I review the basics and current status of machine learning in particle/nuclear physics, with emphasis on understanding how it works.
The Age of Computation is yet to Come
The theory of classical universal computation was laid down in 1936, was implemented within a decade, became commercial within another decade, and dominated the world’s economy half a century later. This success story relied on the progress in technology. As computers become faster they must become smaller. The history of computer technology has...
The higher-order fluctuations of conserved quantities such as net baryon number are predicted to be sensitive to the non-equilibrium correlation length, $\xi$, and thus serve as indicators of critical behavior. Experimentally, fluctuations of proton and anti-proton numbers have been shown to be reliable proxies for baryons and anti-baryons. In the first Beam Energy Scan (BES-I) at the...
Jets correlated with isolated photons are a promising channel to study jet quenching in heavy-ion collisions, as photons do not interact strongly and therefore constrain the $Q^2$ of the initial hard scattering. The measurement of isolated single photon production constrains NLO pQCD predictions and PDFs, and isolated photon production in Pb-Pb collisions is sensitive to initial geometrical...
Isolated photons and dijets measurements in small collision systems probe the initial state of the collision, providing the opportunity to constrain PDFs, test pQCD predictions, and probe cold nuclear matter effects. In addition, dijet measurements are sensitive to interactions of partons with the medium produced in Pb-Pb collisions that induce modifications in jet properties. Measurements in...
In non-central heavy-ion collisions (HIC), the large initial angular momentum can induce a non-vanishing polarization for hadrons with non-zero spin. The global spin alignment of vector mesons, quantified by the $00^{th}$ element of spin density matrix ($\rho_{00}$), can offer information on the spin-orbital interactions of the QCD medium. Surprisingly large signal of vector meson $\rho_{00}$...
Measurements of high $p_\mathrm{T}$ hadrons produced in hard scattering events offer insight to the modification of jet fragmentation and medium response of the quark-gluon plasma (QGP)
created in ultrarelativistic nucleus-nucleus collisions.
The hard scatter, tagged by an electroweak boson or a jet, fixes initial properties of the showering partons prior to interactions with the QGP. In...
Beams of relativistic heavy ions are accompanied by a large flux of equivalent photons, and thus photon-induced reactions are the dominant interaction mechanism in heavy-ion collisions when the colliding nuclei have transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs) the photon can provide a clean probe of the partonic structure of the nucleus...
Polarization and spin-alignment measurements represent an important tool for the understanding of the particle production mechanisms occurring in proton–proton collisions. When considering heavy-ion collisions, quarkonium polarization could also be used to investigate the characteristics of the hot and dense medium (quark-gluon plasma) created at LHC energies. In ALICE, this observable was...
During the evolution of a heavy ion collision, the system passes close to the O(4) critical point. The order parameter that controls the chiral symmetry is the quark condensate $\langle \bar q q \rangle \sim \phi_a $. Due to the non-zero quark mass, there is a crossover (not a second order phase transition) between the high and low temperature phases. In this talk we will introduce the...
Lattice QCD simulations have shown unequivocally that the transition from hadrons to quarks and gluons is a crossover when the baryon chemical potential is zero or small. Many model calculations predict the existence of a critical point at a value of the chemical potential where current lattice simulations are unreliable. We show how to embed a critical point in a smooth background equation...
The physics interpretation of the recent measurements of the spin polarization of Λ hyperons produced in relativistic heavy-ion collisions is discussed. It is suggested that the polarization measured in the Λ rest frame should be projected along the direction of the total angular momentum that is first transformed to the same frame, and only then averaged over Λ’s with different momenta in the...
Over the last decades, many of the available theoretical jet quenching formalisms have been extended to account for the medium’s finite longitudinal extension and expansion. However, only recently a first-principle approach has been developed that allows to study jet evolution in anisotropic media in the dilute limit. In this talk, we show how to extend some of the previous results to the...
Z bosons can be used to constrain the initial energy, direction, and the flavor of the recoiling parton before its interaction with the quark-gluon plasma. By measuring charged particle yields in Z boson events one can study the in-medium modifications of the recoiling parton showers and as well as the soft particles from medium response. The talk will present measurements of the azimuthal...
Recent observations for the spin polarization and alignments in RHIC and LHC have triggered intensive studies for vorticity-induced polarization and spin dynamics in relativistic fluids. We study the important, yet widely overlooked, role of gluons for spin transport with a connection to local parity violation in quark gluon plasmas. We extend the newly developed quantum kinetic theory for...
In the context of the search for the QCD critical point using
non-Gaussian fluctuations, we obtain the evolution equations for
non-Gaussian cumulants within hydrodynamics to leading order of the
systematic expansion in the magnitude of thermal fluctuations. We
develop diagrammatic technique in which the leading order
contributions are given by tree diagrams. We introduce the concept of
...
We report high-statistics measurements of semi-inclusive distributions of charged jets recoiling from high-$E_{\text{T}}$ direct photon ($\gamma_{\text{dir}}$) and $\pi^{0}$ triggers in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. In a semi-inclusive approach, event bias is induced solely by the choice of trigger; separately utilizing $\gamma_{\text{dir}}$ and $\pi^{0}$...
Angular correlations present in dijet photoproduction are studied, for the first time, using ultraperipheral lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The second moment of the angular distribution, $\langle \cos(2\Phi) \rangle$, where $\Phi$ is the angle between the vector sum $\vec{Q}_\mathrm{T}$ and the vector difference $\vec{P}_\mathrm{T}$ of the...
By including the recently introduced thermal shear term of the spin polarization vector at local equilibrium we determine longitudinal polarization of Λ hyperons emitted from a hot and rotating hadronic medium using the thermal model with single freeze-out. In our analysis we consider top RHIC energy and use the model parameters which were determined in the previous analyses of particle...
Within the framework of a 3+1D Boltzmann transport approach at fixed $\eta/s$ with the full collision integral, we investigate the existence of far-from equilibrium attractors in momentum moments of the one particle distribution function. We first compare our results for a conformal and non conformal gas for different values of $\eta/s$ and $m$, in order to investigate the role of the equation...
We show that the values of the first three cumulants of the baryon number distribution can be used to calculate the isothermal speed of sound and its logarithmic derivative with respect to the baryon number density. We discuss application of this result to heavy-ion collision experiments and address possible challenges, including effects due to baryon number conservation, differences between...
Experimentalists and theorists are pushing towards studying large radius jets in heavy ion collisions in an endeavour to decode signs of induced radiation and medium response with increasing precision. However, even at mid-rapidity, jets are not entirely composed of final state emissions, but contain a varying amount of initial state radiation. This contribution is small for small radius...
Charged particles in heavy-ion collisions have various production mechanisms, such as thermal and associated production, and the importance of each changes with the collision energy. Studying the yields of charged particles provides a way to investigate the properties of the produced QCD matter in heavy-ion collisions and the various production mechanisms. The RHIC Beam Energy Scan (BES)...
In this work, we introduce both gluon and quark degrees of freedom for describing the partonic cascades inside the medium. We present numerical solutions for the set of coupled evolution equations with splitting kernels calculated for the static, exponential and Bjorken expanding media to arrive at medium-modified parton spectra for quark and gluon initiated jets respectively. We discuss novel...
We establish the existence of a far-from-equilibrium attractor in weakly-coupled gauge theory undergoing one-dimensional Bjorken expansion. We demonstrate that the resulting far-from-equilibrium evolution is insensitive to certain features of the initial condition, including both the initial momentum-space anisotropy and initial occupancy. We find that this insensitivity extends beyond the...
The measurements of spin polarization of particles emitted in heavy-ion collisions has opened the possibility for new phenomenological investigations of spin physics in relativistic fluids. The theoretical predictions of global polarization are in agreement with the data, but consistent discrepancies stand out for the local polarization. In this talk, I will show that the covariant theory of...
We explore jet-medium interactions at various scales in high-energy heavy-ion collisions using JETSCAPE 3, a publicly available software framework for Monte Carlo event generators. In jet shower evolution, the virtuality and energy of each jet parton vary considerably. Thus, in high-energy heavy-ion collisions, jets can be used as dynamical probes to investigate the jet-medium interaction at...
The relativistic generalization of the relaxation time approximation proposed by Anderson and Witting [1] is widely used in several fields of physics and, in particular, in the study of the hydrodynamization of the matter produced in ultrarelativistic heavy ion collisions. We demonstrate that the approximation proposed by Anderson and Witting contains basic flaws, not being consistent with...
Even though QGP, when looked at on length scales of order the inverse of its temperature, is best described as a strongly coupled liquid, when it is observed at sufficiently short length scales or probed at sufficiently high exchanged-momentum, asymptotic freedom predicts the presence of quark-like and gluon-like quasi-particles. High energy partons (e.g. those in jet showers) traversing the...
The local Lambda polarization puzzle associated with the model calculations by thermal vorticity has attracted lots of attention in heavy ion community [1].
In addition to the widely studied thermal vorticity effect, we identify an undiscovered contribution from the fluid shear [2]. We obtain the explicit expression for shear-induced polarization (SIP) from quantum kinetic equation and...
Measurements of anisotropic flow in heavy-ion collisions are key to extract properties of the quark-gluon plasma (QGP). The combination of different flow harmonics relative to the participant and spectator planes provides a unique insight into the initial conditions and the space-time evolution of such collisions. In particular, the spectator plane provides novel information about the...
A new approach is presented to explore the singularity structure of lattice QCD in the complex chemical potential and fugacity plane [1, 2, 3]. Our method can be seen as a combination of the Taylor expansion and analytic continuation approaches. Its novelty lies in using rational (Padé) approximants for studying Lee Yang edge singularities, which provide valuable insights to the occur- rence...
Crossover Scenario
If there were a first-order phase transition, some signatures could be expected, but the most challenging is an experimental confirmation of realistic crossover scenario. It is already known from the NS observations / pQCD calculations that a crossover transition to quark matter is likely to occur around 3-5 times normal nuclear density, where a slope parameter on the...
It is well established that hard partons lose energy as they traverse the quark-gluon plasma (QGP). However, while there has been significant work to describe the mechanism by which this occurs, the relative contributions of the microscopic processes have yet to be constrained experimentally. One way to address this question is to exploit the theoretically derived relationship between the...
RHIC's capability to perform relativistic collisions of various ion species provides a unique opportunity to explore and constrain neutron skin thickness and deformation parameters of nuclei.
The study of neutron skin thickness $\Delta r_{np}$ of nuclei can help us directly infer nuclear symmetry energy. Such information is of critical importance to the equation of state of dense...
Fluctuations of conserved charges in a grand canonical ensemble
can be computed on the lattice and, thus, provide theoretical
input for freeze-out phenomenology. Electric charge fluctuations
and the corresponding higher order correlators are extremely
difficult, suffering form the most severe lattice artefacts.
We present new simulation data with a novel discretization where
these...
It has been shown that high-energy partons lose energy when traversing the hot, dense medium produced in heavy-ion collisions. However, the mechanism of the energy loss, including its dependence on the path-length of the shower in the medium and sensitivity to the jet substructure, is not fully understood. This talk presents a new measurement of single jet yields as a function of the azimuthal...
I discuss the recent progress in state-of-the art perturbative QCD calculations of the equation of state at large chemical potential. I describe why these calculations that are reliable at asymptotically high densities constrain the equation of state at neutron star densities, and describe how the theoretical calculations can be confronted with multimessenger observations to empirically...
Jet-medium interactions in the Quark-Gluon Plasma can receive large non-perturbative infrared contributions. These contributions affect transverse jet momentum broadening and jet quenching. Both are influenced by the modified in-medium dispersion of jets encoded in their asymptotic mass.
An IR-safe computation of the latter requires subtracting the unphysical UV limit of electrostatic QCD...
In this talk, we analyze the recent astrophysical constraints in the context of a hadronic equation of state (EoS), in which the baryonic matter is subject to chiral symmetry restoration. We show that it is possible to reconcile the modern constraints on the neutron star (NS) radius and tidal deformability (TD). We find that the softening of the EoS (required by the TD constraint) followed by...
Jet quenching is a well-established signature of quark-gluon plasma formation in heavy ion collisions. Studies of the transverse momentum balance of back-to-back jets, as well as medium-induced modifications to jet shapes and fragmentation functions, provide important experimental constraints on quark-gluon plasma properties. Using a large sample of dijet events from 5.02 TeV PbPb and pp...
The far-from-equilibrium non-abelian plasma is created in the early stage of heavy-ion collision. The “bottom-up” mechanism is the well-studied phenomenological description of its approaching to thermal equilibrium, but has been restricted to leading order coupling within kinetic theory calculation. In our recent work, we provide a next-to-leading-order (NLO) weak-coupling description of the...
We employ an effective kinetic description to study the space-time dynamics and development of transverse flow of small and large collision systems. By combining analytical insights in the few interactions limit with numerical simulations at higher opacity, we are able to describe the development of transverse flow from very small to very large opacities, realised in small and large collision...
The upcoming run of oxygen-oxygen (OO) collisions at the LHC offers unique experimental and theoretical opportunities to address the long standing question of high-momentum rescattering (jet quenching) in small collision systems. We have demonstrated previously that even small energy loss effect can be observed in nuclear modification factor thanks to high precision pQCD baseline calculations...
Given the lack of empirical evidence of weakly interacting dark matter, it is reasonable to look to other candidates such as a confining dark sector with a similar number of particles as the standard model. Twin Higgs mirror matter is one such model that is a twin of the standard model with particles masses 3-6 times heavier than the standard model that solves the hierarchy problem. This...
Dense QCD matter can exhibit spatially modulated regimes. They can be characterized by particles with a moat spectrum, where the minimum of the energy is over a sphere at nonzero momentum. Such a moat regime can either be a precursor for the formation inhomogeneous condensates, or signal a quantum pion liquid. We discuss the underlying physics of the moat regime based on studies in low-energy...
Determining the multi dimensional structure of protons and nuclei at high energy is one central goal of the future Electron-Ion Collider. This fundamental information is a crucial input for models describing the initial state of heavy ion collisions. In particular the event-by-event fluctuating proton geometry should have a strong effect on the flow and multiplicity distribution in high...
While a variety of jet substructure measurements have been performed in heavy-ion collisions, a unified understanding of how the QGP affects the angular and momentum structure of jets remains an open question. One of the prominent puzzles is that measurements indicate no significant modification of the jet mass in heavy-ion collisions relative to proton-proton collisions, but significant...
The strong interaction among stable and unstable hadrons is a fundamental question in nuclear physics and a key ingredient for the description of the equation of state and the understanding of the structure of dense stellar objects such as neutron stars. Traditional measurements, including scattering and hypernuclei experiments, are insufficient to provide stringent constraints to the...
We propose a new model for a homogeneous description of hadron-hadron, hadron-nucleus and nucleus-nucleus collisions, the Gluon Exchange Model (GEM). While technically our model can be regarded as a generalization of the Dual Parton Model by Capella and Tran Thanh Van, it is fundamentally based on the number of exchanged color octets (gluons) and significantly extends the Fock space of states...
In Bayesian analyses of heavy ion collisions up to now one usually uses the TRENTo prescription for the initial state, followed by a free streaming initial stage. In this work, we extend this picture in two ways. Firstly, we generalize the TRENTo formula so that it is able to describe binary scaling. This introduces a parameter which we subsequently use to determine whether binary scaling is...
We outline the role that an early deconfinement phase transition from normal nuclear matter to a color superconducting quark-gluon plasma phase plays for the phenomenology of supernova explosions and binary neutron star mergers. To this end we extend the compact star equation of state (EoS) from vanishing to moderately high temperatures that become accessible in the BM(a)N and MPD experiments...
High energy partons are well established to lose energy when traversing the hot and dense medium produced in heavy-ion collisions. This results in a modification to the transverse momentum distributions of jets, producing a phenomenon known as jet quenching. It has been previously established in Pb+Pb collisions at $\sqrt{s_\textrm{NN}}~=~2.76$~TeV that jet quenching results in significant...
Jet-induced medium response carries the information for the properties of quark gluon plasma produced in high-energy heavy-ion collision. Diffusion wake as an unambiguous part of the medium response will lead to a depletion of soft hadrons in the opposite direction of the jet propagation. New experimental data on Z-hadron correlation in Pb+Pb collisions at the Large Hadron Collider show,...
NA61/SHINE is a fixed target experiment at the CERN Super Proton Synchrotron. The main goals of the experiment are to discover the critical point of strongly interacting matter and to study the properties of the onset of deconfinement. In order to reach these goals, a study of hadron production properties is performed in nucleus-nucleus, proton-proton and proton-nucleus interactions as a...
Using the second law of local thermodynamics and the first-order Palatini formalism, we formulate relativistic spin hydrodynamics for quantum field theories with Dirac fermions, such as QED and QCD, in a torsionful curved background. We work in a regime where spin density, which is assumed to relax much slower than other non-hydrodynamic modes, is treated as an independent degree of freedom in...
The STAR Collaboration has successfully completed the upgrade of the forward detector system located between 2.5 $< \eta <$ 4.0. This upgrade comprises a Forward Calorimeter System, which contains an Electromagnetic Calorimeter and Hadronic Calorimeter; and a Forward Tracking System which consists of a Forward Silicon Tracker and Forward small-strip Thin Gap Chambers. The forward detector...
In this talk we extend the novel expansion scheme introduced in [1] to explore the impact of a strange and electric charge chemical potential. We focus on the equation of state along the strangness neutral line, which allows us to match conditions in heavy ion collision experiments. We are also able to extrapolate different thermodynamic quantities to values of the strangeness and electric...
The LHCb experiment has recently undergone a series of major upgrades: the entire tracking system has been replaced with higher-granularity sensors, the readout electronics have been upgraded, and all hardware triggers have been removed in favor of a new state-of-the-art streaming readout system. In addition, the gaseous target SMOG system has been upgraded with a dedicated storage cell to...
Observations of strong azimuthal anisotropies ($v_n$)-- and their agreement with some hydrodynamic calculations-- in p+A collisions at RHIC and LHC have led to the suggestion that such collisions produce the smallest droplets of QGP. This hypothesis may be tested from a different angle through hyperon polarization measurements. In particular, central p+A collisions may naturally produce an...
Compared to the earlier calculation of the equation of state of QCD with physical light and strange quark masses, performed in 2017, the HotQCD collaboration has accumulated an order of magnitude larger statistics for up to 8th order cumulants on lattices with temporal extent Nt=8 and 12 and added results for Nt=16 that were not available previously. We use these high statistics results on...
The ultra-peripheral collisions (UPC) of relativistic heavy ion beams lead to a diverse set of photon-nucleus interactions.
The measurements of particles and their interaction produced in photo-nuclear reactions can shed light on the QCD dynamics of novel, extremely asymmetric colliding systems, with energies between those available at RHIC and the LHC.
Understanding the hadronic...
Suppression of charmonia is one of the most distinctive signatures of Quark-Gluon Plasma (QGP) in heavy-ion collisions. Suppression can also take place in hadron-nucleus collisions due to cold nuclear matter (CNM) effects where the presence of QGP is not expected. The hadron-nucleus collisions are therefore important as they help to disentangle the effects of the QGP from those due to CNM....
Over the last years, evidence of collective behavior has been observed in high-multiplicity collisions of small systems, however, its origin is not yet understood. In this talk, we will present the first measurement of ultra-long-range azimuthal angle correlations of identified particles in small collision systems by using forward detectors of ALICE, which allows the largest pseudorapidity...
One of the central goals in QCD with non-vanishing conserved charge densities is to find evidence
for the existence of the so-called critical end point (CEP) in the QCD phase diagram. Lattice QCD
calculations at smaller than physical quark masses, combined with our model based understanding of
the QCD phase diagram, suggest that this critical point, if it exists, needs to be searched for...
After 9 years of successful data-taking in proton-proton and heavy ion collisions at a variety of energies, the ATLAS detector started in 2018 the preparations for an ambitious physics project, aiming the exploration of very rare processes and extreme phase spaces, an endeavor that will require a substantial increase in the amount of data to be taken. To accomplish this purpose, a...
In this contribution, the final measurements of the centrality dependence of $R_{\rm AA}$ of non-prompt $\mathrm{D}^0$ and electrons from beauty hadron decays in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented. These measurements provide important constraints to the in-medium mass-dependent energy loss and hadronization of the beauty quark. The integrated non-prompt...
The azimuthal anisotropies observed in small systems can originate from the final state response to the initial geometry as well as from initial momentum anisotropies. Recently it has been proposed that the correlation between the flow coefficient $v_{2}^2$ and the mean $p_\mathrm{T}$ carries information on the origin of flow in small collision systems by showing a characteristic sign change...
We present a novel approach to nonperturbatively estimate the heavy quark momentum diffusion coefficient, which is a key input for the theoretical description of heavy quarkonium production in heavy ion collisions, and is important for the understanding of the elliptic flow and nuclear suppression factor of heavy flavor hadrons. In the heavy quark limit, this coefficient is encoded in the...
The sPHENIX detector at the BNL Relativistic Heavy Ion Collider (RHIC) is currently under construction and on schedule for first data in early 2023. Built around the excellent BaBar superconducting solenoid, the central detector consists of a silicon pixel vertexer adapted from the ALICE ITS design, a silicon strip detector with single event timing resolution, a compact TPC, novel EM...
The jet transport coefficient $\hat{q}$ is the leading coefficient that characterizes the transverse broadening of the hard parton traversing QGP. The transverse kicks received from the medium changes the off-shellness of the hard parton, which leads to enhancement in the gluon emissions. Since the transverse broadening is the dominant mechanism responsible for the suppression of the...
Evidence for the production of top quarks in heavy ion collisions is reported in a data sample of lead-lead collisions recorded in 2018 by the CMS experiment at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV, corresponding to an integrated luminosity of $1.7\pm0.1\,\mathrm{nb}^{-1}$. Top quark pair ($\mathrm{t\bar{t}}$) production is measured in events with...
The experimental observations of anisotropic flows in proton-proton and
proton-nucleus collisions at RHIC and LHC energies has stimulated a big
interest in these small systems as a new study area for the formation and
evolution of the quark-gluon plasma. We investigate the effects of
non-equilibrium dynamics in such systems by comparing a microscopic
nonequilibrium transport approach, the...
The Compressed Baryonic Matter (CBM) experiment is one of the major scientific pillars of the Facility for Antiproton and Ion Research (FAIR), which is expected to become operational in 2025-26. The goal of CBM is to explore the QCD phase diagram in the region of high baryon densities using nucleus-nucleus collisions in the energy range \sqrt{s_{NN}} = 2.9 - 4.9 GeV. CBM will be utilizing peak...
The Multi-Purpose Detector (MPD) is the first experiment at the
NICA Collider, which is in construction at the Joint Institute for
Nuclear Research in Dubna. During initial stage of operation the
complex
will study collisions of heavy ions in for sqrt(s_NN) of 4-11 GeV,
with Bi+Bi collisions at 9.2 GeV, in particular planned for first run.
It is expected that an excited QCD matter with...
In this talk I shall review how the S-matrix formalism can be applied to study the thermal properties of interacting hadrons.
The central idea of this approach is to compute an effective density of state from the scattering phase shifts. As the phase shifts encode a wealth of information about the hadronic interactions, the method can robustly handle many dynamical structures, e.g....
Small collision systems exhibit features that are characteristic of collective flow, a hallmark of QGP formation. However, jet quenching in small systems has not yet been observed, and quantifying or setting limits on the magnitude of jet quenching in small systems is a key element in understanding the limits of QGP formation. In this talk we present a search for jet quenching effects in pp...
We make predictions for rapidity densities of beauty hadrons produced in Pb-Pb collisions at LHC energy. The approach follows that outlined for charm in JHEP 07 (2021) 035, with the canonical suppression as an important ingredient. The hadronic mass spectrum is taken from PDG 2020, with 48 b mesons and 46 b baryons in total. As further input we use the measured cross section for...
Azimuthal angle ($\Delta\phi$) and transverse momentum ($p_\mathrm{T}$) correlations of isolated photons and associated jets, which are sensitive to medium induced parton momentum broadening, are reported for the first time with the latest high statistics pp and PbPb data recorded with the CMS detector at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV. The fully corrected photon+jet azimuthal...
The early production of heavy-flavour partons makes them an excellent probe of the dynamical evolution of QCD systems. Jets tagged by the presence of a heavy-flavour hadron give access to the kinematics of the heavy partons, and along with correlation measurements involving heavy-flavour hadrons allow for comparisons of their production, propagation, and fragmentation across different systems....
We present the measurement of two-particle correlations in hadronic $e^+e^-$ collisions data collected by the Belle detector at KEKB. The clean $e^+e^-$ collision system is conducive for the unambiguous investigation of the azimuthal anisotropy of final-state charged particles found in various heavy ion and proton-proton collisions. Following up on the first examination in $e^+e^-$...
The production mechanism of deuterons, which have a binding energy of 2.2 MeV, is a topic of current interest in high energy heavy-ion collisions, where the system undergoes kinetic freeze-out at temperatures around 100 MeV. Two possible scenarios include (a) statistical thermal process and (b) coalescence of nucleons. Cumulants of deuteron number distributions and proton-deuteron correlations...
Transverse momentum broadening and energy loss of a propagating parton are dictated by the space-time profile of the jet transport coefficient $\hat{q}$ in a dense QCD medium. The spatial gradient of $\hat{q}$ perpendicular to the propagation direction can lead to a drift and asymmetry in parton transverse momentum distribution. Such an asymmetry depends on both the spatial position along the...
Exploring the strong interaction among hadrons, the ALICE Collaboration has for the first time extended the experimental measurements from two- to three-body interactions. These measurements provide unique information on many aspects of strongly-coupled systems, like the genuine three-body interaction, the formation of light nuclei and the search for exotic bound states. Among those, many-body...
The first measurement of $anti-k_{T}$ jets and two-particle angular correlations of charged particles emitted in high energy $e^+e^−$ annihilation is presented. The archived data at a center-of-mass energy of 91-209 GeV were collected with the ALEPH detector at LEP between 1992 and 2000.
At 91 GeV, no significant long-range correlation was observed in either the lab coordinate analysis or...
The jet quenching phenomenon, one of the signatures of the quark-gluon plasma, is well established through experimental measurements at RHIC and LHC. However, the details of the expected dependence of jet-medium interactions on the flavor of the parton initiating the shower are not yet settled. This talk presents the first b jet shapes measurements from 5 TeV PbPb and pp collisions collected...
Quark number susceptibilities as computed in lattice QCD are commonly believed to provide insights into the microscopic structure of QCD matter, in particular its degrees of freedom. We generalize a previously constructed partonic $T$-matrix approach to finite chemical potential to calculate various susceptibilities, in particular for configurations containing a heavy charm quark. At vanishing...
A valuable tool used in the search for QCD's critical point is the computation of cumulants of conserved charge. Near this point, it is expected a sharp increase of this quantity due to divergence of correlation lengths. This calculation requires high statistics, which poses a challenge to hydrodynamics simulations, which tends to be computationally expensive. The issue can be ameliorated by...
The creation of fluid-like quark-gluon plasma in small collision systems has been investigated via elliptical azimuthal anisotropy of emitted particles in these interactions. A novel search for QCD collective effects in hard probes is presented using high-$p_\mathrm{T}$ jets in 13 TeV pp collisions at CMS. Studies of short- and long-range azimuthal correlations inside a jet produced with very...
The suppression of the $J/\psi$ nuclear modification factor has been seen as a trademark signature of final state effects in large collision systems for decades. In small systems, deviations of the nuclear modification from unity had been attributed to cold nuclear matter effects until the observation of strong differential suppression of the $\psi(2S)$ state in $p/d$+A collisions, which...
In this contribution, the similarity between small and large collision systems will be further explored using the underlying event (UE) charged-particle density, $N_{\rm T}$ and the self-normalized version, $R_{\rm T}$. By selecting on $N_{\rm T}/R_{\rm T}$ and topological region, different microscopic processes contributing to the inclusive production can be isolated.
Final measurements of...
Measurements of quarkonia and open-heavy flavor in hadronic collisions provide a unique testing ground for understanding quantum chromodynamics (QCD). Although recently there was significant progress, our understanding of hadronic collisions has been challenged by the observation in high-multiplicity proton-proton (pp) collisions of intriguing effects, such as collective phenomena.
The...
We present a dynamical description of (anti)proton number cumulants and correlation functions in heavy-ion collisions by utilizing hydrodynamics simulations [1]. The cumulants are calculated via an appropriately extended Cooper-Frye procedure describing particlization of an interacting hadron resonance gas [2] while the effects of global baryon number conservation are taken into account using...
Jets have become a prominent tool for studying properties of the quark-gluon plasma through observations of in-medium modifications of parton showers and energy loss patterns in heavy-ion collisions. These effects, termed jet quenching, were expected to depend on the color-charge and/or flavor of the parton initiating the shower. The jet charge observable, defined as the momentum-weighted sum...
The JETSCAPE Collaboration reports a new determination of jet transport coefficients in the
Quark-Gluon Plasma, using both reconstructed jet and hadron data measured at RHIC and the
LHC. The JETSCAPE framework incorporates detailed modeling of the dynamical evolution of
the QGP; a multi-stage theoretical approach to in-medium jet evolution and medium response;
and Bayesian inference for...
The observation of collectivity in small hadronic collisions raises the question whether the tiny droplet of quark gluon plasma can form in systems with size significantly smaller than nucleus-nucleus collisions. Dynamics and hadronization of heavy flavor quarks in small-system collisions provide a powerful tool to address the origin of observed collective phenomena because of their early...
The elliptic flow harmonic $v_{2}\{2k\}$ is determined using Q-cumulants of different orders, with $k=1,...,5$, for 5.02 TeV PbPb collisions. The results were obtained using data from the CMS experiment at the LHC. The $v_{2}\{2k\}$ values show an ordering, with $v_{2}\{2\} > v_{2}\{4\} > \approx v_{2}\{6\} > \approx v_{2}\{8\} > \approx v_{2}\{10\}$. The hydrodynamics behavior of the medium...
In the last few years, several frameworks have achieved the evaluation of the medium-induced gluon radiation spectrum (or rate) with all-order resummation of multiple scatterings for static media. However, conceptual and computational issues arise when embedding approaches including multiple scatterings into dynamic plasmas. In this talk, we will show several paths to overcome these...
The medium modification to particle spectra and the origin of collectivity in small collision systems are widely debated topics in our community.
To address these open questions we propose the study of particle production and collectivity for varying system sizes, presented in decreasing order (Au+Au $>$ Ru+Ru/Zr+Zr $>$ $^{3}$He+Au $>$ d+Au $>$ p+Au $>$ p+p $>$ $\gamma$+Au), available at...
The f$_0$(980) resonance was observed several years ago in $\pi\pi$ scattering experiments. Despite a long history of experimental and theoretical studies, the nature of this short-lived resonance is far from being understood and there is no agreement about its quark structure. According to different models, it has been associated with a meson, considered as a tetraquark, or as a KK molecule....
With current and future heavy-ion experiments focusing on understanding the baryon-rich QCD (Quantum Chromodynamic) matter produced at low collisional energies, first-principle knowledge of the equation of state in such regions is essential for analyzing experimental data in terms of transport simulations and to constrain effective models of QCD.
We construct a novel equation of state (EoS)...
In heavy-ion collisions at relativistic energies, a hot and dense medium called quark-gluon plasma (QGP) is created. Intriguingly, the collective motion of produced particles, which is thought to be a strong evidence of the formation of QGP, is also seen in small systems like pp and p–Pb collisions. Such a study can be done in the ALICE experiment at the LHC via long-range two-particle...
Based on a holographic far-from-equilibrium calculation of the Chiral Magnetic Effect (CME) in an expanding quark-gluon plasma, we study collisions at various energies. We compute the time evolution of the CME current in the presence of a time-dependent axial charge density and subject to a time-dependent magnetic field. The plasma expansion leads to a dilution and eventual annihilation of the...
The large data sample of high-multiplicity pp collisions collected by ALICE allows for the precise measurement of the size of source producing primary hadrons, opening the doors to a study of the interaction of different hadron species using femtoscopy techniques. In this contribution, the momentum correlation between (anti)protons and (anti)deuterons measured in pp collisions at $\sqrt{s} =...
The study of nuclear matter over a wide range of collision energy is provided by the RHIC Beam Energy Scan (BES). One focus of the program, namely to locate the critical point (CP) in the QCD phase diagram, is closely tied to the measurement of kurtosis in net-proton multiplicity distribution as a function of $\sqrt{s_{NN}}$.
Previous results from BES-I obtained with $3.1 \sigma$ significance...
The hydrodynamic modeling of the quark-gluon plasma (QGP) permits us today not only to perform quantitative extractions of the transport properties of the QGP, but also to strongly constrain its initial condition. A growing body of experimental evidence shows that the QGP initial condition is strongly impacted by the shape and radial structure of the colliding nuclei. We discuss the exciting...
The yields of light flavour hadrons and light (anti-)nuclei including (anti-)hypernuclei have been measured by the ALICE collaboration at LHC/CERN at various multiplicity bins in proton-proton, proton-lead and lead-lead collisions. It is observed that the strangeness and (anti-)nuclei production increase non-linearly with charged-particle multiplicity (dNch/dy) and is independent of the...
Recently, STAR reported the isobar (${^{96}_{44}\text{Ru}}+{^{96}_{44}\text{Ru}}$, ${^{96}_{40}\text{Zr}}+{^{96}_{40}\text{Zr}}$) results for chiral magnetic effect (CME) search [1]. The Ru+Ru to Zr+Zr ratio of the CME-sensitive observable $\Delta\gamma$, normalized by elliptic anisotropy ($v_{2}$), is close to the inverse multiplicity ($N$) ratio. In other words, the ratio of the...
The underlying event (UE) has been studied in ALICE for pp collisions at $\sqrt{s}$ =5.02 TeV. The average number density and the average total transverse momentum ($p_{\rm T}$) are studied in the near, away and transverse regions as a function of the leading particle $p_{\rm T}$. Results at 5.02 TeV show qualitatively the same behavior as observed at different energies.
For the first time...
Precision measurements of jet substructure are used as a probe of fundamental QCD processes. The primary Lund jet plane density is a two-dimensional visual representation of the radiation off the primary emitter within the jet that can be used to isolate different regions of the QCD phase space. We present a new measurement with the ALICE detector of the primary Lund plane density for...
We point out that the variance of net-baryon distribution normalized by the Skellam distribution baseline, $\kappa_2[B−B¯]/⟨B+B¯⟩$, is sensitive to the possible modification of (anti)baryon yields due to BB¯ annihilation in the hadronic phase. The corresponding measurements can thus place stringent limits on the magnitude of the BB¯ annihilation and its inverse reaction. We perform Monte Carlo...
It is frequently supposed that quark-gluon plasma created in heavy-ion collisions undergoes free streaming at early times. We examine this issue based on the assumption that a universal attractor dominates the dynamics already at the earliest stages, which offers a way to connect the initial state with the start of the hydrodynamic expansion in an approximate but conceptually transparent...
Deep Learning methods are a popular tool for efficient and fast data analysis in high energy/ nuclear physics experiments. The upcoming Compressed Baryonic Matter (CBM) experiment will study nuclear-nuclear collisions in the range of 10- 40 AGeV at an unprecedented event rate of up to 10MHz, creating about 1TB/s of raw data. In order to run the experiment to its full potential, novel methods...
The search for the chiral magnetic effect (CME) in isobaric collisions of Ru+Ru and Zr+Zr at RHIC was motivated by the assumed similarity of the backgrounds (e.g., $v_n$, $N_{\rm chg}$) for the two isobars. The effects of nuclear structure differences and deformation can lead to essential differences in the backgrounds for the two isobars. Here, we use a quark Glauber model, validated in...
Short-lived resonances can probe strongly interacting matter produced in high-energy heavy ion collisions. K$^{*}(892)^{\pm}$ resonance is particularly interesting because of its very short lifetime (∼ 4 fm/c), comparable to the one of the hadronic phase. Therefore, it may be sensitive to the competing rescattering and regeneration mechanisms which modify the particle’s momentum distributions...
Jets are algorithmic proxies of hard scattered quarks/gluons created in collisions of high energy particles. In the last few years, there has seen an explosion of jet substructure results from all experiments derived from exploiting clustering algorithms. Jet quenching via parton energy loss in heavy ion collisions is an established probe for exploring the properties of the quark-gluon plasma....
The azimuthal anisotropy of parton energy loss in non-central heavy-ion collisions can lead to jet anisotropy which in turn can provide insight into the path-length dependence of jet quenching. Jet anisotropy flow in this study is investigated within the Linear Boltzmann Transport model, in which the dynamical evolution of the QGP is simulated within the CLVisc hydrodynamic model with fully...
Heavy quarkonia are important probes of the matter created in heavy ion-collisions. The complex
heavy-quark potential is an essential ingredient of dynamical models of quarkonium production in
heavy-ion collisions, e.g. in models based on open quantum system approach.
We calculate the complex heavy-quark potential in (2+1)-flavor QCD with physical quark masses on
the lattice using...
Recently, many results suggesting the production of Quark-Gluon Plasma (QGP) in high multiplicity events in small collision systems have been presented. These results were reported with surprise and have been a topic of intense discussion.
The purpose of the analysis presented in this talk is to look for the possibility of QGP formation in small collision systems through the measurement of...
The measurement of neutral mesons in pp collisions allows a test of perturbative QCD calculations and represents an important baseline for heavy-ion studies. Neutral mesons are reconstructed in ALICE with multiple methods in a very wide range of transverse momenta and thus impose restrictions on the parton distribution functions and fragmentation functions over a wide kinematic region....
Anisotropic flow of produced hadrons, in particular of multi-strange hyperons, is an important observable for understanding the dynamics and properties of the QCD matter created in heavy-ion collisions at high net baryon densities. The performance of the Compressed Baryonic Matter (CBM) experiment at FAIR is presented for anisotropic flow measurement relative to the projectile spectator plane...
The ALICE experiment is dedicated to investigating a hot and dense deconfined state of matter created in heavy-ion collisions. Complementary measurements in smaller collision systems have shown signs of collectivity emerging even in simple hadronic collisions. Particle production at the LHC is driven by a complex interplay of soft and hard QCD processes. It is still challenging for modern...
Exclusive vector meson production is a powerful process to probe the small Bjorken-$x$ structure of protons and nuclei, as such processes are especially sensitive to gluonic structure and also provide access to the spatial distribution of small-$x$ gluons in nuclei. A powerful theoretical framework to study vector meson production at high energy, and to describe the initial condition of...
Understanding the phase diagram of QCD by measuring fluctuations of conserved charges in heavy-ion collision is one of the main goals of the beam energy scan program at RHIC. For a precise measurement of the cumulants it is necessary to grasp the role of charge conservation in heavy-ion collision measurements. Within this work, we calculate the role of hadronic interactions and momentum cuts...
The search for experimental signatures of the critical point (CP) of strongly interacting matter is one of the main objectives of the NA61/SHINE experiment at CERN SPS. In the course of the experiment, a beam momentum (13A – 150A GeV/$c$) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb) scan is performed. Local proton density fluctuations in transverse space represent an order parameter...
We tried to locate the initial jet production positions in QGP, using the jet energy loss along the path length direction, the asymmetry perpendicular to the path length from gradient-tomography and the energy momentum distribution inside the jet with deep learning. These machine learning assisted Jet tomography help to locate the jet production positions with reasonable precision that helps...
Hadronic resonances are effective tools for studying the hadronic phase in ultra-relativistic heavy-ion collisions. In fact, their lifetime is comparable to the hadronic phase and resonances are sensitive to the hadronic phase effects such as re-scattering and regeneration processes which might affect the resonance yields and shape of the transverse momentum spectra. $\Lambda(1520)$ has a...
Jet observables, including jet fragmentation transverse momentum $j_{\rm T}$, parallel momentum $p_{\left|\right|}$, jet fragmentation function $\xi$ and jet constituent transverse momentum $p_{\rm T, track}$ distributions, have been investigated in p $+$ p and p $+$ Pb collisions at $\sqrt{s_{\rm NN}} = 5.02~{\rm TeV}$ via a multiphase transport model (AMPT) [1,2] with new hadronization model...
Recent relativistic heavy-ion collision experiments have found evidence for the generation of strong magnetic field and global angular momentum. The numerical simulation of evolution of the QCD medium is based on either magnetohydrodynamics or spin-hydrodynamics for calculation of observables pertaining to magnetic field or global angular momentum, respectively. However, these two effects are...
To probe the Chiral Magnetic Effect (CME) in heavy-ion collisions, a new technique, Sliding Dumbbell Method (SDM) [1] is developed to search for the back-to-back charge separation on event-by-event basis. The SDM helps in selecting the events corresponding to different charge separations ($f_{DbCS}$). The charge separation distributions for each collision centrality is divided into 10...
Event-by-event fluctuations of the mean transverse momentum, $\langle p_{\rm{T} }\rangle$, of charged particles produced in Pb--Pb and Xe--Xe collisions at $\sqrt {s_{\rm{NN} }}= 5.02 $ TeV and $\sqrt {s_{\rm{NN} }}= 5.44$ TeV, respectively, and pp collisions at $\sqrt s = 5.02 $ TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC....
Hydrodynamics is an effective theory for the description of long-wavelength phenomena of fluids, that can be expressed as a small gradient expansion of fluid velocities relative to a thermal background. Thus, hydrodynamics is expected to fail for systems which are far-from-equilibrium. The medium produced in pp collisions at LHC and RHIC energies is an example of such a system. However, recent...
Hydrodynamic expansion and jet quenching are responsible for the production of low and high transverse-momentum ($𝑝_𝑇$) particle in heavy-ion collisions, respectively. However, it is still a challenge to simultaneously describe hadron nuclear modification factor $𝑅_{𝐴𝐴}$ and elliptic flow $𝑣_2$, especially in the intermediate $𝑝_𝑇$ region of 2<$𝑝_𝑇$<10 GeV/c. In this talk, we combine...
Recent measurements reveal that J/ѱ yields increase with increasing charged-particle multiplicity in pp and p—Pb collisions at the LHC. Different mechanisms have been proposed to explain this observation. One of them is the influence of multiple parton interactions (MPI) in the initial state of the collision. Measurements of the excited charmonia, as the ѱ(2S) state, state as a function of...
We present the scale dependence of the jet-medium interactions seen in the modification of jet substructure observables in high-energy heavy-ion collisions by systematic studies with JETSCAPE 3, a publicly available software package of a framework for Monte Carlo event generators [1]. In high-energy heavy-ion collisions, jet partons interact with the quark-gluon plasma medium while changing...
The Compressed Baryonic Matter experiment (CBM) at FAIR aims to investigate the high net baryon density and moderate temperature region of the QCD phase diagram, using collisions of heavy ions at center-of-mass energies of a few GeV per nucleon. Anisotropic transverse flow is among the key observables to study the properties of matter created in such collisions. The CBM performance for charged...
ALICE is the experiment at the LHC specifically designed to study the properties of the quark-gluon plasma (QGP), a deconfined state of matter created in ultrarelativistic heavy-ion collisions. In this context, light-flavour particle production measurements play a key role, as they can probe statistical hadronization and partonic collectivity. Recent measurements in small colliding systems (pp...
In heavy-ion collisions, large transverse momentum partons traverse the colored medium and lose energy via induced gluon radiation and elastic scattering, which modify jet structure relative to jets produced in vacuum. The semi-inclusive recoil jet measurement provides precise, data-driven suppression of the large uncorrelated background and uniquely enables the exploration of medium-induced...
Higher-order cumulants of net-proton distributions are sensitive to the details of the phase structure of the QCD phase diagram. Lattice QCD and QCD-based model calculations indicate that the signs of sixth and eighth-order cumulants have different combinations in the hadronic phase, partonic phase, and near the transition temperature.
In this poster, we report the first measurements of...
Investigation of the femtoscopic correlation functions in heavy ion collisions is an important tool to access the space-time structure of the hadron production of the sQGP. The description of the measured correlation functions is often assumed to be Gaussian or exponential, but a detailed analysis reveals that the statistically correct assumption is a generalized Gaussian, the symmetric...
The evolution of leading partons and jets through deconfined QCD matter is a multi-scale phenomenon and remains as one of the challenging problems in heavy-ion physics. To address this, we use the JETSCAPE framework [1] in which the production of the hard parton is factorized from the evolution of the produced QGP. To incorporate various scales involved in the jet-medium interaction during the...
Previous ALICE publications have shown, in pp collisions at the LHC, an increase of the inclusive J/$\psi$ yields as a function of charged-particle multiplicity. Such an increase was found to be stronger than linear, and both J/$\psi$ and multiplicity were measured at midrapidity. The causes for this behavior have been investigated in previous studies with PYTHIA8 and attributed to possible...
Event-by-event pseudorapidity distributions in heavy-ion collisions are sensitive to longitudinal fluctuations. Their shapes can be decomposed using Legendre polynomials, analogous to the Fourier decomposition for anisotropic flow. A longitudinal decomposition for Xe—Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV and Pb—Pb collisions $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV measured with the...
Anisotropic flow is a key probe of the existence of the quark-gluon plasma. Small collision systems, such as proton-proton (pp) and proton-lead (p--Pb), are usually used to provide the reference data for collisions of heavy nuclei. However, inspection of high-multiplicity p--Pb and pp collisions revealed surprising features, usually attributed to collective effects in heavy-ion...
The precise measurement of the neutral meson production in pp collisions can be used to constrain fragmentation functions and parton density functions needed by pQCD calculations. Additionally, those measurements serve as input for direct photon analyses. Moreover, the dependence of the neutral meson cross section on the event charged-particle multiplicity could give further insight into...
The modification of the substructure of jets due to interactions with a hot QCD medium, the quark-gluon plasma, can be used to study the properties of this medium. Due to the nature of a jet, as a composite object of multiple particles, there are many observables one could construct and study. There is no indication that a single observable will be sufficient to understand the interaction of...
Femtoscopy is a tool that can be used to measure the space-time dimensions of the particle-emitting source created in heavy-ion collisions using two-particle correlations. Additionally to the measurement of the system size, one can extract the average pair-emission asymmetry between two particles with different masses. In this context, the measurement of femtoscopic correlations between...
We postulate that non-perturbative QCD evolution of a single parton in the vacuum will develop the long-range QCD collective effects of a multi-parton system, reminiscent of those observed in high-energy hadronic or nuclear interactions with large final-state particle multiplicity final-state particles [1]. Proton-Proton collisions at the Large Hadron Collider showed surprising signatures of a...
Fluid-dynamical theories are always constructed in terms of an expansion around a given, yet arbitrary, local equilibrium state. This is implemented by the choice of the so-called matching conditions which define the temperature, chemical potential, and velocity of a viscous fluid. Matching conditions are an essential feature of nonequilibrium systems and their consequences to the emergence of...
Heavy-flavor hadrons, containing charm and beauty flavors are believed to be vital probes for the understanding of Quantum Chromodynamics (QCD) in high-energy hadronic collisions: right from the study of production mechanisms in proton-proton ($pp$) collisions to the investigation of Cold Nuclear Matter (CNM) effects in proton-nucleus (p--A) collisions and their suppression in the search of...
State-of-the-art lattice QCD studies of hot and dense strongly interacting matter currently rely on extrapolation from zero or imaginary chemical potentials. The ill-posedness of numerical analytic continuation puts severe limitations on the reliability of such methods. Here we use the more direct sign reweighting method to perform lattice QCD simulation of the QCD chiral transition at finite...
Jets are collimated sprays of hadrons and serve as an experimental tool for studying the dynamics of quarks and gluons. In particular, differential measurements of jet substructure enable a systematic exploration of the parton shower evolution. The SoftDrop grooming technique utilizes the angular ordered Cambridge/Aachen reclustering tree and provides a correspondence between the experimental...
In this talk, I will review the basics of 3+1d quasiparticle anisotropic hydrodynamics (aHydroQP) and highlight some phenomenological comparisons with experimental data at different energies. Then, I will present comparisons of the kaon femtoscopic HBT radii using aHydroQP at 200 GeV where our model shows very good agreement with the experimental data.
Next, I will show predictions of the...
In this poster, measurements of the azimuthal opening angle and transverse momentum correlations between isolated photons and their associated jets, which are sensitive to medium induced parton momentum broadening, are reported for the first time with the high statistics pp and PbPb data recorded in 2017 and 2018. Isolated photon production and their detection techniques will also be summarized.
We explore the transport properties of the QGP matter in the high $\mu_B$ region, where a CEP is incorporated. To this aim we extend the effective dynamical quasi-particle model (DQPM) - constructed for the description of non-perturbative QCD phenomena of the strongly interacting quark-gluon plasma (QGP) - to large baryon chemical potentials, $\mu_B$, including a critical end-point and a 1st...
Collective behaviour of final-state hadrons, and multiparton interactions are studied in high-multiplicity 𝑒𝑝 scattering at a centre-of-mass energy 𝑠√=318 GeV with the ZEUS detector at HERA. Two- and four-particle azimuthal correlations, as well as multiplicity, transverse momentum, and pseudorapidity distributions for charged-particle multiplicities 𝑁ch≥20 are measured. The dependence of...
The very forward energy in hadron-hadron collisions contains information about the fragmentation of the projectile and the target, providing direct insights into the initial stages of high-energy hadronic collisions. By constraining the very forward energy, one can control the event activity in the collision. Results on very forward energy, measured by the ALICE zero degree calorimeters...
The transverse region of di-hadron correlations is known to be
very sensitive to the underlying event (UE), and initial- and
final-state radiation (ISR and FSR). In pp collisions, particle
production in the transverse azimuthal region, with respect to
the leading particle, reaches a plateau for $p^{leading}_{T}>$ 5
GeV/c. In this contribution, a study of the multiplicity...
Transport properties of the matter created in heavy-ion collisions, the quark-gluon plasma (QGP), contain essential information about quantum chromodynamics (QCD). To deepen our understanding of QCD, it is crucial to estimate these transport properties (for instance, specific shear and bulk viscosity) in the light of experimental data as accurately as possible. In this talk, we present our...
There is strong evidence for the formation of small droplets of quark-gluon plasma in $p/d/^{3}$He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) and in $p$+$p$/Pb collisions at the Large Hadron Collider. In particular, the analysis of data at RHIC for different geometries obtained by varying the projectile size and shape has proven insightful. In this talk, we present a new...
We discuss the quantum fluctuations of energy in subsystems of hot relativistic gas for both scalar and spin half particles. For small subsystem sizes, we find a substantial increase of fluctuations compared to those known from standard thermodynamic considerations. However, if the size of the subsystem is sufficiently large, we reproduce the result for energy fluctuations in the canonical...
We study the thermalization of highly energetic partons in a high-temperature QCD plasma. We investigate the non-equilibrium dynamics using an effective kinetic description of QCD, following the evolution of a highly energetic parton from the hard momentum scales all the way to the medium scales, while keeping track of the recoil onto the medium [1-2]. We find that successive radiative...
The Compressed Baryonic Matter experiment (CBM) aims to study the area of the
QCD phase diagram at high net baryon densities and moderate temperatures. It is predicted by Three-fluid Hydrodynamics-based Event Simulator (THESEUS) that one of the signatures of phase transition is a change in shape of the mid-rapidity curvature and yield.
In this contribution we will present CBM performance for...
Properties of dijets may provide sensitive probes of jet quenching in Quark-Gluon Plasma. Dijet invariant mass measurements in small systems provide an essential baseline for such studies in Pb-Pb collisions. In this poster, we present the first measurements of dijet invariant mass in minimum bias pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV by ALICE. Jets are clustered using the...
High statistics data sets from experiments at RHIC and the LHC with small and large collision species have enabled a wealth of new flow measurements, including the event-by-event correlation between observables. One exciting such observable $\rho$($v^2_n$,[$p_T$]) gauges the correlation between the mean transverse momentum ($p_T$) of particles in an event and the various flow coefficients...
Femtoscopic correlations are measured over a broad multiplicity range using data from the LHC Run II collected by the CMS experiment for small colliding systems. Studies are performed for correlations of charged hadrons produced in proton-proton (pp) collisions at $\sqrt{s} = $ 13 TeV and for correlations with all pair combinations of $\text{K}^{0}_{\text{S}}$, $\Lambda$ and...
NA61/SHINE conducts the search for a hypothesized critical point of strongly interacting matter by scanning in collision energy and mass of colliding nuclei. In this field, one of the key methods is to search for the intermittency signal that, if observed, can be related to the effect of the system self-similarity in the vicinity of a possible critical point. This would lead to the power-law...
The magnetic fields generated in non-central heavy-ion collisions are among the strongest fields produced in the Universe, reaching magnitudes comparable to the scale of the strong interactions. Backed by model simulations, the resulting field is expected to be spatially modulated, deviating significantly from the commonly considered uniform profile. In this work, we present the next step to...
Hard partonic scatterings serve as an important probe of quark-gluon-plasma (QGP) properties. The properties of jets and their constituents can provide a tool for understanding the partonic energy loss mechanisms. Low momentum jets offer a unique window into partonic energy loss because they reconstruct the partons which have lost a significant amount of energy to the QGP medium. The main...
Realistic modeling of nucleus-nucleus collisions at finite baryon chemical potential is necessary to extract the location of the critical point on the QCD phase diagram and to understand the findings of the recently concluded Beam Energy Scan (BES) program at RHIC and the future planned experiments at FAIR and NICA. We propose a hydrodynamic model with three new elements. Firstly, we present a...
Quantum chromodynamics (QCD), the fundamental theory of strong interactions, allows the existence of exotic hadrons other than mesons and baryons. An exotic hadron consisting of six quarks is called a dibaryon, and a dibaryon containing strange quarks (multi-strangedibaryon) has not yet been discovered. An exotic hadron consisting of four quarks and an antiquark is called a pentaquark, and the...
The thermodynamical properties of the high-temperature and high-density system produced in relativistic heavy-ion collisions can be understood with a systematic study of the produced hadrons' transverse momentum ($p_{\rm T}$ ) spectra. The $p_{\rm T}$ spectra of these hadrons can be described well by a distribution using the Tsallis statistics. The Tsallis parameters $q$ and $T$ measure the...
The PHENIX experiment measured two-particle Bose- Einstein quantum-statistical correlations of charged kaons in Au+Au collisions $\sqrt{s_{NN}}=200$ GeV collision. The correlation functions are parametrized assuming that the source emitting the particles has a Lévy-shaped characterized by the $\alpha$ Lévy exponent and the $R$ Lévy scale. By introducing the $\lambda$ intercept parameter we...
Recently the PHENIX Collaboration has made available two-particle correlation Fourier coefficients for multiple detector combinations in minimum bias p+p and 0-5% central $p$+Au, $d$+Au, $^3$He+Au collisions at 200 GeV (arXiv:2107.06634). Using these coefficients for three sets of two-particle correlations, azimuthal anisotropy coefficients $v_2$ and $v_3$ are extracted for midrapidity charged...
The different modification of quark- and gluon-initiated jets in the quark-gluon plasma produced in heavy-ion collisions is a long-standing question that has not yet received a definitive answer from experiments. In particular, the relative sizes of the modification of quark and gluon jets differ between theoretical models. Therefore a fully data-driven technique is crucial for an unbiased...
The study of correlation and fluctuation of event-by-event mean transverse momentum ($p_\mathrm{T}$) is a useful tool to understand the dynamics of the system produced in ultrarelativistic heavy-ion collisions. The measurement of higher-order fluctuations of mean-$p_\mathrm{T}$ can help in probing the hydrodynamic behavior of the system and is considered to be a direct way of observing...
One of the main goals of RHIC beam energy scan (BES) program is to search for the signatures of the QCD critical point in heavy-ion collisions. Local density fluctuations near the QCD critical point exhibit strong intermittency which is revealed as the scale (power-law) dependence of scaled factorial moments on phase-space resolution. The scaling exponent is related to the critical component...
Jet fragmentation can be studied using the transverse momentum ($j_T$) and longitudinal momentum fraction ($z$) of constituent particles. The $j_T$ distributions of jet fragments have been measured in pp and p—Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with ALICE, and various parton-shower models reasonably describe the pp results. In this analysis we carry out more detailed measurements of...
Two-particle charge-dependent correlations (balance functions) are sensitive to the production and transport of conserved quantum numbers in the medium created in hadronic collisions. In this con- tribution, recent ALICE measurements of the balance functions of charge, strangeness, and baryon numbers are presented. Balance functions for all combinations of identified charged-hadron ($\pi$, K,...
In non-central heavy-ion collisions, a large orbital angular momentum is created along the direction opposite to the reaction plane, which will be transferred to the spin of quarks through the spin-orbit coupling in parton scatterings. In our recent work, we formulate an improved coalescence model through spin density matrix with phase space dependence, which provides a uniform way to compute...
The measurement of jet deflection in heavy-ion collisions promises to provide unique and incisive insight into the physics of jet quenching and the quasi-particle nature of the QGP. However, observation of large-angle jet deflection favors using low transverse momenta ($p_{\rm T}$) jets, which is challenging in the high-background environment of heavy-ion collisions. The semi-inclusive...
A system of gluon fields generated at the earliest phase of relativistic heavy-ion
collisions can be described in terms of classical fields. Numerical simulations show that the system is unstable but a character of the instability is not well understood. With the intention to systematically study the problem, we analyze a stability of classical chromomagnetic and chromoelectric fields which...
We study the thermodynamic properties, such as the pressure and the entropy density, of a gas of glueballs by considering the contribution of the tower of various glueball states obtained by using recent lattice calculations as well as other model results. We also include, to our knowledge for the first time, the effect of glueball-glueball interaction on thermodynamic properties. The results...
Different than for inclusive jets, leading jet cross sections constitute normalized probability distributions for the leading jet to carry a longitudinal momentum fraction relative to the initial fragmenting parton. The formation and evolution of leading jets can be described by jet functions that satisfy non-linear DGLAP-type evolution equations. We present a parton shower algorithm that...
We employ an effective kinetic theory of Quantum Chromo Dynamics (QCD) to study the pre-equilibrium dynamics of the Quark-Gluon Plasma (QGP) at zero and finite net-baryon density. By investigating the dynamics of the energy-momentum tensor and the conserved charges, we determine the relevant time and temperature scales for the onset of viscous hydrodynamics, and quantify the evolution of the...
Relativistic heavy-ion collisions can study properties of nuclear matter in high-energy experiments like the STAR experiment. Femtoscopy, which relies on information carried by the particles produced in the collisions, is one of methods to learn about the bulk matter. By studying the quantum statistical effects and final state interactions between two particles, one can study spatial and...
Proton-ion collisions at the LHC and RHIC have yielded unexpected trends, notably in measurements of jet nuclear modification factors at different collision centralities. Recent preliminary measurements from STAR in p+Au collisions at $\sqrt{s_{{\rm NN}}}=200$ GeV demonstrate inherent correlations between high-$Q^{2}$ parton scatterings and event activity (EA), measured using either detectors...
In 2018, STAR installed the Event Plane Detector (EPD) with a pseudorapidity coverage of $2.15<|\eta|<5.09$. The EPD has enhanced STAR's capabilities in triggering, centrality measurement and event plane determination. Due to its fine radial granularity, it can also be utilized to measure pseudorapidity distributions of charged particles. In order to make such a measurement, the response of...
Hadronic resonances are interesting probes of the hot and dense matter created in the heavy-ion collision. Due to their short lifetimes, resonances are useful tools to understand the mechanism of particle production and properties of the hadronic phase created after the collision. The yield of resonances might be modified with respect to expectations due to effects such as rescattering and...
The quark model has proven successful in describing the basic building blocks of strongly interacting particles in the Standard Model, where hadronic states consist of quarks and gluons. At the same time, Lattice QCD predicts the possibility of glueball candidates in the mass range 1550-1750 MeV/$c^{2}$, which have never been observed.
The experimental search for the existence of mesons...
We derive Boltzmann equations for massive spin-1/2 fermions with local and nonlocal collision terms from the Kadanoff--Baym equation in the Schwinger--Keldysh formalism, properly accounting for the spin degrees of freedom. The Boltzmann equations are expressed in terms of matrix-valued spin distribution functions, which are the building blocks for the quasi-classical parts of the Wigner...
The main goal of the ALICE experiment is to study the physics of strongly interacting matter, including the properties of the Quark-Gluon Plasma (QGP). The relative production of strange hadrons with respect to non-strange hadrons in heavy-ion collisions was historically considered one of the signatures of QGP formation. However, recent measurements in proton-proton (pp) and proton-lead (p-Pb)...
We study the thermal properties of scalar quantum field theories (QFTs) involving 3-leg and 4-leg interaction terms, with special attention on the role of bound states and resonances. Within a suitable unitarization scheme, for which the employed QFT is unitary, finite, and well defined for each value of the coupling constant, we calculate the scattering phase shifts, whose derivatives are...
Jets are collimated sprays of particles produced from the fragmentation and hadronization of hard-scattered partons in high energy hadronic and nuclear collisions. Jet properties are sensitive to details of parton showering processes and expected to get modified in the presence of a dense partonic medium. Recently features similar to those in heavy-ion collisions have been observed in high...
In ultra-central heavy-ion collisions, the effects of event-by-event fluctuations on anisotropic flow are relatively more pronounced due to less geometrical anisotropy of initial transverse profiles. The magnitudes of elliptic flow $v_2$ and triangular flow $v_3$ were reported to be almost the same value in ultra-central collisions [1]. Dynamical models based on relativistic viscous...
Jets are excellent probes for the study of the deconfined matter formed in heavy ion collisions. In particular, jet substructure measurements can help us understand the interaction dynamics of high-energy partons with the quark-gluon plasma. We introduce a new infrared and collinear safe observable: jet energy flow measurements using jets reconstructed with different resolution parameters $R$....
The strongly intensive quantity $\Sigma$ is a new observable, introduced recently to the domain of heavy-ion physics. In superposition models which assume independent particle production from statistically identical sources, $\Sigma$ is insensitive to the number of sources and its fluctuations, contrary to the standard forward-backward correlation coefficient ($b_{\rm corr}$). Therefore, it...
In relativistic heavy ion collisions, the event-by-event mean transverse momentum ($\langle{p_{T}}\rangle$) fluctuations are sensitive to fluctuations in overlap area and reflect the nature of initial-state fluctuations in energy density. We present a cumulant framework to measure the event-by-event $\langle{p_{T}}\rangle$ fluctuations up-to $4^{\mathrm{th}}$ order which is then validated...
Short-lived hadronic resonances are very useful to probe the late-stage evolution of ultra-relativistic heavy-ion collisions. Since their lifetimes are comparable to the hadronic phase timespan, their measured yields are modified via rescattering and regeneration processes. The suppression of the K$^{*0}$/K ratio in central Pb--Pb collisions compared to pp interactions already hints at the...
Heavy-flavour (charm and beauty) jets are excellent probes to study Quantum Chromodynamics (QCD). Their precise measurements in proton-proton collisions are used to verify perturbative QCD calculations and improve our modelling capabilities by constraining Monte Carlo generators. They also serve as the reference measurements for more complex systems such as Pb–Pb collisions, helping to...
Hydrokinetic formalism is a deterministic set of relaxation type equations that tracks the evolution of n-point correlation functions of stochastic hydrodynamic quantities. Hydrokinetic formalism is a complementary approach to solving the Stochastic Differential Equations (SDE) for fluctuating hydrodynamics. Hydrokinetics is comparatively easier to solve than the SDEs, which need to deal with...
Relativistic hydrodynamics has been successful in describing the evolution of Quark-Gluon Plasma, as well as understanding and predicting experimental measurements highlighting the collective behavior of the observed hadrons created in relativistic heavy-ion collisions. In parallel with the remarkable progress made in numerical fluid dynamics, the study of analytical solutions remains helpful...
Recent results in high-multiplicity pp collisions show interesting features similar to those that are associated to the formation of a quark-gluon plasma in heavy-ion collisions [1]. Investigating the modification of the intra jet properties as a function of event multiplicity in pp collisions can provide deeper insight into the nature of these effects.
We will present the latest...
Very recently, a non-equilibrium effective field theory framework has been formulated for fluctuating hydrodynamics [1]. In this talk, we present examples of applying this novel formalism to study the properties of QCD-like systems. In the first example, we study the dependence of the conductivity/resistivity on the external magnetic field in a chiral medium (the constituent of which includes...
The ratio of strange to non-strange hadron yields increases from low- multiplicity to high-multiplicity hadronic interactions, reaching values observed in heavy-ion collisions. The ALICE experiment investigates the microscopic origin of this striking phenomenon by performing dedicated multi-differential analyses in pp collisions at $\sqrt{s}$ = 13 TeV.
To separate strange hadrons...
The measurement of azimuthal correlations between two particles is a powerful tool to investigate the properties of strongly-interacting nuclear matter created in ultra-relativistic heavy-ion collisions. In particular, studying the near-and away-side hadron yields associated with trigger particles can provide important information to understand both the jet-medium interaction and hadron...
The study of collective phenomena in ultrarelativistic heavy-ion collisions is nowadays to a great extent built on the so-called flow amplitudes $v_n$ and symmetry planes $\Psi_n$. Both appear as two distinct degrees of freedom in the parametrization of the azimuthal distribution of the produced particles, which is used in the study of the quark-gluon plasma (QGP). Investigating the complex...
In this talk I review recent progress in resummed perturbative calculations of the equation of state of QCD and N=4 supersymmetric Yang-Mills (SUSY) theory. In the case of QCD, I will review progress that has been made using hard-thermal-loop perturbation theory (HTLpt) at finite temperature and quark chemical potential(s), focussing on recent NNLO HTLpt predictions for the quadratic and...
The interplay of the chiral anomaly and the strong magnetic field (~10$^{15}$ T) created in the off-central heavy-ion collisions could give rise to a collective excitation in the quark-gluon plasma called the Chiral Magnetic Wave (CMW), which can be experimentally sought by the charge asymmetry ($A_{\rm ch}$) dependence of elliptic flow $v_2$ of positively and negatively charged hadrons....
The phase transition from hadronic matter to quark-gluon plasma (QGP) is a phenomenon that occurs under extreme conditions of high temperature and high density, as achieved at the relativistic heavy ion collider (RHIC). The QGP causes energy loss of high momentum particles which is observed as suppression of high momentum hadron production in A+A collisions relative to p+p collisions. The...
This talk presents a novel instability in the Chern-Simons (or axionic) magnetohydrodynamics (MHD), arising from the spatial inhomogeneity of the axion-like field. In particular, this instability amplifies the Alfven waves in certain regions of spacetime in a way that is clearly parity-violating. The Aflven velocity reaches the speed of light in such regions, but it never exceeds it.
Internal properties of jets and their production in small collision systems (pp and p--Pb) are tightly connected to perturbative and non-perturbative aspects of quantum chromodynamics (QCD), such as cold nuclear matter effects. Recent studies of high-multiplicity final states of small collision systems also exhibit signatures of collective effects that are thought to be associated with hot and...
First six cumulants of proton number are calculated in the statistical resonance gas model with chemical potentials for every stable identified hadron species. The chemical potentials are chosen in such a way that the average particle numbers after decay of resonances are kept constant independently of temperature and equal to the values given at the chemical freeze-out. This corresponds to a...
In this contribution, we present a first factorial moment analysis performed on the multiplicity distributions of charged particles produced in the Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}$=2.76 TeV, recorded with the ALICE detector at the LHC. The normalized factorial moments (NFM) of spatial configurations of charged particles in two-dimensional angular ($\eta,\varphi$) phase space,...
Direct photons are widely used probe to study the properties and evolution of the hot and dense medium (e.g. QGP) produced in high energy heavy-ion collisions. Being color neutral, they do not interact strongly with the medium and are produced at all stages of the collision.
A universal scaling of the direct photon yield with charged particle multiplicity has been observed for a wide range...
Recent measurements in high multiplicity proton-proton collisions have shown the emergence of several features that are reminiscent of QGP phenomenology, one of which is the enhanced production of strange and multi-strange hadrons. Strange hadron production represents a key probe to study QGP formation in hadronic collisions as well as to understand the mechanisms behind hadronisation.
In...
Non-equilibrium Green’s functions provide an efficient way to describe the pre-equilibrium evolution of macroscopic quantities in early stages of heavy-ion collisions.
Within the kinetic theory framework we use moments of the distribution functions to calculate time dependent non-equilibrium Green’s functions describing the evolution of initial energy/momentum/charge perturbations [1]. Using...
With the tremendous accomplishments of RHIC and the LHC experiments and the advent of the future Electron-Ion Collider on the horizon, the quest for compelling evidence of the color glass condensate (CGC) has become one of the most aspiring goals in the high energy quantum chromodynamics research. Pursuing this question requires developing the precision test of the CGC formalism. By...
We develop a general decomposition of an ensemble of initial density profiles in terms of an average state and an orthonormal basis of modes that represent the event-by-event fluctuations of the initial state. The basis is determined such that the probability distributions of the amplitudes of different modes are uncorrelated. Based on this decomposition, we quantify the different types and...
Measurements of strange hadron production in pp and p-Pb collisions had been used as a reference for the study of the so-called strangeness enhancement effect, occurring in heavy ion collisions where QGP formation is observed.
Recently, the ALICE Collaboration studied strangeness production in pp interactions, unveiling unexpected features in the strange hadron to pion yield ratios. These...
The jet transverse momentum diffusion coefficient $\hat{q}$ is an important transport coefficient governing the radiative energy loss of a parton propagating the Quark-Gluon Plasma (QGP) created in Heavy-Ion Collisions. Based on perturbative arguments [1], which were recently extended to next-to-leading order [2], the dimensionless ratio $\hat{q}/T^3$ was shown to be connected with the...
Multiplicity distributions in e+e- and pp collisions analysed via combinants exhibit oscillatory behavior of the modified combinants. The possible sources of these oscillations and their impact on our understanding of the multiparticle production mechanism were discussed [1-3]. The set of combinants, Cj provides a similar measure of fluctuations as the set of cumulant factorial moments, Kq,...
Exploring the shape of the pair-source function for particles such as pions or kaons has been 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, since no direct measurement is possible, femtoscopic (momentum) correlations are utilized to gain...
Previous ALICE results indicate a stronger than linear increase of the inclusive normalized J/$\psi$ yield with charged-particle multiplicity, both measured at mid-rapidity, in proton-lead collisions at $\sqrt{s_{NN}}=5.02$ TeV. The corresponding ALICE results on proton-proton collisions at$\sqrt{s}=13$ TeV provide a clearer picture of a stronger than linear increase.
In PYTHIA8, this...
Two-particle differential correlators of particle numbers ($R_2$) and particle transverse momenta ($P_2$ and $G_2$), recently measured in Pb-Pb collisions, emerged as powerful tools to gain insights into particle production mechanisms and infer transport properties such as the ratio of shear viscosity to entropy density of the medium created in Pb-Pb collisions. In this talk, recent ALICE...
Since the first positive measurement of the Λ-hyperon global spin polarization in heavy-ion collisions by STAR collaboration in 2017, the understanding of the nature of this phenomenon is one of the most intriguing challenges for the heavy-ion physics community. As relativistic fluid dynamics celebrates multiple successes in describing collective dynamics of the QCD matter in such reactions,...
The pre-hydrodynamic evolution of a heavy-ion collision can have a considerable effect on final state observables, notably those related to the transverse momentum spectra of final particles [1]. In this work, we study two different collision systems, namely Pb-Pb and p-Pb, utilising a state-of-the-art hybrid model. We extend our previous results [1] on the effects of pre-hydrodynamical models...
The ALICE Collaboration presents results of a search for jet quenching effects in high multiplicity pp collisions at $\sqrt{s} = 13~\rm{TeV}$ by measuring the semi-inclusive acoplanarity distribution of charged-particle jets that recoil from a high transverse momentum trigger-track. The search for jet quenching is performed by comparing the acoplanarity distributions measured in high...
The McLerran-Venugopalan Model (MV) of Color Glass Condensate for two colliding nuclei has been solved in the past using numerical methods and recursive analytic solution. On the other hand, in the weak field limit explicit analytic solutions in transverse momentum space have, in principle, been known for quite some time. Based on the latter we derive analytic expressions for gluon 2-point...
We explore the thermalization of energetic partons in quark-gluon plasma medium by analyzing the medium response effect on jet substructure observables. In high-energy heavy-ion collisions, jets become more populated by soft partons through the induced radiation and scatterings in the medium. Consequently, the energies of some soft jet partons reach the typical energy of the medium...
Measurements of neutral mesons in small collision systems can serve as a baseline to understand modifications in heavy-ion collisions, where a QGP is formed.
These measurements can also be used to test pQCD predictions and to constrain fragmentation functions as well as parton distribution functions.
Furthermore, a good understanding of particle production enables the measurement of direct...
Measurements of long-range correlations are one of the important tools for evaluation of the interplay between the initial- and final-state effects. Recently, non-vanishing second Fourier harmonic $\it{v}_{2}$ has been observed in small collision systems such as pp and p--Pb collisions. In this contribution, we present measurements of $\it{v}_{2}$ extracted from long-range two-particle...
We study theoretical uncertainties in the hydrodynamic description of relativistic heavy-ion collisions by examining the full nonlinear causality conditions [1] and quantifying their effects on flow observables [2]. The causality conditions impose physical constraints on the maximum allowed values of inverse Reynolds numbers during the hydrodynamic evolution. We develop a new numerical scheme...
The determination of the hot QCD pressure has a long history, and has --
due to its phenomenological relevance in cosmology, astrophysics and heavy-ion collisions — spawned a number of important theoretical advances in perturbative thermal field theory applicable to equilibrium thermodynamics.
In particular, the long-standing infrared problem that obstructs the perturbative series has been...
The electromagnetic fields produced by non-central heavy ion collisions are extremely powerful and give rise to a plethora of fascinating subjects in strongly interacting matter. Their evolution is a significant and unresolved issues. Because the relaxation time of the hot QCD matter to the electromagnetic fields is comparable with the lifetime of external electromagnetic field, we question,...
We argue that a detailed analysis of the spin aligement of vector mesons can serve as a probe of some aspects of spin dynamics in the vortical fluid for which there have been quite a few theoretical developments but relatively little phenomenology:
The degree of relaxation between vorticity and parton spin polarization, and the degree of coherence of the hadron wavefunction at...
Quarks and gluons traversing a QCD medium may lose energy through a variety of processes, including medium-induced radiation sensitive to their QCD color factor.
The color-charge dependence of the parton-medium interaction is a critical component in all jet energy loss models and generally in heavy-ion physics phenomenology. In this talk, the color charge dependence of jet-medium...
We study fluctuations of particle number in the presence of critical point by utilizing molecular dynamics simulations of a classical Lennard-Jones fluid in a periodic box. The numerical solution of the $N$-body problem naturally incorporates all the relevant effects like physics of the correlation length, exact conservation laws, and finite size effects, allowing us to study the luctuation...
NA61/SHINE is a fixed-target experiment at the CERN SPS. Its spectrometer has unique properties including large particle acceptance and precise momentum measurement. These properties together with high statistics of collected proton-proton collisions at beam momentum 158 GeV/c allow analyzing the transverse polarization of $\Lambda$ hyperons produced in the primary vertex.
The opportunities...
The theory of jet quenching has been steadily evolving in order to incorporate the effects of having a longitudinally evolving plasma. On the other hand, the transverse dynamics of the medium evolution has been largely ignored due to the fact that its effects are suppressed by powers of the energy of the probe. Recently, a calculation of the effects of medium motion on transverse momentum...
In this talk, we present a study of direct photons in relativistic nuclear collisions, along with the production of hadrons, from RHIC Beam Energy Scan (BES) to LHC energies. Thermal photons are soft and penetrating probes of the strongly-coupled nuclear matter created in relativistic heavy-ion collisions. Their spectrum and momentum anisotropies remember the QGP’s chemistry evolution and its...
Two-component hydrodynamic model with jets, HYDJET++, is employed to analyse the data on elliptic flow correlations at low (pT < 1.25 GeV/c) and high (pT > 14 GeV/c) transverse momenta in Pb+Pb collisions at \sqrt{sNN} = 5.02 TeV. Because of these two mechanisms, describing soft and hard processes, the model calculations restored by the four-cumulant method reproduce the centrality dependence...
We develop a new parametric 3-dimensional initial condition for low-energy heavy-ion collisions based on collision geometry for a multistage hybrid framework. The longitudinal structure of the collision profile is constrained by rapidity-dependent experimental measurements, especially the directed flow of pions and protons (i.e., $v_1(y)$). We introduce a baryon stopping parameter which...
Nuclear deformation is an ubiqutous phenomenon for most atomic nuclei, reflecting collective motion induced by interaction between valance nucleons and shell structure. In most cases, the deformation has a quadrupole shape that is charactorized by overall strength $\beta_2$ and triaxiality $\gamma$ (prolate $\gamma=0$, obolate $\gamma=\pi/3$ and triaxial otherwise). Collisions of deformed...
Increasingly many studies have involved the use of Bayesian statistics in estimating the transport properties of quark-gluon plasma through hydrodynamic calculations. So far, most of these studies have obtained their estimates in Pb-Pb collision systems at varying center-of -mass energies. It has been since learned that the inclusion of multiple collision configurations and high harmonic...
Two-particle correlations are a widely used tool for studying relativistic nuclear collisions. Multiplicity fluctuations have been studied as a possible signal for QGP and the QCD critical point. Momentum correlations and covariances of momentum fluctuations, which arise from the same correlation function, have also been used to extract properties of the nuclear collision medium such as the...
Building upon Ref. [1], we present an improved three-dimensional dynamical initialization model for heavy-ion collisions, implementing local energy-momentum conservation and baryon charge fluctuations at string junctions [2]. These improvements lead to an excellent description of the charged hadron and net proton rapidity distributions in Au+Au collisions from 7.7 to 200 GeV [3]. Based on...
The quark-gluon plasma formed in heavy-ion collisions has a large momentum anisotropy, especially during early stages of collisions. For jet partons this leads to momentum broadening which is not isotropic in the parton's transverse plane. In this talk we discuss such anisotropic momentum broadening of jets in detail and evaluate how it changes the radiation of hard gluons, and gives rise to a...
Measuring the jet substructure in heavy-ion collisions provides exciting new opportunities to study detailed aspects of the dynamics of jet quenching in the hot and dense QCD medium created
in these collisions. In this talk, we present new ATLAS measurements of jet substructure performed using various jet (de)clustering and grooming techniques. Measurements of inclusive jet suppression...
Despite almost a decade of work, the absence of jet-modification in small systems is yet to be satisfactorily explained. Although JEWEL (Jet Evolution With Energy Loss) is a Monte Carlo (MC) generator designed to study the evolution of jets with a variety of background media, the publicly available versions are not able to simulate small systems. We present the first results using an...
The ALICE experiment has significantly upgraded its detectors. It will make possible to perform new measurements in the Ultra Peripheral Collisions (UPCs) of lead nuclei for the integrated luminosity of $\mathcal{L}^{\rm Pb-Pb}=13$/nb during Run 3 and Run 4. For Run 5 and beyond, a completely new next-generation heavy-ion experiment ALICE 3 is proposed. The new detector system will cover
much...
The Compressed Baryonic Matter (CBM), currently under construction at the Facility for Anti-proton and Ion Research (FAIR) accelerator complex in Darmstadt, Germany aims to explore the QCD phase diagram at high baryon densities. Till date, no dilepton data have been collected in heavy-ion collisions at beam energies between 2A and 40A GeV. CBM aims to perform pioneering measurements of lepton...
We discuss mean field theory of Quarkyonic matter at zero temperature. this field theoretical description of quarkyonic matter consisting of quark, nucleon and ghost fields. The ghosts are present to cancel over-counting of nucleon states that are Pauli blocked by the quark Fermi sea. We treat the nucleons with contact interactions in mean field approximation and the quarks without mean field...
Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\Delta\eta$ that are strikingly similar to those seen in heavy-ion collisions.
In larger systems, the long-range correlations are known to arise from the collective dynamics of the produced quark-gluon plasma (QGP). The similarity between the $pp$ and heavy-ion measurements raises...
Recently, the so-called relative transverse activity classifier, $R_T$, has been proposed as a tool to disentangle the particle production originated from the soft and hard QCD processes in proton-proton (pp) collisions. $R_T$ is a useful quantity to study particle production in events with exceptionally large or small activity in the transverse region with respect to the event-averaged...
High-pt theory and data are traditionally used to explore high-pt parton interactions with QGP, while bulk QGP properties are commonly explored through low-pt data. However, rare high-pt light and heavy flavor can also be a powerful tool for inferring bulk QGP properties, as they are sensitive to global QGP parameters. A prerequisite for such QGP tomography is a proper description of high-pt...
The photon-photon interaction in ultra-relativistic heavy-ion collision is a source of the $(e^+,e^-)$ pairs. The photon-photon fusion leads to the lepton creation in the broad configuration space around ''collision'' point. Those created close to heavy nuclei may undergo strong interaction with them.
The impact parameter space distributions of electrons and positrons are calculated within...
The influence of initial state fluctuations on elliptic e2 and triangular e3 eccentricities and on elliptic v2 and triangular v3 flows in relativistic heavy ion collisions is studied within three Monte Carlo models. The models are based on (i) number of participant nucleons, (ii) number of binary collisions, and (iii) partonic energy density in color glass condensate (CGC) phase,...
The Quark-Gluon Plasma, a state of matter characterized by its extreme energy density and temperature generated in heavy-ion collision experiments, is expected to modify hard-scattered partons traveling through it and, consequently, the jets they produce. Analyses regarding jets may recover information about the medium and its partonic energy-loss mechanism. This work applies the Monte Carlo...
We present a comparison of observables related to photon-triggered jets for different collision energy systems, at LHC and RHIC energies, with the latest update of the JETSCAPE framework [1,2]. In heavy-ion collisions, multiple probes are used to study the properties of the Quark-Gluon Plasma (QGP). Photons can be produced at any stage of the heavy-ion collision. Since photons do not interact...
We demonstrate that hard dijet production via inelastic diffraction is a promising channel for probing gluon saturation at the Electron-Ion Collider. Diffraction refers to a process in which there is a large rapidity gap between the produced jets and the nuclear target, while inelastic means that the two hard jets - a quark-antiquark pair generated by the decay of the virtual photon - are...
The measurement of hadronic resonance production in heavy-ion collisions at the LHC has led to the observation of a prolonged hadronic phase after hadronisation. Due to their short lifetime, resonances experience the competing effects of regeneration and rescattering of the decay products in the hadronic medium. Studying how the experimentally measured yields are affected by these effects can...
Hard probes, due to their large momenta (or masses), are produced only through hard interactions with large momentum transfer at the earliest phase of a heavy-ion collision. They then propagate through the evolving medium probing QCD matter at different energy scales and different phases of the fireball evolution. During this propagation heavy quarks and high-$p_T$ partons lose a substantial...
The production of (anti)deuterons in relativistic heavy-ion collisions is currently well described by two models that point to different mechanisms of particle creation. The first of the two, the coalescence model, describes the (anti)deuteron’s creation as a result of final-state interactions among (possibly off-shell) nucleons after the chemical freeze-out. The second, the thermal model...
“Hybrid Hadronization” is a Monte Carlo package that hadronizes systems of partons. It smoothly combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems, following the picture outlined by Han et al. [PRC 93, 045207 (2016)]. Hybrid Hadronization can be applied to a variety of systems from...
Jet substructure applied to a heavy-ion environment can provide valuable information about jet-medium interaction. This class of observables, mostly inherited from proton-proton collisions, is still far from being fully exploited as a tool for QGP tomography. So far, measurements are restricted to quantities that provide an average quantification of the medium parameters, missing the critical...
Because photons and dileptons are unlikely to interact after production within a quark-gluon plasma (QGP), they can probe the inner dynamics of this strongly interacting system. To leading order in the electromagnetic coupling and all orders in the strong coupling, the observable emission rates can be determined from the QCD vector channel spectral function. The resummed next-to-leading order...
Recently the splitting of elliptic flow $v_2$ at finite rapidities has
been proposed to be the result of global vorticity in non-central
relativistic heavy ion collisions [1]. Here we confirm the existence
of the $v_2$ splitting. However, we show that this left-right $v_2$
splitting (on opposite sides of the impact parameter axis) is mostly
due to the non-zero directed flow $v_1$ at...
We present a study of photon-photon scattering in the mass range $W_{\gamma \gamma}<5$ GeV. We extend earlier calculations of this cross section for $W_{\gamma \gamma}>5$~GeV into the low mass range where photoproduction of the pseudoscalar resonances $\eta$, $\eta'(958)$ contributes to two-photon final states. We present the elementary photon-photon cross section as a function of diphoton...
Because of the increasing gluon density towards small-$x$, a regime where these densities reach a saturation ($Q_{\rm sat}$) is expected. The observation of this gluon saturated matter has several consequences to particle production and is a matter of an entire effective field theory, the Color Glass Condensate. The Large Hadron Collider beauty (LHCb) experiment has a privileged geometry for...
Jets produced in heavy-ion collisions provide important information about the medium that they traverse. Their seeds, highly energetic partons that are created via hard scatterings during the collision, are affected by all different stages of the medium, including the pre-equilibrium precursor state of the quark-gluon plasma, which is known as the glasma. We will report on our numerical...
We revisit the picture of jets propagating in the quark-gluon plasma. In addition to vacuum radiation, related to the high initial virtuality of a jet, jet particles scatter on the medium constituents resulting in induced emissions. Analytical approaches to resumming these interactions have traditionally dealt separately with multiple, soft [1,2], or rare, hard scatterings [3,4]. A full...
The BEST collaboration’s equation of state (EoS) maps a 3D Ising model onto the lattice QCD EoS but contains 4 free parameters related to the size, location, and spread of the critical region across the QCD phase diagram. However, certain combinations of those 4 free parameters lead to acausal ($c_s^2>1$) or unstable ($\chi_2^B<0$) realizations of the EoS that should not be considered. Here,...
The aim of this work was to investigate the properties of a new, simple model of the nucleus+nucleus collisions at high energy, and its applicability to the CERN SPS energy regime. The model was uniquely based on the system's geometry and local energy and momentum conservation in the quark gluon plasma produced in the reaction.
We studied Pb+Pb collisions at $\sqrt{s_{NN}}$ = 17.3 GeV and...
The study of femtoscopic correlations of photon pairs, emitted from heavy-ion collisions, can serve as an unique probe of the evolution of the source in space and time. Unlike commonly used charged particles photons are not subject to strong, nor electromagnetic interactions. These properties imply no distortion of the information carried by $γ$ from the point of their creation up to the...
Recently, we developed a framework to evaluate the single-inclusive gluon emission spectrum without further assumptions, including full resummation of multiple scatterings. In this talk, we compare this formalism with well-known analytical approximations, determining in that way their validity in all kinematical regions and showing to what extent accounting for multiple scatterings is crucial...
Jet modification is a multi-stage (multi-scale) process: an initial high virtuality stage gives way to a lower virtuality transport stage for high energy partons, and a strongly coupled phase for lower energy parts of the shower. The transition from the high virtuality medium-modified DGLAP stage takes place when the virtuality reaches the medium induced scale 𝑞̂ 𝜏, where 𝜏 is the lifetime of...
The lepton pair production in ultraperipheral collisions is studied in the classical field approximation. We derive a general form of the cross section in terms of photon distributions that depend on the transverse momentum and coordinate based on the wave packet form of nuclear wave functions. Such a general form of the cross section in the classical field approximation contains the results...
Direct photons are a useful probe to study the properties of QGP and the dynamic evolution of the collision system as they do not interact with the medium strongly. Low transverse momentum direct photons are believed to originate primarily from thermal radiation, however, calculations of thermal photon emission fall short in describing the measured direct photon yield and the anisotropy at the...
Quantum Chromodynamics (QCD), the theory of strong interactions, predicts that at sufficiently high temperature and/or high energy density normal nuclear matter converts into a deconfined state of quarks and gluons, known as the Quark-Gluon Plasma (QGP). To investigate the phase diagram of QCD matter, the Relativistic Heavy Ion Collider (RHIC) started the first phase of the Beam Energy Scan...
The search for the Quantum Chromodynamics (QCD) critical point is underway at the Relativistic Heavy-Ion Collider (RHIC) Beam Energy Scan II. The primary signature of the critical point is a peak (divergence) in the kurtosis of the net-proton number distribution, $\kappa_4$. Most previous studies of kurtosis have focused on equilibrium physics, whereas it is well-known that out-of-equilibrium...
The injection of energy and momentum from a jet into the QGP generates a wake, which leads to soft and semi-hard particle creation correlated with the jet direction after the QGP hadronizes. As several jet quenching studies have shown, this medium response phenomenon plays a crucial role in our understanding of many jet structure and substructure observables. Nevertheless, a detailed account...
The temperature and size of the quark-gluon plasma that is created in heavy-ion collisions are properties that are to be experimentally constrained. This can be done via direct photon Hanbury Brown and Twiss (HBT) measurements that are able to both quantify the excess of thermal photons as well as the size of the emitting source. In contrast to femtoscopic measurements of bulk particles, this...
We probe the origin of strangeness enhancement by separating the strange particles produced in hard processes (jets) from those produced in soft processes (bulk) using the measurement of triggered hadron-$\phi$(1020) and hadron-$\Lambda$ angular correlations. Separating these measurements by event muliplicity in p-Pb collisions allows one to measure the effects of increasing system size on...
Electrons constitute an essential component of final states from the leptonic decay channels of W and Z bosons. Their reconstruction and identification are especially challenging in heavy-ion collisions due to high detector occupancy. Therefore, the evaluation of electron performance is crucial for precision measurements of properties of quark-gluon plasma produced in heavy-ion collisions at...
The study of nucleon-nucleon (N-N), nucleon-hyperon (N-Y), and hyperon-hyperon (Y-Y) interactions are fundamental to understanding the physics of relativistic heavy-ion collisions and neutron stars the existence of various exotic hadrons. Geometry and dynamics of the particle-emitting source in heavy-ion collisions can be inferred via the femtoscopy method. Two-particle correlations at small...
Near perfect fluid behavior is a hallmark signature of the quark gluon plasma (QGP), however, how this behavior emerges is still not fully understood. Thus, measurements of many different particles over a wide rapidity range are needed to understand this phenomenon. Heavy quark flow is expected to be different from light quark flow due to their larger masses, making heavy flavor flow...
We present the latest predictions for several QCD processes at low-x in the color dipole picture which are of interest for current hadron-hadron and future electron-hadron colliders. The predictions are derived using the solution to the Balitsky-Kovchegov equation for proton and nuclear targets with the collinearly improved kernel and including the impact-parameter dependence. Two different...
Ultra-relativistic collisions of small nuclear systems can shed light on the onset of QGP formation. So far, proton-nucleus (p+A) and deuteron-nucleus (d+A) collisions have been used to study the emergence of the smallest QGP droplets, producing the puzzling results that the non-zero elliptic flow of hadrons at intermediate transverse momenta is not correlated to the suppression of their...
Partonic jets, i.e. highly energetic collimated sprays of strongly interacting particles, provide an excellent means to study the hot and dense medium
of a quark gluon plasma (QGP), since the highly energetic jet particles interact with the medium particles, however do not thermalize.
Jet particles in the medium undergo both processes of scatterings off medium particles as well as emission...
We have derived the chiral kinetic theory (CKT) with collisions in a QED matter. We have discussed the global equilibrium conditions in the presence of collisions. Then, we implement the CKT with effective collision term in the moment expansion and derive the off-equilibrium corrections to the axial currents and spin polarization vector.
Bulk matter produced in heavy ion collisions has multiple
conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process
of these charges can be described by a diffusion matrix describing the interdependence of diffusion of
different charges. The diffusion coefficient matrix is estimated here from the Boltzmann kinetic theory
for the hadronic phase...
We present a consistent photon production calculation from hadronic cross sections, including bremsstrahlung and 2-to-2 reactions, matching the usually employed thermal rates [1]. Using the hadronic transport approach SMASH as the afterburner for the hadronic stage at RHIC and LHC energies, we find a significant increase in the calculated momentum anisotropies of these photons due to...
We present, for the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both pomeron-lead and pomeron-proton topologies. The analysis is performed over 10.4 units of pseudorapidity at a nucleon-nucleon center-of-mass energy of 8.16 TeV, i.e. almost 300 times higher than previous measurements of diffractive production in proton-nucleus collisions. For...