Search

Understanding the internal spin structure of the nucleon remains a challenge in strong interaction physics. The unique capability of RHIC opened new avenues in studying the internal structure of the proton with unprecedented depth and precision. Significant progress has been made in the last few years through various measurements at STAR. The longitudinal spin measurements have contributed significantly to our understanding of the quark and gluon helicity distributions inside the proton. The longitudinal double-spin asymmetry, ALL, from STAR inclusive jet and dijet measurements provides the first evidence of a positive gluon polarization with partonic momentum fraction x > 0.05. The reconstruction of W±/Z in longitudinally polarized proton-proton collisions indicates that there is a flavor separation of the light sea quark helicity distributions. In transversely polarized proton collisions, W±/Z-bosons provide the first constraint on the sea-quark Sivers function and contributes to the tests of the predicted sign change. The tilt of the dijet opening angle provides a direct access to the first Mellin momentum of the Sivers function and avoids the spin-correlated fragmentation contributions. The novel measurements of the azimuthal distributions of identified hadrons in jets and spin-dependent dihadron correlations directly probe the collinear quark transversity in the proton, with the former coupled to the transverse momentum dependent (TMD) Collins fragmentation function and the latter to the dihadron interference fragmentation function. These measurements shed lights on Sivers function, quark transversity and spin-dependent fragmentation functions in both collinear and TMD formalism. In this proceeding, recent jet results on both the longitudinal and transverse spin structure of the proton from STAR are presented. [ABSTRACT FROM AUTHOR]

Ultraperipheral collisions of relativistic heavy ion beams lead to a diverse set of photon-nucleus (photonuclear) interactions. The measurements of particles and their interaction produced in photonuclear reactions can shed light on the QCD dynamics of these novel, extremely asymmetric colliding systems, with energies between those available at RHIC and the LHC. Previous studies by ATLAS indicate significant elliptic and triangular flow coefficients in these events [1]. Thus, it is imperative to check these events for other potential QGP signatures including radial flow, strangeness enhancement, and enhanced baryon/meson production. This proceeding presents the measurement of charged hadron yields in photonuclear collisions using 5.02 TeV Pb+Pb data collected in 2018 by ATLAS, with a dedicated photo-nuclear event trigger. The charged hadron yields are presented as a function of pseudorapidity and transverse momentum in different categories of event multiplicity. The results are compared with 5.02 TeV p+Pb data collected in 2016 by ATLAS, at the same event multiplicities. The results are also compared with calculations from DPMJET and hydrodynamic-based models. These comparisons enable detailed characterizations of photonuclear collision properties, including the photon energy distribution, and whether small QGP droplets may be formed. [ABSTRACT FROM AUTHOR]

An upgrade to the STAR detector system at forward rapidities has been completed before the RHIC RUN 2022. It consists of the Forward Tracking System (FTS) and the Forward Calorimeter System (FCS). The Forward Tracking System is composed of a Silicon Tracker and a small-strip Thin Gap Chamber Tracker. The Forward Calorimeter System contains an Electromagnetic Calorimeter and a Hadronic Calorimeter. These systems cover the pseudorapidity region of 2.5 < η < 4, providing detection capabilities for neutral pions, photons, electrons, jets, and charged hadrons. This enables the STAR experiment to study cold QCD physics at very high and low regions of Bjorken x and to explore the longitudinal structure of the initial state in relativistic heavyion collisions by measuring the decorrelations at large η. This proceeding will introduce the STAR forward upgrade, its current status, and its performance during the STAR Run22. [ABSTRACT FROM AUTHOR]

Heavy meson production in reactions with nuclei is an active new frontier to understand QCD dynamics and the process of hadronization in nuclear matter. Measurements in various colliding systems at RHIC and LHC, including Pb-Pb, Xe-Xe, O-O, p-Pb, and p-O, enable precision tests of the medium-size, temperature, and mass dependencies of the in-medium parton propagation and shower formation. We employ a coupled DGLAP evolution framework that takes advantage of splitting functions recently obtained in softcollinear effective theory with Glauber gluons (SCETG) and hard thermal loop (HTL) motivated collisional energy loss effects. With jet quenching effects constrained to the nuclear modification factor of charged hadrons in Pb-Pb collisions at 5.02 TeV, we present predictions for light and heavy-meson in Xe-Xe, O-O and p-Pb collisions at the LHC.We find that the nuclear modification scales non-trivially with the quark mass and medium properties. In particular, there can be sizeable collision-induced attenuation of heavy mesons in small systems such as oxygen-oxygen and high-multiplicity p-Pb events. Finally, we analyze the impact of different models of initial-state parton dynamics on the search for QGP signatures in small colliding systems. [ABSTRACT FROM AUTHOR]

The JETSCAPE Collaboration reports the first multi-messenger study of the QGP jet transport parameter q^ using Bayesian inference, incorporating all available hadron and jet inclusive yield and jet substructure data from RHIC and the LHC. The theoretical model utilizes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution. Tension is observed when constraining q^ for different kinematic cuts of the inclusive hadron data. The addition of substructure data is shown to improve the constraint on q^, without inducing tension with the constraint due to inclusive observables. These studies provide new insight into the mechanisms of jet interactions in matter, and point to next steps in the field for comprehensive understanding of jet quenching as a probe of the QGP. [ABSTRACT FROM AUTHOR]

The LHCb spectrometer has the unique capability to function as a fixed-target experiment by injecting gas into the LHC beam pipe while proton or ion beams are circulating. The resulting beam+gas collisions have a center of mass energy intermediate to previous fixed-target experiments and the top RHIC energy for AA collisions, cover an unexplored kinematic range and allow systems of different size to be studied. Here we present new results on open charm, J/ψ, and ψ(2S) production from pNe and PbNe fixed-target collisions at LHCb. Comparisons with various theoretical models of particle production and transport through the nucleus will be discussed. [ABSTRACT FROM AUTHOR]

Within a (3+1)D viscous hydrodynamic model we compute anisotropic flow in small system collisions as performed at the Relativistic Heavy Ion Collider and measured by the STAR and PHENIX Collaborations. We emphasize the importance of the rapidity dependence of the geometry for interpreting the differences encountered in measurements by the two collaborations. [ABSTRACT FROM AUTHOR]

Strangeness enhancement has long been considered a signature of quark-gluon plasma formation in heavy-ion collisions. Recently, strangeness enhancement has also been observed in small systems at the Large Hadron Collider (LHC), but the underlying physics is not yet fully understood. This motivates us to study of strange hadron production in small system at Relativistic Heavy Ion Collider (RHIC). In this proceedings, we present new measurements of strange hadrons (KS0, Λ(¯Λ)) in d+Au collisions at √SNN = 200 GeV, collected by the STAR experiment in 2016. We will report pT spectra, dN/dy, , nuclear modification factor and YAsym of these particles in d+Au collisions. [ABSTRACT FROM AUTHOR]

The equation of state of the quark gluon plasma is a key ingredient of heavy ion phenomenology. In addition to the traditional Taylor method, several novel approximation schemes have been proposed with the aim of calculating it at finite baryon density. In order to gain a pragmatic understanding of the limits of these schemes, we compare them to direct results at μB > 0, using reweighting techniques free from an overlap problem. We use 2stout improved staggered fermions with 8 time-slices and cover the entire RHIC BES range in the baryochemical potential, up to μB/T = 3. This work is based on Ref. [1]. [ABSTRACT FROM AUTHOR]

We report on measurements of light charged hadron production in Au+Au collisions at √SNN = 14.6, 19.6, 27, and 54.4 GeV from the second phase of the beam energy scan (BES-II) program at RHIC. Transverse mass spectra and rapidity density distributions of π±, K±, p, and ¯p are measured as a function of collision energy, centrality, and rapidity. This work extends the previously published BES-I mid-rapidity (|y| < 0.1) measurement to a rapidity of 0.9. This new rapidity dependence highlights the effects of baryon stopping for proton yields and the different production mechanisms of π± and K±. The relative abundance of these light hadrons indicates different thermodynamic environments at different energies, centralities, and rapidities. The temperature (T) and chemical potentials (μB and μS) at chemical freeze-out are reported with their dependence on rapidity to further understand the QCD phase diagram. [ABSTRACT FROM AUTHOR]

Using an eighth-order Taylor expansion in baryon chemical potential, we recently obtained the (2+1)-flavor QCD equation of state (EoS) at nonzero conserved charge chemical potentials from the lattice. We focused on strangeness-neutral, isospin-symmetric QCD matter, which closely resembles the situation encountered in heavy-ion collision experiments. Using this EoS, we present here results on various QCD material parameters; in particular we compute the specific heat, speed of sound, and compressibility along appropriate lines of constant physics. We show that in the entire range relevant for the beam energy scan at RHIC, the specific heat, speed of sound, and compressibility show no indication for an approach to critical behavior that one would expect close to a possibly existing critical endpoint. [ABSTRACT FROM AUTHOR]

We construct a dynamical model for high-energy heavy-ion collisions based on the relativistic resistive magneto-hydrodynamic framework. Using the code, we investigate the charge-dependent anisotropic flow in √SNN = 200 GeV Au+Au collisions and Cu+Au collisions at RHIC. We conclude that the charge-dependent anisotropic flow is a good probe to extract the electrical conductivity of QGP medium. [ABSTRACT FROM AUTHOR]

The state-of-the-art theoretical formalism for a covariant description of non-Gaussian fluctuation dynamics in relativistic fluids is discussed. [ABSTRACT FROM AUTHOR]

Considering applications to relativistic heavy-ion collisions, we develop a rapidity-dependent thermal model that includes thermal smearing effect and longitudinal boost. We calibrate the model with thermal yields obtained from a multistage hydrodynamic simulation. Through Bayesian analysis, we find that our model extracts freeze-out thermodynamics with better precision than rapidity-independent models. The potential of such a model to constrain longitudinal flow from data is also demonstrated. [ABSTRACT FROM AUTHOR]

Viscous hydrodynamics serves as a successful mesoscopic description of the QGP produced in relativistic heavy-ion collisions. In order to investigate, how such an effective description emerges from the underlying microscopic dynamics we calculate the hydrodynamic and non-hydrodynamic modes of linear response in the sound channel from a first-principle calculation in kinetic theory. We do this with a new approach wherein we linearize and discretize the collision kernel to calculate eigenvalues directly. This allows us to study the Green's functions at any point in time or frequency space. Our study focuses on scalar theory with quartic interaction and we find that the analytic structure of Green's functions in the complex plane is far more complicated than just poles or cuts which is the first step towards an equivalent study in QCD kinetic theory. [ABSTRACT FROM AUTHOR]

We study cold nuclear matter effects on Drell-Yan production at small and moderate pT in proton/pion-nucleus collisions using a new transversemomentum dependent (TMD) factorization framework. Both collisional broadening and medium-induced radiative corrections in the initial state are considered in the soft-collinear effective theory with Glauber gluons (SCETG) approach. We demonstrate that in-medium bremsstrahlung exhibits rapidity divergences as x → 1 and collinear divergences at the endpoints x = 0, 1 of the medium-induced emission spectra. We further show that the rapidity divergences lead to the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution of the collision kernel and can be resummed into the transverse momentum broadening of particle production. In turn, the endpoints divergences of in-medium radiation can be resummed through the collinear evolution of parton densities in nuclear matter. The TMD factorization framework is applied to understand the transverse-momentum spectra of Drell-Yan pair production in pA and πA collisions and provides calculations with improved accuracy for hadron production in cold QCD processes at RHIC and LHC. [ABSTRACT FROM AUTHOR]

Particle correlations are a powerful tool to study the properties of the bulk nuclear matter produced in relativistic heavy ion collisions. The momentum correlations between identical particles originating from the same particleemitting source, referred to as the Bose-Einstein correlations, measure scales that are related to the geometrical size of the source. The two-particle azimuthal angular correlations measure the spatial anisotropy of produced particles, providing information on collective phenomena arising in the dense nuclear medium. This contribution will discuss new LHCb measurements of Bose- Einstein correlations and, for the first time, the collective flow coefficients in the far forward rapidity region. [ABSTRACT FROM AUTHOR]

The investigation of the production mechanism of light (anti)(hyper)nuclei in ultrarelativistic hadronic collisions is one of the main topics in modern nuclear physics. The ALICE Collaboration has significantly contributed to this specific field of research with systematic measurements of the production of (anti)(hyper)nuclei in different collision systems and centre-ofmass energies provided by the Large Hadron Collider. Measurements of the properties of hypernuclei, such as their lifetimes and binding energies, provide information on the hadronic interaction between hyperons and nucleons, which is complementary to that obtained from correlation measurements. In this contribution, recent results on the production of (anti)(hyper)nuclei measured with ALICE during the LHC Run 2 in different collision systems will be presented. These results will be discussed within the context of the statistical hadronization model and baryon coalescence. For the first time, the observations of the (anti)hyperhydrogen-4 and (anti)hyperhelium-4 in Pb–Pb collisions at 5.02 TeV will be shown. Moreover, new results on (anti)(hyper)nuclei measurements obtained using the LHC Run 3 data will be presented. [ABSTRACT FROM AUTHOR]

The lifetimes of hadronic resonances are comparable to the one of the hadron gas phase created in the late stages of high-energy nuclear collisions. Therefore, a significant fraction of resonances decay inside a high-density medium and their decay daughters rescatter with nearby hadrons destroying their initial kinematic correlations. The competing effect of resonance regeneration via pseudo-elastic interactions of hadrons interplays between the rescattering effect, modifying the measured yields and transverse-momentum spectra of hadronic resonances. These effects are studied by measuring the production yield ratio of resonances to the corresponding long-lived particle as a function of the hadronic lifetime, i.e. charged-particle multiplicity. In addition, measurements of the differential yields of resonances with different masses, quark content, and quantum numbers help in understanding particle production mechanisms, strangeness production, and parton energy loss. This article reports recent ALICE measurements on resonances and the use of the experimental input in a partial chemical equilibrium-based thermal model to constrain the kinetic freezeout temperature. This is a novel procedure that is independent of assumptions on the flow velocity profile and the freeze-out hypersurface. [ABSTRACT FROM AUTHOR]

Since the discovery of the jet quenching at RHIC, the in-medium interaction of hard scattered partons with the nuclear medium created by highenergy heavy-ion collisions has been an excellent tool to understand not only the transport properties of the medium but also its time evolution towards hadronization. The multi-differential measurement of the high momentum twoparticle correlations can probe a particular space-time window as a function of energy transfer. Comparing the correlations with the prompt photon-triggered hadron spectra, one can extract the property of the medium from various aspects and contribute to distinct models. The PHENIX experiment at RHIC has collected its highest statistics of the γ and π0 triggered hadron events in Au+Au collisions at √SNN = 200 GeV in the RHIC Year-2014 run, and measured not only the inclusive spectra of the triggered hadrons but also the angle and energy dependent IAA and DAA. We will discuss the in-medium modification of the energy-space structure of the jets at the RHIC energies with the results obtained. [ABSTRACT FROM AUTHOR]

Prompt photons are created in the early stages of heavy ion collisions and traverse the QGP medium without any interaction. Therefore, photontriggered jets can be used to study the jet quenching in the QGP medium. In this work, photon-triggered jets are studied through different jet and jet substructure observables for different collision systems and energies using the JETSCAPE framework. Since the multistage evolution used in the JETSCAPE framework is adequate to describe a wide range of experimental observables simultaneously using the same parameter tune, we use the same parameters tuned for jet and leading hadron studies. The same isolation criteria used in the experimental analysis are used to identify prompt photons for better comparison. For the first time, high-accuracy JETSCAPE results are compared with multi-energy LHC and RHIC measurements to better understand the deviations observed in prior studies. This study highlights the importance of multistage evolution for the simultaneous description of experimental observables through different collision systems and energies using a single parameter tune. [ABSTRACT FROM AUTHOR]

We report measurements of the inclusive charged-particle jet yield in central Pb–Pb collisions at √SNN = 5.02 TeV. Uncorrelated background is suppressed by a novel mixed-event technique, enabling extension of the jet RAA measurement down to pT = 13.5 GeV/c, with kinematic overlap with RHIC jet measurements. We also present measurements of inclusive charged-particle jet v2 in semi-central Pb–Pb collisions at √SNN = 5.02 TeV, and azimuthal dependence of jet yield suppression for event topologies selected using eventshape engineering. [ABSTRACT FROM AUTHOR]

Jets are produced in early stages of heavy-ion collisions and undergo modified showering in the quark-gluon plasma (QGP) medium relative to a vacuum case. These modifications can be measured using observables like jet momentum profile and generalized angularities to study the details of jetmedium interactions. Jet momentum profile (ρ(r)) encodes radially differential information about jet broadening and has shown migration of charged energy towards the jet periphery in Pb+Pb collisions at the LHC. Measurements of generalized angularities (girth g and momentum dispersion pTD) and LeSub (difference between leading and subleading constituents) from Pb+Pb collisions at the LHC show harder, or more quark-like jet fragmentation, in the presence of the medium. Measuring these distributions in heavy-ion collisions at RHIC will help us further characterize the jet-medium interactions in a phase-space region complimentary to that of the LHC. In this contribution, we present the first measurements of fully corrected g, pTD and LeSub observables using hard-core jets in Au+Au collisions at √SNN = 200 GeV, collected by the STAR experiment at RHIC. [ABSTRACT FROM AUTHOR]

Recently, a method was developed for implementing arbitrary shortrange nucleon-nucleon correlations in Monte Carlo sampled nuclei (as well as deformations of the 1-body nuclear density). We use this method to implement realistic 2-body correlations in a sample of nuclei for use in simulations of relativistic heavy-ion collisions and we quantify the statistical benefits. These results demonstrate that the method can be used to easily implement an arbitrary correlation function, and systematically study the effects of correlations using significantly less resources than is necessary with traditional methods. [ABSTRACT FROM AUTHOR]

The forward single hadron production process is an important benchmark process for investigating the emergent properties of gluon saturation or the dense gluon system. We present our recent work [1] in which we improve the prediction accuracy of the next-to-leading order calculation of forward single hadron productions in high-p⊥ regions by implementing the threshold resummations in the Color Glass Condensate framework. Our resummed formula provides accurate descriptions of all related data across a range of energies from RHIC to the LHC. This work sheds light on the path for precision study of Color Glass Condensate based on experimental data. [ABSTRACT FROM AUTHOR]

Results on collisions of 16O nuclei performed at the Relativistic Heavy Ion Collider (RHIC) have been presented for the first time at Quark Matter 2023 by the STAR collaboration. 16O+16O collisions are also expected to take place in the near future at the Large Hadron Collider (LHC) at much higher beam energies. We explore the potential of beam-energy-dependent studies for this system to probe small-x dynamics and QCD evolution. We perform 3 + 1D IP-Glasma simulations to predict the rapidity dependence of the initial geometry of light-ion collisions, focusing on 16O+16O and 20Ne+20Ne collisions at √SNN = 70 GeV and 7 TeV. The choice of 20Ne is motivated by its strongly elongated geometry, which may respond differently to the effect of the highenergy evolution compared to the more spherical 16O. We find that smearing induced by soft gluon production at high energy causes mild variations in the initial-state eccentricities as a function of the collision energy. These effects could be resolved in future experiments and deserve further investigation. [ABSTRACT FROM AUTHOR]

Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions with good description of D mesons RAA(pT) and v2,3(pT) and leading to the evaluation of the spatial diffusion coefficient Ds(T). With an event-by-event full Boltzmann transport approach followed by a hybrid hadronization via coalescence plus fragmentation, we show RAA(pT), v2(pT) down to pT → 0 for D and B mesons. We find that QPM approach is able to correctly predict first available data on RAA(pT) and v2(pT) of single-electron from B mesons decays measured by ALICE. A significant breaking of the expected scaling of the thermalization time τth with MQ/T is found. Charm quark Ds(T) is about 50% larger than the asymptotic value for MQ → ∞, while the bottom Ds(T) is only 20% higher. In the infinite mass limit the Ds(T) is consistent with recent lQCD calculations with dynamical quarks. [ABSTRACT FROM AUTHOR]

The PHENIX experiment at RHIC has a unique large rapidity coverage (1.2 < |y| < 2.2) for heavy flavor studies in heavy-ion collisions. This kinematic region has a smaller particle density and may undergo different nuclear effects before and after the hard process when compared to mid-rapidity production. The latest PHENIX runs contain a large data set which allows, for the first time, the study of heavy flavor and J/ψ flow at the large rapidity region in Au+Au collisions at √SNN =200 GeV. This measurement has the potential to reveal a medium evolution distinct from that known at mid-rapidity. [ABSTRACT FROM AUTHOR]

The sPHENIX experiment at RHIC utilizes the first new heavy ion detector since the switch on of the LHC experiments. It's optimized for precision jet and heavy flavor physics measurements, and recorded its first collisions in spring 2023. sPHENIX uses a tracking system with streaming readout and barrel calorimetry to reconstruct the collision topology. Event plane detectors, minimum bias detectors and zero-degree calorimeters are used to characterize the event. The streaming readout detectors are capable of recording 10% of the minimum bias rate, in addition to triggered events, in p+p collisions which will enable unabated, precision b-hadron and heavy flavor jet measurements at RHIC. An AI-assisted hardware trigger demonstrator is under development to sample the remaining 90% of minimum-bias p+p collisions with an aim for further deployment at the EIC. [ABSTRACT FROM AUTHOR]

We report the first results on collision energy and particle mass dependence of directed flow v1 of light- and hyper-nuclei in mid-central Au+Au collisions at center of mass energies per nucleon pair of 3.0, 3.2, 3.5, and 3.9 GeV. All data have been collected by the STAR experiment in the fixed-target mode during the second phase of the RHIC beam energy scan. The mid-rapidity v1 slope, dv1/dy|y=0, of hyper-nuclei shows a similar energy and particle mass dependence to that of light-nuclei. The results suggest that the coalescence mechanism plays a dominant role in the formation of light- and hyper-nuclei. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Photons provide snapshots of the evolution of relativistic heavy-ion collisions as they are emitted at all stages and do not interact with the medium strongly. With RHIC, measurements of low momentum direct-photons are made possible across different system sizes and beam energies. An excess of direct-photons, above the prompt photon production from hard scattering processes, is observed for a system size corresponding to dNch/dη of 20-30, with a large azimuthal anisotropy and a characteristic dependence on collision centrality. In addition to the results for direct-photon spectra, azimuthal anisotropies of direct-photons in Au+Au collisions at √SNN = 200 GeV are also discussed, thereby, shedding light on the long-standing direct-photon puzzle. [ABSTRACT FROM AUTHOR]

The lepton pair production rate at finite temperature and at nextto-leading-order (NLO) is calculated for quark-gluon plasma at non-zero net baryon density. Yields are obtained using a (3+1)D multicomponent simulation capable of reproducing hadronic observables measured in the RHIC Beam Energy Scan (BES). Spectra of intermediate invariant mass dileptons are compared with measurements from the STAR collaboration. The result of a study where the temperature information obtained from the dilepton spectrum from heavyion collisions performed at different energies and centralities is presented. [ABSTRACT FROM AUTHOR]

Dielectrons emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions offer an effective way to probe the medium properties, as they do not interact via the strong force. The rate of the dielectron emission is proportional to the medium's electromagnetic spectral function. In the dielectron invariant mass range from 400 MeV/c2 to 800 MeV/c2, the spectral function probes the in-medium ρ meson propagator which is sensitive to the medium's properties including the total baryon density and the temperature. Meanwhile, the low energy range of the spectral function provides information about the medium's electrical conductivity. Therefore, by measuring thermal dielectron production, we can study the microscopic interactions between the electromagnetic current and the medium. The STAR experiment has recorded large datasets of Au+Au collisions during the Beam Energy Scan Phase-II (BES-II) program, spanning center-of-mass energies between √SNN = 3.0 and 19.6 GeV with detector upgrades that benefit the dielectron measurement via extended transverse momentum and rapidity coverages as well as enhanced particle identification capability. In these proceedings, we will report on the measurements of thermal dielectrons produced in Au+Au collisions at √SNN = 7.7, 14.6, and 19.6 GeV using the STAR experiment. [ABSTRACT FROM AUTHOR]

A hot and dense matter exhibiting collective flow behavior with almost no viscous dissipation has been discovered in ultrarelativistic nuclear collisions. To constrain the fundamental degrees of freedom and equation of state of this matter, these proceedings present an extraction of its speed of sound using head-on lead-lead collision data collected by the CMS experiment at a center-of-mass energy per nucleon pair of 5.02 TeV. The measurement is based on an analysis of the observed charged multiplicity dependence of the average particle transverse momentum in ultra-central events (impact parameter of nearly zero). This variable probes the system temperature as a function of entropy density at a fixed volume. Results are compared with hydrodynamic simulations and lattice quantum chromodynamics (QCD) predictions of the equation of state at high temperatures and small chemical potential. Implications to search for QCD phase transition and the critical point are discussed. [ABSTRACT FROM AUTHOR]

The moments of proton and net-proton multiplicity distributions are observables expected to be sensitive to the QCD critical point and the nature of the QCD phase transition from QGP to hadron gas. Hyper-order cumulants are measured in wide centrality bins in STAR BES-I data and found to be qualitatively consistent with trends predicted by lattice QCD which finds a cross-over phase transition at low μB. Data collected at √SNN = 3 GeV in BES-II exhibit trends opposite of those observed in higher energy collisions which may suggest the dominance of hadronic interactions at this energy. The variance of proton multiplicity distributions in azimuthal partitions is measured to search for signals of clustering indicative of a first-order phase transition. A strong dependence on the event multiplicity is observed. This dependence is independent of energy in AMPT while in STAR data a significant trend with energy is observed. [ABSTRACT FROM AUTHOR]

We report our recent study on the global and local polarization of Λ hyperons in Au+Au collisions at RHIC-BES energies within the (3+1)- dimensional CLVisc hydrodynamics framework. We present our numerical results for the global polarization as a function of collision energies and the local polarization along the beam direction as functions of azimuthal angle in 20 − 50% centrality at √SNN = 7.7 GeV Au+Au collision energy. We have discussed the effects of initial conditions, Spin Hall effect and baryon diffusion. [ABSTRACT FROM AUTHOR]

In these proceedings, we present transverse momentum dependence of the mid-rapidity slope of directed flow (dv1/dy|y=0) for π+ and KS0 in Au + Au collisions at √SNN = 3.0, 3.2, 3.5, and 3.9 GeV. Both π+ and KS0 show negative v1 slope at low pT (pT < 0.6 GeV/c). Collision energy dependence of v1 slope and pT -integrated v2 for π±, KS0, and Λ are also presented. A comparison to JAM model calculations indicates that spectator shadowing can lead to anti-flow at low pT. In addition, a breaking of the Number of Constitute Quark (NCQ) scaling of elliptic flow (v2) is observed at √SNN = 3.2 GeV, which implies the dominance of hadronic degrees of freedom occurs in collisions at √SNN = 3.2 GeV and below. [ABSTRACT FROM AUTHOR]

It is of fundamental interest to understand the carrier of conserved quantum charges within protons and nuclei at high energy. Preliminary data from isobar collisions at RHIC reveal a scaled net-baryon to net-electric charge ratio (B/ΔQ × ΔZ/A) at midrapidity between 1.2 and 2, consistent with string junction model predictions. Here, we compute the initial stage scaled net-baryon to net-electric charge ratio for isobar collisions. Our model incorporates a realization of the string junction model and models the nuclear structure. Our predictions identify the baseline expectations for such measurement and quantify the impact of the nuclear structure. [ABSTRACT FROM AUTHOR]

A novel three-fluid dynamical model for simulations of heavy-ion collisions at RHIC Beam Energy Scan programme, called MUFFIN, has been developed. The novelty consists of modular inclusion of the Equation of State, use of hyperbolic coordinates that allow to simulate higher collision energies, and fluctuating initial conditions. The model reproduces rapidity and pt spectra of collisions from √SNN = 7.7 to 62.4 GeV. Ideal fluid is assumed, and the elliptic flow is over-predicted, particularly at lower collision energies. [ABSTRACT FROM AUTHOR]

In these proceedings, we present the measurements of global polarization for Λ, ¯Λ with the high-statistics data collected by the STAR experiment for isobar (Ru+Ru, Zr+Zr) collisions at √SNN = 200 GeV and Au+Au collisions at √SNN = 19.6, 27 GeV. These measurements allow us to study possible magnetic field driven effects through the polarization difference between Λ and ¯Λ and system size dependence of global polarization. Furthermore, we present the first measurements of Λ, ¯Λ hyperon local polarization in isobar collisions at √SNN = 200 GeV and Au+Au collisions at √SNN = 19.6, 27 GeV. Comparisons with previous measurements in Au+Au and Pb+Pb collisions at RHIC and LHC provide important insights into the collision system size and energy dependence of the vorticities. The local polarization measurements at lower beam energies can probe the predicted baryonic spin hall effect in a dense baryonic environment in heavy-ion collisions. [ABSTRACT FROM AUTHOR]

In these proceedings, we present new measurements from STAR of the global spin alignment(ρ00) of ϕ mesons in Au+Au collisions at √SNN = 19.6, 14.6 GeV using BES-II data and of J/ψ mesons in isobar collisions 4496Ru + 4496Ru and 4096Zr + 4096Zr at √SNN = 200 GeV. The energy-dependent spin alignment for ϕ mesons from BES-II data is consistent with that published from BES-I and showcases a significant improvement in precision. We performed a new measurement assessing the rapidity dependence of ϕ meson ρ00, and our findings are consistent with theoretical predictions. The global spin alignment of J/ψ mesons with respect to first order event plane aligns with a value of 1/3 within the statistical error. Additionally, we discuss the procedure of measuring the global spin alignment of ρ0 mesons at RHIC and provide the projection for errors. [ABSTRACT FROM AUTHOR]

We present directed flow of protons and pions, as well as mean polarization of Λ and ¯Λ hyperons computed for Au-Au collisions at √SNN = 5 ... 19.6 GeV in MUFFIN model. MUlti Fluid simulation for Fast IoN collisions, or MUFFIN, is a state-of-the-art 3-fluid dynamic model for simulating heavy-ion collisions in the region from a few to a hundred GeV center-of-mass energy. Whereas MUFFIN succeeds to reproduce basic observables in the collision energy range of interest, the slope of the directed flow at mid-rapidity is much steeper as compared to the data, it has unclear EoS dependence and final-state hadronic cascade affects this observable significantly. The excitation function of the Λ polarization shows a significant splitting between polarizations of Λ and ¯Λ, which challenges a widespread interpretation that the splitting is affected mainly by the late-stage magnetic field. [ABSTRACT FROM AUTHOR]

The sPHENIX project is a new collider experiment at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory (BNL). It aims to study the Quark-Gluon Plasma and cold Quantum Chromodynamics (QCD) by measuring photons, jets, jet correlations, and the Upsilon family with high precision. To achieve these goals, a precise tracking system is necessary. The tracking system of the sPHENIX detector consists of the MVTX, INTT, TPC, and TPOT. INTT is a two-layer barrel silicon tracker that plays a unique role among the sPHENIX tracking detectors. It is capable of bridging the tracks of MVTX and TPC. In addition, its precise timing resolution enables INTT to associate individual tracks with events to eliminate pile-up events. The INTT barrel installation and cabling were completed in March 2023. We have since commissioned and confirmed the detector responses. The INTT status, and performance evaluated by beam and cosmic rays are described in this proceedings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this Quark Matter 2023 conference proceedings, recent measurements at RHIC and the LHC and theoretical developments on the jet-induced medium response are summarized. [ABSTRACT FROM AUTHOR]

In this paper, we provide an exploration of the interrelated topics of chirality, vorticity, and spin polarization in relativistic heavy ion collisions. Our discussion delves into the intricate relationships among these phenomena, examining the recent measurements conducted at both RHIC and LHC.We review the challenges faced, the progress made, and the current state of understanding regarding hot QCD matter under rotation. [ABSTRACT FROM AUTHOR]

Ultra-relativistic heavy-ion collisions produce extremely strong electromagnetic field which provide a uniquely intense and energetic source of photons. The photons manifest from such ultra-Lorentz contracted electromagnetic fields have, in recent years, enabled unique advances in Quantum Electrodynamics (QED) and Quantum Chromodynamics (QCD). This manuscript summarizes recent progress across the experimental and theoretical landscape as of 2023 and ends with a look to possible future advancements. [ABSTRACT FROM AUTHOR]

sPHENIX is the first new major detector at RHIC in over twenty years. It is designed for pioneering studies of the Quark Gluon Plasma and Cold QCD phenomena using high-pT jet and heavy flavor probes with a broad kinematic reach and a capability to take large statistics sets of A+A, p+p and p+A data. sPHENIX construction was completed in April 2023. It was commissioned and took first Au+Au data in the RHIC 2023 Run. This paper describes the details of the detector design, challenges of sPHENIX construction, progress on the commissioning and first data from the RHIC 2023 run. [ABSTRACT FROM AUTHOR]

The STAR experiment covers a wide range of energies and collisions thanks to RHIC's versatility and STAR's recent detector upgrades. In this contribution to the proceedings of the 2023 QuarkMatter conference, we highlight our new results from the Beam Energy Scan, system-size scans at top RHIC energies using a broad range of experimental probes. [ABSTRACT FROM AUTHOR]