One of the main physics goals of the Beam Energy Scan (BES) program at RHIC is to study the QCD phase diagram, especially around the phase transition between the quark-gluon plasma (QGP) and hadronic matter. BES Phase-I studied Au+Au collisions from center-of-mass energy ($\sqrt{s_{_{\rm{NN}}}} $) of 7.7 to 62.4 GeV. BES Phase-II extended these measurements in several important ways, one of...
Constituent quark number scaling has been proposed as one of the key signatures of a QGP phase. The flow scaling arises from a quark coalescence picture relevant at intermediate transverse momenta. While at collision energies above 7.7 GeV the NCQ scaled elliptic flow of baryons and mesons aligns very well, the scaling breaks between 4.5 and 3.0 GeV as evidenced by recent STAR measurements. At...
Collective phenomena and the baryon-to-meson ratio in high-energy nuclear collisions provide unique insights into the formation and evolution of the quark--gluon plasma (QGP). For the first time, elliptic ($v_2$) and triangular ($v_3$) flow coefficients of strange hadrons ($\Lambda$ and $K^{0}_{S}$), together with $\Lambda/K^{0}_{S}$ ratios, are measured in light-ion (OO and NeNe) collisions...
Most current initial condition models for ultra-relativistic heavy-ion collisions assume an
initial state based on gluon saturation, such as IP-Glasma and EKRT. However, conventional hydrodynamics models rely on an assumption of chemical equilibrium between quarks and gluons, even though the timescales of equilibration remain an open question. Here we test this equilibrium assumption, using...
Thermal dielectrons serve as an ideal thermometer to probe the average temperature of the hot and dense QCD medium created in heavy-ion collisions. Previous measurements over a wide range of collision energies and collision systems exhibit consistent temperature trends, indicating significant contributions from the quark-gluon plasma (QGP). Oxygen-oxygen (O+O) collisions, with an effective...
Radial and anisotropic flow are key observables for probing the expansion dynamics of the quark-gluon plasma (QGP). The first measurement of transverse momentum–dependent radial flow fluctuations, v0(pT), in Pb+Pb collisions is presented. The $v_0(p_T)$ observable exhibits three key features: (i) long-range correlations in pseudorapidity, (ii) factorization in $p_T$, and (iii) a...
Understanding the expansion dynamics and transport properties of the quark--gluon plasma (QGP) is one of the central goals of heavy-ion collision experiments. The newly proposed observable $v_0(p_T)$ [1], which is directly sensitive to $p_T$-differential fluctuations of radial flow, has been measured by the LHC experiments [2,3] and has been suggested as a sensitive probe of the medium's bulk...
We present, for the first time, the charmed hadron $p_T$–differential radial flow $v_0(p_T)$, within a Langevin transport framework that incorporates event-by-event fluctuations. We propose $v_0(p_T)$ of heavy quarks as a novel and sensitive observable for probing the properties of the Quark–Gluon Plasma (QGP). This observable exhibits a pronounced sensitivity to the interaction strength...
We present recent STAR measurements of the newly proposed radial flow fluctuation coefficient, $v_{0}(p_{T})$, for strange and multi-strange hadrons in heavy-ion collisions at RHIC. The $v_{0}(p_{T})$ of strange and multi-strange hadrons is of great interest because these particles are less affected by late-stage hadronic interactions, making them good probes of the early partonic stage. The...
In heavy-ion collisions, azimuthal correlations probe collective phenomena in the hot and dense medium formed, known as the Quark–Gluon Plasma (QGP). In small collision systems, similar correlations may arise from final-state effects or from initial-state parton correlations. The LHCb experiment has a unique capability to study particle correlations in high-energy hadron collisions at forward...
Charm quarks, produced in the earliest stages of high-energy heavy-ion collisions due to their large masses, are sensitive to the full evolution of the strongly interacting medium and serve as unique probes of its collective properties. Measuring the elliptic flow ($v_{2}$) of open-charm hadrons across different collision systems provides crucial insight into the onset and strength of...
Heavy quarks serve as pristine probes of the transport properties and hadronization dynamics of the quark–gluon plasma (QGP) created in high-energy nuclear collisions. A key challenge in this context is to embed the interactions of heavy quarks in the expanding medium compatible with the strong-coupling nature of the QGP, and thus to unravel the underlying microscopic mechanisms. Toward this...
The dynamics of heavy quarks in quark-gluon plasma (QGP) formed in heavy ion collisions provide a unique window to characterize its properties. Existing approaches to describe heavy quarks in medium rely either on quasiparticle-based models of QGP, or on assuming that the momentum transfer from the medium follows Gaussian statistics. However, neither of these assumptions can be taken for...
The charm quark is formed almost exclusively during the initial stages of the collision, and a significant fraction of the charm quarks fragment into the $D^{0}$ meson, the lightest open-charm hadron. We can gain insights into the interactions between the charm quark and the quark-gluon plasma (QGP) medium by studying the production and the flow of $D^{0}$ mesons in heavy-ion collisions. We...
We derive the leading modifications to transverse momentum broadening and medium-induced gluon spectrum in flowing matter for the case of a heavy flavor quark. We show that the broadening and radiation patterns acquire a new directional dependence arising from the interplay between the quark mass and the medium flow — an effect absent in the massless case. Consequently, the dead-cone effect is...
Heavy-flavour production represents a crucial probe for studying transport properties of the Quark-Gluon Plasma (QGP), with the spatial diffusion coefficient $D_s(T)$ encoding the interaction strength between heavy quarks (HQs) and the medium. Recent lattice QCD (lQCD) results with dynamical fermions show very low values, $2\pi T D_s \approx 1$ for charm quarks at $T = T_c$, much lower than...
The suppression of quarkonium production in heavy-ion collisions has long been recognized as a key signature of QGP formation, reflecting the medium’s temperature and color-screening properties. However, interpreting the observed nuclear modification factor ($R_{AA}$) remains challenging due to the interplay between hot-medium effects (dissociation and regeneration) and cold nuclear matter...
The charm quark serves as a powerful probe for investigating the properties of the hot and dense QCD medium, the quark-gluon plasma (QGP), created in high-energy heavy-ion collisions. Building on previous studies that demonstrated the applicability of a fluid-dynamic description of charm quarks in the quark-gluon plasma, the present work (https://arxiv.org/abs/2510.25601) extends this...
Recent results from the LHC on oxygen–oxygen (O-O) and xenon–xenon (Xe-Xe) collisions open a new window for investigating the interplay of cold nuclear matter (CNM) and quark–gluon plasma (QGP) effects in small collision systems. Building upon recent theoretical work on particle production dynamics in heavy ion reactions, we present an updated study of light and heavy hadron modification...
Energetic collisions of heavy nuclei have long been known to create a hot and dense state of matter known as the quark-gluon plasma (QGP). The QGP may also be created in collisions of heavy-on-light and even light-on-light nuclear collisions. One key signature of QGP formation is the development of long-range angular correlations, which indicate the propagation of early-time position-space...
