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a) v2(pt) for the centrality bin 40%–50% from the 2- and 4-particle cumulant methods for this measurement and for Au-Au collisions at sNN=200 GeV. (b) v2{4}(pt) for various centralities compared to STAR measurements. The data points in the 20%–30% centrality bin are shifted in pt for visibility.
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We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at sqrt[S(NN)] =2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|η|<0.8) and transverse momentum range 0.2<p t<5.0 GeV/c. The elliptic flow signal v₂, measured using the 4-parti...
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We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at sNN=2.76TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|eta|
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Measurements of charge-dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at root s(NN) = 2.76 TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudorapidity range vertical bar eta vertical bar < 0.8 are presented as a function of the collision centrality, particle separ...
Citations
... Anisotropic flow measurements at RHIC and the LHC have shown that the QGP behaves as a near-perfect liquid [8][9][10][11][12][13][14][15][16][17][18], with a shear viscosity over entropy density ratio close to the lowest limit predicted by AdS/CFT theory [19]. The anisotropic flow studies are typically performed via multi-particle azimuthal correlations [20], providing insight into various aspects of QGP dynamics. ...
Multi-particle correlations between azimuthal angle and mean transverse momentum are a powerful tool for probing size and shape correlations in the initial conditions of heavy-ion collisions. These correlations have also been employed to investigate nuclear structure, including potential nuclear shape phase transitions at the energy frontier. However, their implementation is highly nontrivial, and prior studies have been mostly limited to lower-order correlations, such as the modified Pearson correlation coefficient, . This paper presents a unified framework that employs a recursive algorithm, enabling the efficient evaluation of arbitrary-order correlations while maintaining computational efficiency. This framework is demonstrated using widely adopted transport models, including AMPT and HIJING. The proposed unified algorithm for multi-particle correlations between azimuthal angle and transverse momentum provides a systematic and efficient approach for multi-particle correlation analyses. Its application in experiments at the Relativistic Heavy Ion Collider and the Large Hadron Collider facilitates the exploration of nuclear structure at ultra-relativistic energies.
... One of the foremost signals of the formation of a quarkgluon plasma (QGP) during a heavy ion collision is the elliptic flow of the bulk medium [1][2][3][4][5], in semicentral collisions. 1 Due to the geometry of the collision, the overlap region of the two nuclei is not circular, and contains azimuthal anisotropies in density. Pressure gradients created by these spatial inhomogeneities lead to azimuthal anisotropies in the momentum distribution [6], quantified by the Fourier coefficients of the differential hadronic yield, ...
... To further explore the azimuthal anisotropies arising from TMDPDFs, we compute higher order harmonics v 3 and v 4 , which are displayed in Fig. 11. The experimental results of v 3 and v 4 display a different behavior than v 2 . While v 2 starts decreasing with p T already at p T 5 GeV, v 3 and v 4 are increasing up to the highest data points (p T 10 and p T 4, respectively). ...
... The experimental results of v 3 and v 4 display a different behavior than v 2 . While v 2 starts decreasing with p T already at p T 5 GeV, v 3 and v 4 are increasing up to the highest data points (p T 10 and p T 4, respectively). However, the data display large uncertainties at high p T and are limited to p T 10 GeV. ...
Various azimuthal anisotropies ( v 1 , v 2 , v 3 , v 4 ), at high transverse momentum (high p T ), are shown to arise from the asymmetric scattering of transverse polarized quarks and gluons, arising from unpolarized nucleons (the Boer-Mulders effect) and resulting in unpolarized hadrons (the Collins effect). Combined with the asymmetric scattering of partons from polarization independent but transverse momentum dependent (TMD) distributions, we obtain a possible mechanism to understand the azimuthal anisotropy of hadrons at large transverse momentum observed in p − p collisions. Constraining the ratio of polarization dependent TMD distributions to polarization independent distributions by comparing with the data from p − p collisions, we find that scaling the acquired transverse momentum of the initial state partons from the proton, due to prescattering before the hard interaction, with the length of the nucleus ( k ⊥ 2 ∝ A 1 / 3 ), straightforwardly yields the azimuthal anisotropy at high p T in p − A collisions.
Published by the American Physical Society 2025
... Not only does it provide a window into the properties of strongly interacting matter but also serves as a key observable in constraining theoretical models of collision dynamics. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] An elliptic flow, denoted by 2, measures the anisotropic distribution of particles produced in the azimuthal direction with respect to the reaction plane ( rp) in heavy-ion collisions. This is defined as the second Fourier coefficient in the Fourier decomposition of the par-ticle yield as a function of the azimuthal angle: [1] ...
Significant differences exist in the elliptic flow v2 for particles and their corresponding anti-particles. These differences, which are more significant for baryons and anti-baryons, were observed from the solenoidal tracker (STAR) experiment during Beam Energy Scan I (BES-I) at relativistic heavy ion collider (RHIC). By employing the simulated many-accelerated strongly interacting hadrons (SMASH) model, we studied the v2 differences between protons and anti-protons as well as between Λ and Λ¯ in Au + Au collisions at sNN=7.7 GeV as a function of the evolution time. It was found that as the evolution time increases, the v2 differences between protons and anti-protons become more significant than those between Λ and Λ¯ . This phenomenon can be explained by the different constituent quarks of protons and Λ. Given that some of the u and d quarks come from the colliding nuclei and are transported to midrapidity, they undergo more interactions than the produced quarks, resulting in protons Δv2 being larger than Λ Δv2. We compared the SMASH calculations with STAR BES-I data and concluded that higher-precision data from BES-II will set constraints on theoretical frameworks to interpret the v2 differences between particles and anti-particles.
... Finite azimuthal anisotropy has been well observed in heavy-ion collision experiments so far * e-mail: Barnafoldi.Gergely@wigner.hun-ren.hu at RHIC and LHC energies up to higher-order cumulants with various analysis methods [3][4][5][6]. Here, we present our deep learning feed-forward network for estimating elliptic flow (v 2 ) coefficients, which we compare to heavy-ion collision data from RHIC to LHC energies. ...
We developed a deep learning feed-forward network for estimating elliptic flow (v2) coefficients in heavy-ion collisions from RHIC to LHC energies. The success of our model is mainly the estimation of v2 from final state particle kinematic information and learning the centrality and the transverse momentum (pT) dependence of v2 in wide pT regime. The deep learning model is trained with AMPT-generated Pb-Pb collisions at √sNN = 5.02 TeV minimum bias events. We present v2 estimates for π±, K±, and p + p¯ in heavy-ion collisions at various LHC energies. These results are compared with the available experimental data wherever possible.
... The QGP is an extremely hot and dense system where (anti-)quarks and gluons exist as deconfined, quasi-free partons. Past comparisons between experimental anisotropic flow measurements and theoretical models (i.e., hydrodynamics [3][4][5] and kinetic transport methods [6-9]) suggest that the QGP behaves like a near-perfect fluid with a very small shear-viscosity to entropy-density ratio above the KSS lower bound η/s = 1/(4π) (ℏ = k B = c = 1) [10]. At temperatures exceeding the Hagedorn temperature, T H ≃ 150 MeV [11], the partons in the QGP resemble an ideal thermal gas. ...
... The cooling of the thermalized QGP can be modeled using Newton's cooling law, assuming an exponential decay of the temperature over time. This approximation is consistent with the rapid expansion and cooling dynamics observed in heavy-ion collisions [1][2][3][4][5]. Using the boundary conditions T = 550 MeV at t = 0 fm/c and T = 150 MeV at t = 10 fm/c, the temperature as a function of time is given by ...
Transport properties of the quark-gluon plasma are instrumental to testing perturbative quantum chromodynamics and understanding the extreme conditions of relativistic heavy-ion collisions. This study presents an analytical investigation of the shear viscosity and the shear viscosity-to-entropy density ratio of the QGP using a novel multi-component Chapman-Enskog framework assuming full thermalization. The approach incorporates species-specific contributions from gluons and (anti-)quarks into the plasma shear viscosity, temperature-dependent running parameters for the Debye mass and strong coupling, and a time-dependent cooling model. Our findings show that both and are enhanced by the inclusion of (anti-)quarks with gluons, and the parameters decrease over time due to the cooling and expansion of the QGP. These results align with perturbative QCD predictions, offering a more optimistic representation of QGP transport properties under dynamic conditions. This multi-component framework is compared with a multi-phase transport model that treats the QGP as a gluon gas with (anti-)quark augmentation.
... It proposes a progression from a high-density, high-temperature state, where the universe underwent successive phase transitions. The scientific community constructed heavy-ion colliders to scrutinize the Quantum Chromodynamic (QCD) phase transition, facilitating controlled experiments that emulate the primordial Big Bang conditions, often called the "mini bang" [2][3][4]. Figure 1 illustrates the envisioned phases of the quark and gluon-rich medium based on QCD [5]. The QCD phase diagram, introduced in 1975 [6], consists of two major regions: one representing the confining state where quarks and gluons are bound within hadrons and another representing the deconfined state where quarks and gluons move freely beyond hadronic boundaries. ...
This review explores the current understanding of collective excitations and the dynamics of heavy quark propagation in the quark-gluon plasma (QGP) formed in relativistic heavy-ion collisions. We focus on three core aspects: the theoretical modelling of the QGP, including momentum anisotropy, medium-induced collisions, finite chemical potential, and non-ideal interactions; the collective behaviours within the plasma; and the interaction dynamics of heavy quarks as they traverse the medium. Along with the polarization energy loss mechanisms, we also review the possibility of energy gain due to thermal field fluctuations. Lastly, we discuss how these theoretical insights can be tested through experiments and outline possible directions for future research.
... Heavy ion collisions at ultra-relativistic speeds were first proposed to provide the experimental conditions necessary to create and study the quark-gluon plasma (QGP), a novel phase of matter predicted by the completion of the standard model of physics in which quarks and gluons are deconfined throughout an extended volume [1]. Correspondingly, QGP signals were observed with the first data from collisions at the Relativistic Heavy Ion Collider (RHIC) [2][3][4][5] and then the Large Hadron Collider (LHC) [6][7][8]. The study of QGP formation, properties, evolution, and hadronization, has remained the central motivation of ultra-relativistic heavy ion collision research for the past quarter century. ...
Jets clustered from heavy ion collision measurements combine a dense background of particles with those actually resulting from a hard partonic scattering. The background contribution to jet transverse momentum () may be corrected by subtracting the collision average background; however, the background inhomogeneity limits the resolution of this correction. Many recent studies have embedded jets into heavy ion backgrounds and demonstrated a markedly improved background correction is achievable by using neural networks (NNs) trained with aspects of jet substructure which are used to map measured jet to the embedded truth jet . However, jet quenching in heavy ion collisions modifies jet substructure, and correspondingly biases the NNs' background corrections. This study investigates those biases by using simulations of jet quenching in central Au+Au collisions at with hydrodynamically modeled quark-gluon plasma (QGP) evolution. To demonstrate the magnitude of the effect of such biases in measurement, a leading jet nuclear modification factor () is calculated and reported using the NN background correction on jets quenched utilizing a brick of QGP.
... The observed collective behaviour of the produced particles in pp [1], p-Pb [2], and Pb-Pb [3] collisions at the Large Hadron Collider through measurements of two-and multi-particle azimuthal correlations is extensively studied to characterize the properties of the medium created in such collisions. While measurements of the harmonic coefficients in a Fourier decomposition of the azimuthal distribution of particles [4] compared with hydrodynamic models have revealed that the quark-gluon plasma created in heavy-ion collisions is the most perfect fluid, the origin of the collective effects in small collision systems still needs to be understood. ...
... The primary incentive for investigating high-energy heavy-ion collisions is to explore quantum chromodynamics (QCD) within environments characterized by exceptionally elevated temperatures and energy densities [1]. The experiments at super proton synchrotron (SPS) [2][3][4][5][6][7][8][9][10][11][12][13][14], at the relativistic heavy-ion collider (RHIC) [1,[15][16][17] and at the Large Hadron Collider (LHC) [18][19][20][21][22][23][24][25][26][27] are all capable of examining QCD predictions concerning the nuclear matter that is created in ultra-relativistic nucleus-nucleus (AA) collisions. High temperatures and high-energy densities lead to the liberation of tightly bound nuclear matter into quark-gluon plasma (QGP), allowing quarks and gluons to move freely, because of their increased freedom [1,3,18,28]. ...
In the present paper, we have reported the production of mesons in different centrality classes within the transverse momentum range of for Au–Au and for Cu–Cu collision. This analysis considers the mid-rapidity region of and the collision energies of 62.4 and . We have also calculated the nuclear modification factor (central to peripheral) for , mesons and baryon at different energies. For the production of mesons, we have used PYTHIA 8.3 Monte-Carlo simulation code including the color reconnection modes, CR mode 1 and CR mode 2 of PYTHIA. We have compared the resulting simulated data with experimental data from Solenoid tracker at RHIC experiment. In comparison with the PYTHIA8 and CR1 mode yields, PYTHIA CR2 mode gives good estimate of STAR data for mesons production across various centrality classes. There is a good estimate between PYTHIA CR2 and STAR data for high centrality classes while default PYTHIA8 predictions deviate more from STAR data as the centrality increases. The behavior of the nuclear modification factor, , for the meson at both and is well explained by the CR2 mode. The default PYTHIA8 predictions for meson for are fairly in close agreement to the STAR data. The ratio of strange to non-strange particles (/) is also predicted by PYTHIA model for Cu–Cu and Au–Au collisions at RHIC energies. Furthermore, an assessment for the relative abundance of considered mesons is also performed across Cu–Cu and Au–Au collisions.
... The primary objective of heavy ion collider experiments, such as the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) and the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN), is to create a small volume of matter and heat it to extreme temperatures to achieve the deconfinement of quarks and gluons. Lattice Quantum Chromodynamics (QCD) indicated that the crossover transition of strongly interacting matter [1,2,3,4,5] The ultra-relativistic heavy ion collision experiments conducted at RHIC and LHC provide crucial insights into the behavior of Quark-Gluon Plasma (QGP), demonstrating that it behaves like a perfect fluid rather than a non-interacting gas of heavy quarks and anti-quarks [7,8,10,11,12]. Experimental observations indicate that quarkonium suppression offers compelling evidence for the formation of QGP during heavy ion collisions [8,9,10,11,12,13]. This suppression highlights the plasma characteristics of the medium, including phenomena such as color screening [14], Landau damping [15], and energy loss [16]. ...
In this article, we have studied the dissociation temperature of 1S and 2S states of heavy quarkonium in the presence of anisotropy and a strong magnetic field background using the dissociation energy criterion. We utilized the medium-modified form of the Cornell potential, which depends on temperature as well as the anisotropic parameter {\xi} and the magnetic field. The binding energy (B.E.) and dissociation energy (D.E.) of heavy quarkonium have been examined for different values of the magnetic field and anisotropy. It is noted that B.E. starts decreasing from higher values as we increase the anisotropy, while D.E. exhibits the opposite behavior. The dissociation temperature appears to increase with anisotropy, while it decreases with the magnetic field, as shown in Table 1 and 2 respectively. These results align well with recent research findings.
