Centrality Dependence Research Articles

Strangeness production in sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 3 GeV Au+Au collisions at RHIC

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 3 GeV with the STAR experiment at RHIC. KS0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {K}_S^0 $$\\end{document} meson and Λ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of Λ and KS0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {K}_S^0 $$\\end{document} are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4π yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

Magnetic field effect on hadron yield ratios and fluctuations in a hadron resonance gas

This work studies the influence of an external magnetic field on hadron yields and fluctuations in a hadron resonance gas by performing calculations within an updated version of the open-source package. The presence of the magnetic field has a sizable influence on certain hadron yield ratios. Most notably, it leads to enhanced p/π and suppressed n/p ratios, which may serve as a magnetometer in heavy-ion collisions. By attributing the centrality dependence of the p/π ratio in Pb-Pb collisions at 5.02 TeV measured by the ALICE Collaboration entirely to the magnetic field, its maximal strength at freezeout is estimated to be eB≃0.12GeV2≃6.3mπ2 in peripheral collisions. The magnetic field also enhances various conserved charge susceptibilities, which is qualitatively consistent with recent lattice QCD data and is driven in the HRG model by the increase of hadron densities. However, the variances of hadrons do not show any enhancement when normalized by the means, therefore, measurements of second-order fluctuations in heavy-ion collisions appear to offer limited additional information about the magnetic field relative to mean multiplicities. Published by the American Physical Society 2024

Probing the internal structures of pΩ and ΩΩ with their production at the Large Hadron Collider

The strange dibaryons pΩ (S25) and ΩΩ (S01) are likely bound, existing either in molecular states like the deuteron or as more exotic compact six-quark states. Here, we investigate the production of these two dibaryons in Pb+Pb collisions at sNN=2.76 TeV at the CERN Large Hadron Collider within a covariant coalescence model, which employs a blast-wave-like parametrization for the phase-space configurations of constituent particles at freeze-out. For the molecular states, the pΩ and ΩΩ are produced via p−Ω and Ω−Ω coalescence, respectively, while for the six-quark states, they are formed through uudsss and ssssss coalescence. We find that the yield ratios NpΩ/NΩ and NΩΩ/NΩ have a distinct centrality dependence between the molecular and multiquark states, thus offering a promising way for distinguishing the two states. Our results suggest that the measurements of pΩ and ΩΩ production in relativistic heavy-ion collisions can shed light on their internal structures. Published by the American Physical Society 2024

Medium-assisted enhancement of χc1(3872) production from small to large colliding systems

Studies of exotic hadrons such as the χc1(3872) state provide crucial insights into the fundamental force governing the strong interaction dynamics, with an emerging frontier to investigate their production in high energy collisions where a partonic medium is present. The latest experimental measurements from the Large Hadron Collider show an intriguing evolution pattern of the χc1(3872)-to-ψ(2S) yield ratio from proton-proton collisions with increasing multiplicities toward proton-lead and lead-lead collisions. Here we propose a mechanism of medium-assisted enhancement for the χc1(3872) production, which competes with the more conventional absorption-induced suppression and results in a nonmonotonic trend from small to large colliding systems. Realistic simulations from this model offer a quantitative description of all available data. Predictions are made for the centrality dependence of this observable in PbPb collisions as well as for its system-size dependence from OO and ArAr to XeXe and PbPb collisions. In both cases, a nonmonotonic behavior emerges as the imprint of the competition between enhancement and suppression and can be readily tested by future data. Published by the American Physical Society 2024

Bottom quark dynamics from nonprompt D0 and J/ψ production in Pb+Pb collisions at sNN=5.02 TeV

We study bottom quark energy loss via the nuclear modification factor (RAA) and elliptic flow (v2) of nonprompt D0 and J/ψ in relativistic heavy-ion collisions at the Large Hadron Collider (LHC). The space-time profile of quark-gluon plasma is obtained from the hydrodynamics simulation, the dynamical evolution of heavy quarks inside the color deconfined QCD medium is simulated using a linear Boltzmann transport model that combines Yukawa and string potentials of heavy-quark-medium interactions, the hadronization of heavy quarks is performed using a hybrid coalescence-fragmentation model, and the decay of B mesons is simulated via . Using this numerical framework, we calculate the transverse momentum (pT) dependent RAA and v2 of direct D mesons, B mesons, and nonprompt D0 and J/ψ from B meson decay in Pb+Pb collisions at sNN=5.02 TeV. We find the mass hierarchy of the nuclear modification of prompt D and B mesons depends on their pT. Both RAA and v2 of heavy flavor particles show strong pT and centrality dependences due to the interplay between parton energy loss, medium geometry and flow, and hadronization of heavy quarks. Nonprompt D0 and J/ψ share similar patterns of RAA and v2 to B mesons except for a pT shift during the decay processes. Therefore, future more precise measurements on nonprompt D0 and J/ψ can help further pin down the bottom quark dynamics inside the quark-gluon plasma. Published by the American Physical Society 2024

Strongly intensive pseudo-rapidity fluctuation in event-by-event basis: an outlook to centrality dependence

Strongly intensive pseudo-rapidity fluctuation in event-by-event basis: an outlook to centrality dependence

Centrality dependence of multistrange baryon production in high-energy heavy-ion collisions

We consider the experimental data on the production of strange \Lambda^{\prime}Λ′s, and multistrange baryons (\XiΞ, \OmegaΩ), and antibaryons, on nuclear targets, at the energy region from SPS up to LHC, in the framework of the Quark-Gluon String Model. One remarkable result of this analysis is the significant dependence on the centrality of the collision of the experimental \overline{\Xi}^+/\overline{\Lambda}Ξ¯+/Λ¯ and \overline{\Omega}^+/\overline{\Lambda}Ω¯+/Λ¯ ratios in heavy-ion collisions, at SPS energies.

Examining the influence of hadronic interactions on the directed flow of identified particles in RHIC Beam Energy Scan energies using UrQMD model

The directed flow of identified particles can serve as a sensitive tool for investigating the interactions during initial and final states in heavy ion collisions. This study examines the rapidity distribution ([Formula: see text]), rapidity-odd directed flow ([Formula: see text]) and its slope ([Formula: see text]) for [Formula: see text], [Formula: see text], p, and [Formula: see text] in Au+Au collisions at different collision centralities and beam energies ([Formula: see text], 11.5, 14.5, 19.6, 27, and 39[Formula: see text]GeV) using the UrQMD model. We investigate the impact of late-stage hadronic interactions on charge-dependent [Formula: see text] and its slope by modifying the duration of the hadronic cascade lifetime ([Formula: see text]). The energy dependence of [Formula: see text] for p ([Formula: see text]) exhibits distinct pattern compared to [Formula: see text] and [Formula: see text]. Notably, we observe a change in the sign reversal position of proton [Formula: see text] at different beam energies with varying [Formula: see text] in central and mid-central collisions. Moreover, the difference in [Formula: see text] between positively and negatively charged hadrons ([Formula: see text]) demonstrates a stark centrality dependence for different particle species. The deuteron displays a significant increase in [Formula: see text] with increasing [Formula: see text] compared to p and n. This investigation underscores the importance of considering the temporal evolution and duration of the hadronic phase when interpreting the sign reversal, charge splitting of [Formula: see text] and light nuclei formation at lower RHIC energies.

Measurement of the Centrality Dependence of the Dijet Yield in p+Pb Collisions at sqrt[s_{NN}]=8.16 TeV with the ATLAS Detector.

ATLAS measured the centrality dependence of the dijet yield using 165 nb^{-1} of p+Pb data collected at sqrt[s_{NN}]=8.16 TeV in 2016. The event centrality, which reflects the p+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, R_{CP}, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The R_{CP} shows a scaling with the Bjorken x of the parton originating from the proton, x_{p}, while no such trend is observed as a function of x_{Pb}. This analysis provides unique input to understanding the role of small proton spatial configurations in p+Pb collisions by covering parton momentum fractions from the valence region down to x_{p}∼10^{-3} and x_{Pb}∼4×10^{-4}.

Beam energy and system size dependence of heavy flavor production at STAR

We report the measurements of quarkonia (J/ψ and ψ(2S)) in heavyion collisions via the e+e− decay channel at midrapidity (|y| < 1) by the STAR experiment. The centrality and transverse momentum dependence of the yield ratio of ψ(2S) to J/ψ is measured for the first time in heavy-ion collisions at RHIC. These results, together with the new measurement of collision energy dependence of inclusive J/ψ suppression in Au+Au collisions, allow for a systematic study of the quarkonium production in the medium. In addition, we present the first measurement of J/ψ polarization in heavy-ion collisions at RHIC in both the Helicity and the Collins-Soper frames, which provides a new insight for studying the properties of the Quark-Gluon Plasma created in heavy-ion collisions.

Elliptic and triangular flow of light nuclei in Au+Au collisions in the BES-II energies using the STAR detector

Light nuclei might be formed in heavy-ion collisions by the coalescence of produced (anti-)nucleons or transported nucleons. Due to their low binding energies, they are more likely to form at later stages of the hadronic fireball. In this proceedings, we report the transverse momentum and centrality dependence of elliptic (v2) and triangular (v3) flow of d, t, and 3He in Au+Au collisions at √SNN = 14.6 - 54.4 GeV. The mass number scaling of v2(pT) and v3(pT) of light nuclei is discussed. We also report the comparison of v2(pT) and v3(pT) of light nuclei with a transport-plus-coalescence model calculation.

Hypertriton production in Au+Au collisions from STAR BES-II

Hypernuclei are bound states of nuclei with one or more hyperons. Precise measurements of hypernuclei properties and their production yields in heavy-ion collisions are crucial for the understanding of their production mechanisms. The second phase of the Beam Energy Scan at RHIC (BES-II) offers us a great opportunity to investigate collision energy and system size dependence of hypernuclei production. In these proceedings, we present new measurements on transverse momentum (pT), rapidity (y), and centrality dependence of Λ3H production yields in Au+Au collisions from √SNN = 3 to 27 GeV. These results are compared with phenomenological model calculations, and physics implications on the hypernuclei production mechanism are also discussed.

Probing initial state effects in nuclear collisions via jet and top-quark measurements with the ATLAS detector

Proton-lead collisions at the Large Hadron Collider energies offer a unique possibility to investigate initial state effects in nuclear collisions. Thanks to its wide acceptance, ATLAS can measure several probes that can help characterise these effects over a wide kinematic range. By analyzing the centrality dependence of dijet production, it is possible to investigate the suppression of dijet events in central collisions compared to peripheral ones and correlate it to the kinematic of the parton-parton scattering, accessible via the measurement of both jets in the final state. Also, the first measurement of the inclusive crosssection for top-quark pair production in dilepton and lepton+jet decay modes is reported. This process is sensitive to effects at high Bjorken-x values, which are hard to access experimentally using other available probes, and thus provides complementary information on the behavior of nuclear parton densities. In 2016, the ATLAS experiment collected 165 nb−1 of proton-lead collisions at a center-of-mass energy of 8.16 TeV per nucleon pair. In this article, new measurements of the centrality dependence of dijet production and the observation of top-quark pair production using this dataset are presented.

Anomalous kaon correlations measured in Pb-Pb collisions at the LHC as evidence for the melting and refreezing of the QCD vacuum

Measurements of the dynamical correlations between neutral and charged kaons in central Pb-Pb collisions at √SNN = 2.76 TeV by the ALICE Collaboration display anomalous behavior relative to conventional heavy-ion collision simulators. We consider other conventional statistical models, none of which can reproduce the magnitude and centrality dependence of the correlations. The data can be reproduced by coherent emission from domains which grow in number and volume with increasing centrality. We study the dynamical evolution of the strange quark condensate and show that the energy released during the expansion and cooling of the system may be sufficient to explain the anomaly.

Energy and system size dependence of strongly intensive fluctuation measures in heavy-ion collisions at FAIR energies

Event-by-event fluctuations of multiplicity and transverse momentum of charged hadrons produced in heavy-ion collisions at FAIR energies, 10A, 20A, 30A, and 40A GeV are studied in the framework of relativistic transport model, URQMD. Dependence of two families of strongly intensive measures of multiplicity(N) and transverse momentum (p T) fluctuations, Δ[p T, N] and Σ[p T, N], on collision centrality, centrality bin-widths and pseudorapidity windows are examined. Attempts are also made to study NN, N p T, and p T p T fluctuations using two window analysis method. The findings suggest that the measure, Δ[p T, N] be dealt with proper selection of centrality intervals. This measure also exhibits a strong dependence on the widths of η windows. The variable Σ[p T, N], however, is observed to be insensitive to the centrality bin-widths and shows a variation of <5% with the widths of η windows. The analysis of data after event mixing gives Δ[p T, N] and Σ[p T, N] values as ∼1 irrespective of the widths of η windows and collision centrality, as predicted by a model of independent particle emission, IPM. The study of joint fluctuations of the two quantities on two η windows separated in η space, reveals that Σ[N F, N B] values are ∼1 irrespective of the position of η windows whereas, the values of and firstly increase with η sep and later acquire saturations. The observed trend of centrality dependence of and agrees fairly well with those observed in MC simulated studies carried out for AA collisions at LHC energies in the framework model of string fusion.

Centrality and System Size Dependence among Freezeout Parameters and the Implications for EOS and QGP in High-Energy Collisions.

Utilizing the Modified Hagedorn function with embedded flow, we analyze the transverse momenta (pT) and transverse mass (mT) spectra of π+ in Au-Au, Cu-Cu, and d-Au collisions at sNN = 200 GeV across various centrality bins. Our study reveals the centrality and system size dependence of key freezeout parameters, including kinetic freezeout temperature (T0), transverse flow velocity (βT), entropy-related parameter (n), and kinetic freezeout volume (V). Specifically, T0 and n increase from central to peripheral collisions, while βT and V show the opposite trend. These parameters also exhibit system size dependence; T0 and βT are smaller in larger collision systems, whereas V is larger. Importantly, central collisions correspond to a stiffer Equation of State (EOS), characterized by larger βT and smaller T0, while peripheral collisions indicate a softer EOS. These insights are crucial for understanding the properties of Quark-Gluon Plasma (QGP) and offer valuable constraints for Quantum Chromodynamics (QCD) models at high temperatures and densities.

Elliptic flow of inclusive charged hadrons in Au+Au collisions at E lab = 35 A GeV using the PHSD model

Elliptic flow (v 2) of inclusive charged hadrons at mid-rapidity (∣η∣ < 1.0) in Au+Au collisions at E lab = 35 A GeV using the parton hadron string dynamics (PHSD) model are presented as a function of centrality, transverse momentum (p T) and pseudo-rapidity (η). The v 2 results are obtained using the η-sub event plane method with respect to the event plane angle (ψ 2) and participant plane angle (). p T-integrated charged hadron v 2 shows a strong centrality dependence in Au+Au collisions at E lab = 35 A GeV. The eccentricity-scaled elliptic flow (v 2/ε 2) also shows centrality dependence. The higher values of v 2/ε 2 in central collisions suggest the development of stronger collectivity. The calculations are compared with the results from Au+Au collisions at published by the STAR experiment at RHIC. We also compare the results of HSD and PHSD modes to investigate the contribution of hadronic and partonic phases of the medium on the calculated v 2. The current results serve as a prediction of the collective behavior of the matter produced in baryon-rich and moderate temperature conditions for the upcoming multi-purpose detector at the nuclotron-based Ion collider facility (NICA) and compressed baryonic matter experiment at the facility for antiproton and ion research. These predictions are also useful for interpreting data measured at relativistic heavy ion collider (RHIC) beam energy scan program.

Pseudo-rapidity distributions of charged particles in asymmetric collisions using Tsallis thermodynamics

The pseudo-rapidity distributions of the charged particles produced in the asymmetric collision systems p+Al, p+Au and 3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}He+Au at sNN=200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_\ ext {NN}} = 200$$\\end{document} GeV are evaluated in the framework of a fireball model with Tsallis thermodynamics. The fireball model assumes that the experimentally measured particles are produced by fireballs following the Tsallis distribution and it can effectively describe the experimental data. Our results as well as previous results for d+Au collisions at sNN=200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_\ ext {NN}} = 200$$\\end{document} GeV and p+Pb collisions at sNN=5.02\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_\ ext {NN}} = 5.02$$\\end{document} TeV validate that the fireball model based on Tsallis thermodynamics can provide a universal framework for pseudo-rapidity distribution of the charged particles produced in asymmetric collision systems. We predict the centrality dependence of the total charged particle multiplicity in the p+Al, p+Au and 3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}He+Au collisions. Additionally, the dependences of the fireball model parameters (y0a\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$y_{0a}$$\\end{document}, y0A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$y_{0A}$$\\end{document}, σa\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma _{a}$$\\end{document} and σA\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma _{A}$$\\end{document}) on the centrality and system size are studied.

Analysis of centrality dependences of pion multiplicity events using their higher moments in relativistic heavy ion collisions

In this study, data on charged-pion production in relativistic oxygen-ion collisions are examined with varying degrees of centrality. Using the multiplicity of producing charged pions, it is proved that there is a relationship between centrality degrees and collision parameters (such as the impact parameter [Formula: see text], target size fragments, [Formula: see text] and the total charge of projectile spectators, [Formula: see text]. The various order moments of the multiplicity distributions are used in the standard way to investigate the underlying correlations. The evidence suggests that all the pions produced at the various target sizes ([Formula: see text]-values) correlate. The higher moments are also investigated at various centrality classes decided by the parameter [Formula: see text]. The multiplicity fluctuations, as measured by the variance-to-mean ratio, showed that the multiplicity distributions of produced pions are not Poissonian, regardless of how they were examined using the two parameters [Formula: see text] and [Formula: see text]-values.

Elliptic flow of identified hadrons in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the PHSD model

We present predictions of elliptic flow (v_2) of identified hadrons at mid-rapidity (|y| < 1.0) in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (p_{textrm{T}}) dependence of identified hadron v_2 in minimum bias (0–80%) and three different centrality intervals (0–10%, 10–40%, and 40–80%) are presented. A clear centrality dependence of v_2(p_{textrm{T}}) is observed for particles and anti-particles. We also present the p_{textrm{T}} dependence of v_2 difference ({Delta } v_2) between particles and corresponding anti-particles. A significant difference in v_2 values for baryons and anti-baryons is observed. Constituent quark scaling (NCQ) of v_{2} is investigated in Au+Au collisions. We also present a v_2(p_{textrm{T}}) ratio between the HSD and PHSD modes to explore the effect of hadronic and partonic interactions in the medium. These predictions are useful for interpreting the data measured in the Beam Energy Scan (BES) program at RHIC. They will also be useful for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).