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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.

We have studied the spin polarization of Λ hyperons in heavy ion collisions at center-of-mass energies s NN = 200 GeV and s NN = 5.02 TeV carried out at RHIC and LHC colliders. We have calculated the mean spin vector at local thermodynamic equilibrium, including all known first-order terms in the gradients of the thermo-hydrodynamic fields, assuming that the hadronization hypersurface has a uniform temperature. We have also included the feed-down contributions to the polarization of Λ stemming from the decays of polarized Σ ∗ and Σ 0 hyperons. The obtained results are in good agreement with the data. In general, the component of the spin vector along the global angular momentum, orthogonal to the reaction plane, shows strong sensitivity to the initial longitudinal flow velocity. Furthermore, the longitudinal component of the spin vector turns out to be very sensitive to the bulk viscosity of the plasma at the highest LHC energy. Therefore, the azimuthal dependence of spin polarization can effectively constrain the initial hydrodynamic conditions and the transport coefficients of the quark gluon plasma.

We present the study of K∗0 in Au+Au collisions at √SNN = 19.6 GeV from RHIC BES-II. The ratio of resonanse to non-resonance (K∗0/K) is shown as function of centrality and center-of-mass energy, which implies the dominance of hadronic re-scattering over regeneration in central A+A collisions. The lower limit of hadronic phase lifetime (tkin − tchem) is also reported using a toy model ansartz. The results are compared with previous RHIC and LHC measurements.

In this contribution, we report the measurement of D0 meson tagged jets in Au+Au collisions at √sNN = 200 GeV by the STAR experiment at RHIC. We present the nuclear modification factor RCP as a function of the jet transverse momentum and transverse momentum fraction of the jet, carried by D0 meson along the jet axis zJet, and the radial profile of the D0 meson. These results are compared to theoretical predictions provided by a hybrid transport model. Additionally, we show the raw measurement of several generalized angularities λκα, which describe the jet substructure. These results may help distinguish between different models describing jet quenching and heavy flavor quark in-medium energy loss.

According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron and a Λ hyperon. With data recorded by the STAR detector 1 – 3 at the Relativistic Heavy Ion Collider, we measure the Λ hyperon binding energy B Λ for the hypertriton, and find that it differs from the widely used value 4 and from predictions 5 – 8 , where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon–nucleon interaction 9 , 10 and have implications for understanding neutron star interiors, where strange matter may be present 11 . A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness, and we observe no deviation from the expected exact symmetry. The STAR collaboration reports a measurement of the mass difference and binding energy of the hypertriton and its antiparticle. This work constrains the hyperon–nucleon interaction and allows us to test the CPT theorem in a nucleus with strangeness.

In recent years there has been much progress on the investigation of the QCD phase diagram with lattice QCD simulations. In this review we focus on the developments in the last two years. Especially the addition of external influences or new parameter ranges yields an increasing number of interesting results. We discuss the progress for small, finite densities from both extrapolation-based methods (Taylor expansion and analytic continuation for imaginary chemical potential) and complex Langevin simulations, for heavy quark bound states (quarkonium), the dependence on the quark masses (Columbia plot) and the influence of a magnetic field. Many of these conditions are relevant for the understanding of both the QCD transition in the early universe and heavy ion collision experiments, which are conducted for example at the LHC and RHIC.

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.

In support of the Electron-Ion Collider (EIC) at Brookhaven National Laboratory (BNL), Jefferson Lab is contributing to the design of three satellite cryogenic plants. These satellite plants will augment BNL’s central plant, which currently provides cryogenics for the Relativistic Heavy Ion Collider (RHIC) at temperatures down to 4.5 Kelvin. The primary role of the satellite plants is to further cool the cryogenic loads to 2 Kelvin, a critical requirement for EIC operations. Secondary objectives of the satellite plant process design include utilization of the existing RHIC cryogenic distribution infrastructure, assurance that the central plant’s present capacity is not exceeded, and optimization of overall cost efficiency. This paper presents a comprehensive evaluation of various process configurations for each satellite plant. It discusses the advantages and disadvantages of each configuration, their integration with the central plant, and the rationale behind the final selection for the satellite plant process design.

To study the microscopic structure of quark–gluon plasma, data from hadronic collisions must be confronted with models that go beyond fluid dynamics. Here, we study a simple kinetic theory model that encompasses fluid dynamics but contains also particle-like excitations in a boost invariant setting with no symmetries in the transverse plane and with large initial momentum asymmetries. We determine the relative weight of fluid dynamical and particle like excitations as a function of system size and energy density by comparing kinetic transport to results from the 0th, 1st and 2nd order gradient expansion of viscous fluid dynamics. We then confront this kinetic theory with data on azimuthal flow coefficients over a wide centrality range in PbPb collisions at the LHC, in AuAu collisions at RHIC, and in pPb collisions at the LHC. Evidence is presented that non-hydrodynamic excitations make the dominant contribution to collective flow signals in pPb collisions at the LHC and contribute significantly to flow in peripheral nucleus–nucleus collisions, while fluid-like excitations dominate collectivity in central nucleus–nucleus collisions at collider energies.

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.