complete description from the parton level up to the hadronic final states. This is done with a multichannel eikonal model including two Good-Walker states and the partonic interpretation emerges from seeing the eikonals as tubes of colour flux between the interacting hadrons...
The evolution of jets in the quark gluon plasma can be described in terms of an effective kinetic description. In the small scattering angle limit and neglecting inelastic processes, this gives place to a Boltzmann-diffusion equation ruling the phase space distribution of the jet. In this talk, we will discuss how such a picture generalizes to evolution in non-homogenous media. We will derive...
In the context of relativistic heavy-ion collisions at high beam energies, we investigate the fate of the field perturbations for the second order Israel-Stewart-type hydrodynamics on top of the boost-invariant attractor background. In particular, we analyze both the early-time and late-time asymptotic behavior of these hydrodynamic perturbations at different spatial scales. Our findings...
Hydrodynamic simulations of the quark-gluon plasma (QGP) permit us not only to gauge the transport properties of hot QCD matter from data, but also to constrain the conditions that set the stage for the formation of such matter. Recent measurements from RHIC and LHC demonstrate that the QGP initial condition is impacted by the shape and radial structure of the colliding nuclei. Based on a...
We use QCD kinetic theory to compute photon production in the chemically equilibrating out-of-equilibrium Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We compare the non-equilibrium rates to the production in a thermal QGP and extract the dependence of pre-equilibrium photon production on the kinetic and chemical equilibration time. This allows us to...
Constraining the initial condition of the QGP using experimental observables is one of the most important challenges in our field. Recent studies show that both $\rho_n(v_n, [p_\mathrm{T}])$ (correlation between $v_n$ and event-wise mean $p_\mathrm{T}$) and $[p_\mathrm{T}]$ fluctuations can probe several ingredients of the initial state, such as number and size of sources, volume fluctuation,...
The shape of atomic nuclei is described by a multipole expansion of the parton distribution function. Most nuclies generally have intrinsic deformation, where the quadrupole moment carries the most significant contribution. The shape of a quadrupole deformed nuclies is described by the deformation strength $\beta_2$, and an axial symmetry component $\gamma$. In ultra-relativistic heavy-ion...
Thanks to the injection of noble gases in the LHC beam-pipe while proton or ion beams are circulating, the LHCb spectrometer has the unique capability to function as the highest-energy fixed-target experiment ever built. The resulting beam+gas collisions cover an unexplored energy range that is above previous fixed-target experiments, but below the top RHIC energy for AA collisions. In this...
We aim to probe the early stages of high-energy nuclear collisions using heavy quarks (HQs). The pre-equilibrium stage of relativistic heavy-ion collisions, commonly known as Glasma, evolves according to the classical Yang-Mills (CYM) equations. We study the transverse momentum broadening $\sigma_p$ of HQs in the evolving Glasma using relativistic kinetic theory. We observe that $\sigma_p...
The rapidity dependent directed flow, $v_1(y)$ of identified hadrons as well as the observed $v_1(y)-$splitting between baryon and anti-baryon is very sensitive to the initial three-dimensional distribution of energy and net-baryon density inside the fireball. Therefore, a suitable initial condition that can provide a consistent description of $v_1(y)$ across beam energies could serve as a...
Neutron skin thickness $\Delta r_{\rm np}$ of nuclei and the inferred nuclear symmetry energy are of critical importance to the equation-of-state of dense nuclear matter in neutron stars and heavy-ion collisions. The $\Delta r_{\rm np}$ has traditionally been measured by low-energy hadron-nucleus and nucleus-nucleus scatterings over decades.Recent studies indicate that the neutron skin can...
Isobar collisions performed in RHIC provide a new insight on detecting nuclear deformation in relativistic heavy-ion collisions. Using iEBE-VISHNU hybrid model, we systematically studied the sensativity of nuclear deformation on flow, flow correlation, event-plane correlation and non-linear response between $v_{2}$ and $v_{4}$. A statistical friendly observable with strong sensitivity on...
We study nonequilibrium dynamics of SU(2) lattice gauge theory in Minkowski space-time in a classical-statistical regime, where characteristic gluon occupancies are much larger than unity. In this strongly correlated system far from equilibrium, the correlations of energy and topological densities show self-similar behavior related to a turbulent cascade towards higher momentum scales. I...
Using a current-current correlation function (CF), the photon polarization tensor is calculated for a rotating hot and dense QCD medium. The spectral function (SF) and the dilepton rate (DR) are estimated therefrom. Numerical results show that both SF and DR are enhanced in a rotating medium, especially in a low invariant mass region. SF and DR are also explored in the consequences of the...
The global spin polarization of Lambda hyperon in heavy ion collisions has been well described by spin-vorticity coupling, serving as an evidence for creation of rapid spinning quark-gluon plasma. However the same picture fails to explain the measurement of local spin polarization. Existing kinetic transport theories based on Boltzmann equation cannot describe spin degree of freedoms, calling...
At leading order, the evolution of a particle in the quark gluon plasma will result in the broadening of its transverse momentum. At the level of the particle distribution, this process admits a completely classical description, where the evolution in transverse momentum space can be understood as a diffusive process. However, the full evolution of the parton in the medium is sensitive to...
Suppression of open heavy flavors and quarkonia in heavy-ion collisions is among the most informative probes of the quark-gluon plasma. Interpreting the full wealth of data obtained from the collision events requires a precise understanding of the evolution of heavy quarks and quarkonia as they propagate through the nearly thermal and strongly coupled plasma. Only in the past few years,...
One of the major upgrades to ALICE for LHC Run 4 is the Forward Calorimeter (FoCal). This calorimeter comprises two sections, an Electromagnetic Calorimeter (FoCal-E) and a Hadronic Calorimeter (FoCal-H). Among the physics goals for FoCal is the study of physics at low-x, a regime in which one expects to see signals related to the gluon density in the initial nucleons which form the initial...
Using a semi-classical approach to the kinetic theoretical description of massive spin-1/2 particles in the presence of a magnetic field, we develop a theory of hydrodynamics to describe a relativistic fluid of spin-polarizable and magnetizable particles. We find, for the first time, the relevant transport coefficients of such fluid to exhibit coupling between spin and magnetic field at the...
We extend the classical phase-space distribution function to include the spin and electromagnetic fields coupling and derive the modified constitutive relations for charge current, energy-momentum tensor, and spin tensor. Because of the coupling, the new tensors receive corrections to their perfect fluid counterparts and make the background and spin fluid equations of motion communicate with...
Transport properties of the matter created in heavy-ion collisions, the quark-gluon plasma, contain essential information about quantum chromodynamics (QCD). The Bayesian analysis has shown to be very effective in constraining the QCD matter properties [1], and the combined inclusion of LHC Pb--Pb 5.02 and 2.76 TeV data with additional flow observables has greatly narrowed down the...
The largest uncertainties in modelling of heavy-ion collisions arise from mechanism of energy deposition in initial state. Most models assume colliding ions as transparent objects, during collision of which, spectators fall at large pseudorapidities and have no correlation to final state particle production close to mid-rapidity. On the other hand, in low energy heavy-ion collisions, the...
We explore the effect of the Glasma fields, which are used to describe the very-early stage of heavy-ion collisions, on the dynamics of heavy quarks and jets. We achieve this through numerical simulations of the strong fields, done using classical lattice gauge theory, which are then used as background for the propagation of classical particles. Based on the colored particle-in-cell method, we...
We study the single-inclusive particle production from proton-nucleus collisions in the dilute-dense framework of the color glass condensate (CGC) at next-to-leading order (NLO) accuracy. In this regime, the cross section factorizes into hard impact factors and dipole-target scattering amplitude describing the eikonal interaction of the partons in the target color field. We combine, for the...
We use the Hamiltonian formulation of kinetic theory to perform a stability analysis of nonthermal fixed points in a non-Abelian plasma. We construct a perturbative expansion of the Fokker-Planck collision kernel in an adiabatic approximation and show that the (next-to-)leading order solutions reproduce the known nonthermal fixed point scaling exponents. Working at next-to-leading order, we...
We introduce a systematic characterization of an ensemble of initial density profiles in terms of an average state and an orthonormal basis of statistically uncorrelated modes that represent the event-by-event fluctuations of the initial state. Applying this decomposition to different initial-state models, we quantify the resulting types and probabilities of event-by-event fluctuations and...
The pseudorapidity densities of charged particles and inclusive photons produced in high-energy nuclear collisions are essential observables to characterise the global properties of the collisions, such as the achieved energy density, and to provide important constraints for Monte Carlo model calculations. In the LHC Run 1 and Run 2 configurations, ALICE had large coverage to measure charged...
In heavy ion collisions, the measured spectrum of direct photons at RHIC and the LHC has been found as azimuthally anisotropic as pions. In particular, a large elliptic flow of the direct photos has been observed, which strongly contradicts theoretical predictions, leading to the well-known “direct photon puzzle”. Although it is quite challenging in the conventional hydrodynamical modelings to...
Initial state description in heavy-ion collisions at energies from few to tens of GeV per NN pair brings new challenges as compared to top RHIC or LHC energies. The contraction of the incoming nuclei is much weaker, which results in a long inter-penetration phase and a more complex initial-state geometry. Conventional hydrodynamic models, where the fluid phase starts at a fixed proper time τ0,...
Low-energy nuclear physics study shows that the shape of the nuclear could have a deformation from the spherical symmetry. At high-energy nuclear collisions, whether the picture is still the same is not clear. $^{129}$Xe nucleus has a quadrupole deformation measured by the low-energy nuclear physics experiments. And the Large hadron collider takes a $^{129}$Xe-$^{129}$Xe run at a per-nucleon...
The study of relativistic heavy-ion collisions, such as those of Pb-Pb or Au-Au nuclei performed in the LHC and RHIC, has already demonstrated the capability to produce a deconfined state of hadronic matter called quark-gluon plasma (QGP), which has a collective behavior described by a relativistic viscous hydrodynamic. It is still unknown whether the QGP is also produced in collisions of...
We present a full set of the Boltzmann Equation in Diffusion Approximation (BEDA) for studying thermal equilibration of quarks and gluons. Using BEDA, we first analyse thermalization and quark production of spatially homogeneous systems initially populated by gluons. We observe that soft partons, dominantly produced via medium-induced radiation, rapidly fill a thermal distribution with an...
A central question in heavy-ion collisions is how the initial far-from-equilibrium field-dominated medium evolves and thermalizes. In this work we use the two-particle irreducible (2PI) effective action for the first time with the goal of answering this question. The 2PI effective action is a non-perturbative framework which is derived directly from the underlying quantum-field theory and...
We study the equilibration of a high-momentum parton traveling through a Quark-Gluon Plasma using QCD kinetic theory. We show that the energy and particle number is first transported to the soft sector by collinear cascade and then isotropized by elastic scatterings. For a static thermal background we find that the jet wake can be described by a thermal distribution function with...
The collective behaviours among produced particles are studied via long-range two-particle correlations in many collision systems. In small systems like $pp$ and $p$A collisions, it is essential to estimate the nonflow contribution properly due to the increasing contribution with respect to the large collision systems.
To handle the nonflow in small systems, several methods with different...
In relativistic heavy-ion collisions, the final state collectivity is characterized by the anisotropic flow, measured through flow vector estimations. Hydrodynamics calculations and experimental data show that the flow vector fluctuates as a function of particle transverse momenta event-by-event, indicating fluctuations in the initial energy density of the nuclear collisions. In heavy-ion...
Two-particle transverse momentum correlations enable measurements of the collision dynamics sensitive to momentum currents. Their evolution with collision multiplicity, as proxy of the system lifetime, gives information about the specific shear viscosity, $\eta/s$, and the system relaxation time, $\tau_{\pi}$.
In this talk, measurements of two-particle transverse momentum correlators in pp,...
Measurements of correlations between different symmetry planes in ultrarelativistic heavy-ion collisions probe the initial state and non-linear hydrodynamic response of the medium to initial anisotropies. Earlier studies on symmetry plane correlations (SPC) were conducted by using the Scalar Product method. However, this method is biased by the presence of correlations between different flow...
Angular correlations of identified particles measured in ultrarelativistic proton-proton (pp) and heavy-ion collisions exhibit a number of features which depend on the collision system and particle type under consideration. Those features are produced by mechanisms, such as (mini)jets, elliptic flow, resonance decays, and conservation laws. In addition, of particular importance are those...
Viscous hydrodynamics serves as a successful mesoscopic description of the Quark-Gluon Plasma (QGP) on large time and distance scales. Since highly energetic Jets deposit part of their energy into the QGP in a very localized fashion, it is important to understand to what extent the propagation of the deposited energy can be described within hydrodynamics. We investigate this problem by...
