Probing initial geometry through collectivity in d+Au and O+O collisions at STAR
Zaining Wang (for STAR Collaboration)
A small system geometry scan provides critical insights into the initial conditions of quark-gluon plasma. The initial state conditions, influenced by structural effects such as the many-body properties of light nuclear shapes, also leave a distinct footprint in the...
Understanding the nuclear structure in heavy-ion collisions is essential, as it critically influences final state observables. However, characterizing the structure of heavy nuclei in high-energy collisions remains challenging. Current simulation methods for modeling final state events based on initial state data are highly reliant on model parameters, requiring extensive tuning and...
The Boltzmann Equation in Diffusion Approximation (BEDA) can be used as a tool for exploring the thermalization/hydrodynamization of the quark-gluon plasma. In this talk, we address this issue extending the parametric estimates obtained for small coupling in the so-called bottom-up thermalization by Baier, Mueller, Shiff and Son by introducing quarks and antiquarks in the calculation. Then, we...
Weakly coupled QCD kinetic theory can well describe the non-equilibrium evolution of the Quark-Gluon Plasma in the early stages of high-energy nuclear collisions. Previous studies in homogeneous and boost invariant systems have shown rapid hydrodynamisation and entropy production during the first 1 fm/c. In this work, we relax the assumption of boost invariance and study the early time...
Dibaryons, exotic states composed of six quarks, have long been a subject of interest in understanding the strong interaction beyond conventional hadrons. Among these, strange dibaryons, which contain strange quarks, offer an important role of studying the hyperon-nucleon ($YN$) and hyperon-hyperon ($YY$) interactions . Of particular interest are the spin-0 $H$ ($S$ = -2) and the spin-2...
Hypernuclei are bound states formed between nucleons and hyperons. The measurement of their production in high-energy hadronic collisions provides a powerful probe for investigating the interaction forces that bind strange baryons to ordinary nucleons and for testing nucleosynthesis models. Among the light hypernuclei, the possible existance of the $\Lambda$-n-n remains an open question. After...
The study of exotic resonances provides insights into the non-perturbative regime of Quantum Chromodynamics (QCD). Short-lived resonances such as ( f_0(980) ), ( f_1(1285) ), and ( f_2(1270) ) have been extensively investigated to explore their internal structures, which remain uncertain with possibilities including tetraquark states or meson-meson molecular states. Among them, the (...
The study of exotic hadrons has long been a topic of great interest for the understanding of Quantum Chromodynamics (QCD). As one of the light exotic hadrons, the structure and constituent quark content of $f_0(980)$ have been debated for decades, with theories suggesting it could be a tetraquark state ($s\bar sq\bar q$) or a hadronic molecule ($K\bar K$). Recently, the CMS experiment has...
QCD equation of state (EoS) characterizes the equilibrium properties of strongly interacting hot and dense matter. External factors, especially strong magnetic fields reaching magnitudes comparable to the QCD scale, can significantly influence this characterization. Of particular interest is how such strong magnetic fields affect the changes in degrees of freedom and thermodynamic properties...
We investigate the thermodynamics of a quark-meson plasma under external magnetic field in frame of a two-flavor Nambu-Jona-Lasinio (NJL) model. We calculate the thermodynamic functions and the chiral restoration phase transition to order 1 /Nc in an expansion in the inverse number of colours, which is seen to include mesonic exchange. We discuss the magnetic field effect on the bound and...
Neutral and charged vector mesons can be sensitive to isospin-violating effects induced by Landau level splitting in the presence of a strong
magnetic field ($B$) within a QCD medium~\cite{meson_spiltting_njl}. One such example is the neutral $K^{*0}$ ($d\bar{s}$) and the charged $K^{*+}$ ($u\bar{s}$), which have similar masses and isospin. However, the magnetic moments of their constituent...
The observation of hyperon global polarization along the system's angular momentum has revealed the existence of large vorticities in the medium created by heavy-ion collisions.
Using the high-statistics data collected by the STAR experiment during the RHIC Beam Energy Scan II (BES-II) program with upgraded detector systems, we present the global polarization measurements for $\Lambda$,...
The observation of hyperon polarization along beam direction ($P_z$) in nucleus-nucleus collisions has opened a new way to study the complex vortical structures of the QGP. With the high-statistics data collected by the CMS experiment, we present the first $P_z$ results for $\Lambda$ and $\bar{\Lambda}$ particles in pPb collision at $\sqrt{s_{NN}}= 8.16$ TeV over a wide transverse momentum...
In High-Energy Heavy-Ion Collisions, the anisotropic flow is expected to be directly related to the shear viscosity coefficient. However, it has been known [1] that there is a sizeable modeling uncertainty in the non-equilibrium correction for the Cooper-Frye prescription in multi-stage modeling of heavy-ion collisions, which strongly impacts particle-number-based final-state observables....
Shear and bulk viscosities are two key transport coefficients that characterize the fundamental properties of quark-gluon plasma. They quantify the response of the energy-momentum tensor to the shear flow and divergent flow, serving as crucial input parameters for the phenomenological and transport models that interpret experimental data, e.g. the elliptic flow $v_2$.
However, calculating...
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Significant efforts have been made within the heavy-ion collision community to locate the QCD critical endpoint (CEP). Recent lattice QCD studies using imaginary chemical potentials, based on simulations at temperatures above 120 MeV and utilizing Lee-Yang edge singularities in the complex chemical potential plane, suggest that the critical temperature at the CEP, $T_c^{CEP}$,...
We present the first lattice QCD results of quadratic fluctuations and correlations of conserved charges in (2+1)-flavor lattice QCD in the presence of a background magnetic field. The simulations were performed using the Highly Improved Staggered Quarks with physical pion mass $m_\pi$ = 135 MeV on $N_\tau=8$ and 12 lattices. We find that the correlation between net baryon number and electric...
The STAR experiment collected large-statistics datasets from isobar collisions of $^{96}_{44}\text{Ru}+^{96}_{44}\text{Ru}$ and $^{96}_{40}\text{Zr}+^{96}_{40}\text{Zr}$ ions, offering a valuable opportunity to study Coulomb dissociation via Ultra-peripheral collisions (UPC). Despite having identical mass numbers, these isobars exhibit distinct proton and neutron distributions, leading to...
Relativistic heavy-ion collisions offer a unique environment for exploring quantum interference at an unprecedented femtometer scale through photon-nuclear interactions in photoproduction. In exclusive $\pi^{+}\pi^{-}$ production, the resonance and continuum $\pi^{+}\pi^{-}$ components arise from distinct production mechanisms in the $\gamma {\rm A}$ interaction. The continuum $\pi^{+}\pi^{-}$...
The measurement of the magnetic field created in high-energy heavy-ion collisions is challenging, due to the fact that the magnetic field decays so drastically that in a thermalized quark-gluon plasma the field strength becomes rather weak. By incorporating the weak magnetic effect into the medium, and especially into the production formalism of dileptons from the quark-gluon plasma, the...
A jet is a spray of collimated hadrons originating from the fragmentation of an energetic parton. In heavy-ion collisions, jets traverse the colored medium and lose energy via induced gluon radiation and elastic scattering, which modify jet yields and structure. When the overlap of the colliding nuclei is small, the transverse profile of the quark-gluon plasma (QGP) is expected to become more...
High-multiplicity (HM) final states of small collision systems exhibit collective phenomena which resemble the well-established signatures of the quark--gluon plasma (QGP) formed in heavy-ion collisions. However, jet quenching has not been observed in small collision systems. Quantification or setting limits on the magnitude of jet quenching in small collision systems is crucial for...
In proton-proton ($pp$) collisions, hard-scattered partons will undergo perturbative fragmentation and hadronization, resulting in a collimated collection of hadrons that can be measured as a jet. The N-Point Energy correlator (ENC) is a jet substructure observable formed out of the distribution of angular distances between all particle groups of N constituents in a jet weighted by their...
In relativistic heavy-ion collisions, a hot and dense QCD medium, known as the Quark-Gluon Plasma, is formed. Simultaneously, hard-scattered partons from these collisions interact with the medium, leading to the production of particle cascades called jets. These jets are modified as they traverse the QGP, a phenomenon referred to as jet quenching. Various jet observables, including jet mass...
Recent experimental results on two-particle correlations within jets in high multiplicity pp collisions highlight a strong flow-like correlation among constituents.
This has brought to the hypothesis of a formation of a hot and dense QCD medium within those jets. This observation suggests new insights of particle interaction dynamics in pp collisions, previously thought to be exclusive to...
Early Thermalization in kenitic theory via spectrum method: The Role of Pair-Correlations
Relativistic hydrodynamics has provided an excellent description of the Quark-Gluon Plasma (QGP) produced in heavy-ion collisions. However, as a framework for describing collective behaviors in many-body systems at the...
High-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions at the LHC have revealed that even smaller collision systems show the onset of phenomena typical of heavy-ion collisions. Strangeness enhancement and collective flow, two examples of such phenomena, suggest that light-flavor hadron production arises from complex mechanisms of which relative contributions evolve smoothly...
The study of strange hadrons plays a critical role in understanding the properties of hot and dense nuclear matter created in heavy-ion collisions, as they provide unique insights into the quantum chromodynamics phase transition and the possible formation of a quark-gluon plasma. Strangeness enhancement, first proposed as a signature of quark-gluon plasma, arises from the high production rate...
Production of light nuclei in Au+Au collisions with the STAR BES-II program
Liubing Chen(for the STAR Collaboration)
Central China Normal University
The studies of the production of light nuclei, such as deuteron, triton, and helium nuclei in heavy-ion collisions, are essential for understanding the dynamics of nuclear matter under extreme conditions and provide valuable insights into...
The measurements of the production of charm quarks at the LHC have provided an essential ingredient for understanding their hadronization mechanism in hadronic collisions.
The observation of enhanced charm-baryon production compared to meson production has led to a reconsideration of the assumption on the universality of the fragmentation process across different collisions systems, which...
Measurements of the production of heavy-flavour hadrons in proton–proton (pp) collisions provide an important test of quantum chromodynamics (QCD). The heavy-flavour production cross section can be calculated using the factorisation approach as a convolution of three factors: the parton distribution functions (PDFs), the partonic cross section calculated with perturbative QCD calculations, and...
Strange Charm-Meson Production in pp Collisions at $\sqrt{s} = 13.6$ TeV with ALICE
Precise measurements of charm-strange hadron production play a critical role in testing perturbative QCD calculations based on the factorization approach. Moreover, comparing the production yields of strange relative to that of non-strange charm hadrons in different colliding systems provides essential...
sPHENIX is a cutting-edge experiment at the Relativistic Heavy Ion Collider (RHIC), focused on heavy-flavor and jet physics. Its design enables high-precision measurements in 200 GeV p+p and Au+Au collisions. The sPHENIX tracking system includes the Monolithic Active Pixel Sensor-based Vertex Detector (MVTX), Intermediate Silicon Tracker (INTT), Time Projection Chamber (TPC), and TPC outer...
In recently years, the real-time evolution based on the Hamiltonian formulation of the lattice gauge theories has been investigated to challenge the so-called sign problem which is the inefficient sampling issue of the quantum Monte Carlo method when we have topological terms, chemical potentials or real time. Thanks to the recent rapidly developed quantum computing technology, it is...
Quarkonium production can be used to probe the matter formed in ultrarelativistic heavy-ion collisions. However, for theoretical understanding of the experimental results on quarkonium production in heavy-ion collisions it is necessary to know if and which quarkonium states exist above the crossover temperature, $T_c$ and what are the in-medium masses and widths of different quarkonium states....
Quarkonia are a valuable tool to investigate strongly interacting medium under extreme conditions, and particularly Quark Gluon Plasma (QGP). In heavy ion collisions, heavy quarks are produced in the early stages of the collisions and thus they experience the whole QGP evolution, allowing to investigate its properties. In addition, at LHC energies, (re)generation process has been found to have...
Multiple Parton Interactions (MPI) play a crucial role in hadron-hadron collisions, contributing to the complexity of the final state in high-energy physics experiments. In these interactions, multiple partons from each hadron can simultaneously interact within a single collision event. Among the various MPI scenarios, Double-Parton Scattering (DPS) is the simplest form, where two distinct...
Quarkonium production in high-energy lead-lead (Pb-Pb) collisions is a key tool for exploring both the perturbative and non-perturbative aspects of quantum chromodynamics (QCD) calculations.
Charmonia are bound states consisting of a charm and an anti-charm quark. Their production process can be divided into two stages: the creation of the heavy quarks and the formation of the bound state....
Quarkonium production has long served as a probe for heavy quark interaction with nuclear medium. In small collision systems, quarkonia can be modified by initial state effects like shadowing, and final state effect like interacting with co-moving particles. The possible signature due to potentially existing deconfined medium (Quark Gluon Plasma) need to be disentangled from all aforementioned...
The $J/\psi$ meson, consisting of a charm quark and its antiquark, serves as an exceptional testing ground of Quantum Chromodynamics (QCD). However, our understanding of its underlying production mechanism remains incomplete. One of the principal challenges lies in experimentally disentangling perturbative from non-perturbative process contributions. The recently proposed $J/\psi$-energy...
As recently observed by the STAR and ALICE collaborations, the global and local
spin polarization of $\Lambda$-hyperons provides new insights into spin dynamics
in heavy-ion collisions. There are various contributing factors that could be the
source of hyperon polarization. However, among them, the vorticity field is widely
considered as the primary source of particle polarization in...
We present a measurement of $\Upsilon$ polarization in PbPb collisions with the CMS detector. The results are obtained in the helicity and Collins-Soper frames and compared with the corresponding measurements in pp collisions. Until now, all studies of quarkonium suppression in heavy ion collisions have assumed unpolarized production in the computation of the detection acceptance. The observed...
