We present the first measurements of transverse momentum spectra of$\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ at midrapidity ($|y| < 0.1$) in U+Ucollisions at $\sqrt{s_{NN}}$ = 193 GeV with the STAR detector at theRelativistic Heavy Ion Collider (RHIC). The centrality dependence of particleyields, average transverse momenta, particle ratios and kinetic freeze-outparameters are discussed. The results are compared with the published resultsfrom Au+Au collisions at $\sqrt{s_{NN}} =$ 200 GeV in STAR. The results arealso compared to those from A Multi Phase Transport (AMPT) model.
Global polarizations ($P$) of $\Lambda$ ($\bar{\Lambda}$) hyperons have beenobserved in non-central heavy-ion collisions. The strong magnetic fieldprimarily created by the spectator protons in such collisions would split the$\Lambda$ and $\bar{\Lambda}$ global polarizations ($\Delta P = P_{\Lambda} -P_{\bar{\Lambda}} < 0$). Additionally, quantum chromodynamics (QCD) predictstopological charge fluctuations in vacuum, resulting in a chirality imbalanceor parity violation in a local domain. This would give rise to an imbalance($\Delta n = \frac{N_{\text{L}} - N_{\text{R}}}{\langle N_{\text{L}} +N_{\text{R}} \rangle} \neq 0$) between left- and right-handed $\Lambda$($\bar{\Lambda}$) as well as a charge separation along the magnetic field,referred to as the chiral magnetic effect (CME). This charge separation can becharacterized by the parity-even azimuthal correlator ($\Delta\gamma$) andparity-odd azimuthal harmonic observable ($\Delta a_{1}$). Measurements of$\Delta P$, $\Delta\gamma$, and $\Delta a_{1}$ have not led to definitiveconclusions concerning the CME or the magnetic field, and $\Delta n$ has notbeen measured previously. Correlations among these observables may reveal newinsights. This paper reports measurements of correlation between $\Delta n$ and$\Delta a_{1}$, which is sensitive to chirality fluctuations, and correlationbetween $\Delta P$ and $\Delta\gamma$ sensitive to magnetic field in Au+Aucollisions at 27 GeV. For both measurements, no correlations have been observedbeyond statistical fluctuations.
We consider minimal type-A higher-spin (HS) gravity in four dimensions, attree level. We propose new diagrammatic rules for this theory, involving bothFronsdal fields and Didenko-Vasiliev (DV) particles - linearized versions of HSgravity's "BPS black hole". The vertices include a standard minimal couplingbetween particle and gauge field, the Sleight-Taronna cubic vertex for HSfields, and a recently introduced vertex coupling two HS fields to a DVparticle. We show how these ingredients can be combined to reproduce alln-point functions of the theory's holographic dual - the free O(N) vectormodel. Our diagrammatic rules interpolate between the usual ones of fieldtheory and those of string theory. Our construction can be viewed as a bulkrealization of HS algebra.
We report the triton ($t$) production in mid-rapidity ($|y| <$ 0.5) Au+Aucollisions at $\sqrt{s_\mathrm{NN}}$= 7.7--200 GeV measured by the STARexperiment from the first phase of the beam energy scan at the RelativisticHeavy Ion Collider (RHIC). The nuclear compound yield ratio ($\mathrm{N}_t\times \mathrm{N}_p/\mathrm{N}_d^2$), which is predicted to be sensitive to thefluctuation of local neutron density, is observed to decrease monotonicallywith increasing charged-particle multiplicity ($dN_{ch}/d\eta$) and follows ascaling behavior. The $dN_{ch}/d\eta$ dependence of the yield ratio is comparedto calculations from coalescence and thermal models. Enhancements in the yieldratios relative to the coalescence baseline are observed in the 0\%-10\% mostcentral collisions at 19.6 and 27 GeV, with a significance of 2.3$\sigma$ and3.4$\sigma$, respectively, giving a combined significance of 4.1$\sigma$. Theenhancements are not observed in peripheral collisions or model calculationswithout critical fluctuation, and decreases with a smaller $p_{T}$ acceptance.The physics implications of these results on the QCD phase structure and theproduction mechanism of light nuclei in heavy-ion collisions are discussed.
We report here the first observation of directed flow ($v_1$) of thehypernuclei $^3_{\Lambda}$H and $^4_{\Lambda}$H in mid-central Au+Au collisionsat $\sqrt{s_{\rm NN}}$ = 3 GeV at RHIC. These data are taken as part of thebeam energy scan program carried out by the STAR experiment. From 165 $\times$10$^{6}$ events in 5%-40% centrality, about 8400 $^3_{\Lambda}$H and 5200$^4_{\Lambda}$H candidates are reconstructed through two- and three-body decaychannels. We observe that these hypernuclei exhibit significant directed flow.Comparing to that of light nuclei, it is found that the midrapidity $v_1$slopes of $^3_{\Lambda}$H and $^4_{\Lambda}$H follow baryon number scaling,implying that the coalescence is the dominant mechanism for these hypernucleiproduction in such collisions.
The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beamdirection has been measured relative to the second and third harmonic eventplanes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. Thisis the first experimental evidence of the hyperon polarization by thetriangular flow originating from the initial density fluctuations. Theamplitudes of the sine modulation for the second and third harmonic results arecomparable in magnitude, increase from central to peripheral collisions, andshow a mild $p_T$ dependence. The azimuthal angle dependence of thepolarization follows the vorticity pattern expected due to elliptic andtriangular anisotropic flow, and qualitatively disagree with most hydrodynamicmodel calculations based on thermal vorticity and shear induced contributions.The model results based on one of existing implementations of the shearcontribution lead to a correct azimuthal angle dependence, but predictcentrality and $p_T$ dependence that still disagree with experimentalmeasurements. Thus, our results provide stringent constraints on the thermalvorticity and shear-induced contributions to hyperon polarization. Comparisonto previous measurements at RHIC and the LHC for the second-order harmonicresults shows little dependence on the collision system size and collisionenergy.