Observation of the Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC

The STAR collaboration
2025.
Inspire Record 2907591 DOI 10.17182/hepdata.159489

Partonic collectivity is one of the necessary signatures for the formation of Quark-Gluon-Plasma in high-energy nuclear collisions. Number of Constituent Quarks (NCQ) scaling has been observed for light hadron elliptic flow $v_2$ in top energy nuclear collisions at RHIC and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this letter, a systematic analysis of $v_2$ of $\pi^{\pm}$, $K^{\pm}$, $K^{0}_{S}$, $p$ and $\Lambda$ in Au+Au collisions at ${\sqrt{s_{_{\rm{NN}}}}}$ = 3.2, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at RHIC, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of $v_2$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by ${\sqrt{s_{_{\rm{NN}}}}}$ = 4.5 GeV.

72 data tables

$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3 GeV

$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3.2 GeV

$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3.5 GeV

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Measurement of in-medium jet modification using direct photon+jet and $\pi^{0}$+jet correlations in $p+p$ and central Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV

The STAR collaboration Aboona, B.E. ; Adam, J. ; Adamczyk, L. ; et al.
Phys.Rev.Lett. 134 (2025) 232301, 2025.
Inspire Record 2693040 DOI 10.17182/hepdata.144263

The STAR Collaboration presents measurements of the semi-inclusive distribution of charged-particle jets recoiling from energetic direct-photon ($\gamma_{\rm dir}$) and neutral-pion ($\pi^{0}$) triggers in p+p and central Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ GeV over a broad kinematic range, for jet resolution parameters $R$=0.2 and 0.5. Medium-induced jet yield suppression is observed to be larger for $R$=0.2 than for 0.5, reflecting the angular range of jet energy redistribution due to quenching. The predictions of model calculations incorporating jet quenching are not fully consistent with the observations. These results provide new insight into the physical origins of jet quenching.

8 data tables

I_{AA} of Au+Au 0%-15% collisions at sqrt{s_{NN}} = 200 GeV for R = 0.2 of gamma_{dir}+jet with E_{T,trig}= 15-20 GeV.

I_{AA} of Au+Au 0%-15% collisions at sqrt{s_{NN}} = 200 GeV for R = 0.5 of gamma_{dir}+jet with E_{T,trig}= 15-20 GeV.

I_{AA} of Au+Au 0%-15% collisions at sqrt{s_{NN}} = 200 GeV for R = 0.2 of pi^{0}+jet with E_{T,trig}= 11-15 GeV.

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Precision measurement of the longitudinal double-spin asymmetry for dijet production at intermediate pseudorapidity in polarized $pp$ collisions at $\sqrt{s}$ = 200 GeV

The STAR collaboration
2024.
Inspire Record 2854313 DOI 10.17182/hepdata.156055

The STAR Collaboration reports precise measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for dijet production with at least one jet at intermediate pseudorapidity $0.8 < \eta_{\rm jet} < 1.8$ in polarized proton-proton collisions at a center-of-mass energy of 200 GeV. This study explores partons scattered with a longitudinal momentum fraction ($x$) from 0.01 to 0.5, which are predominantly characterized by interactions between high-$x$ valence quarks and low-$x$ gluons. The results are in good agreement with previous measurements at 200 GeV with improved precision and are found to be consistent with the predictions of global analyses that find the gluon polarization to be positive. In contrast, the negative gluon polarization solution from the JAM Collaboration is found to be strongly disfavored.

6 data tables

$A_{LL}$ as a function of parton-level invariant mass for dijets with the East barrel-endcap.

$A_{LL}$ as a function of parton-level invariant mass for dijets with the West barrel-endcap.

$A_{LL}$ as a function of parton-level invariant mass for dijets with the endcap-endcap.

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Measurement of directed flow in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV with the STAR Event Plane Detector

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
Phys.Rev.C 111 (2025) 014906, 2025.
Inspire Record 2808515 DOI 10.17182/hepdata.153808

In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients ($v_n$). The first-order flow coefficient, also referred to as the directed flow ($v_{1}$), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity ($\eta$), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD ($2.1 <|\eta|< 5.1$) and high-statistics BES-II data enables us to extend the $v_{1}$ measurement to the forward and backward $\eta$ regions. In this paper, we present the measurement of $v_{1}$ over a wide $\eta$ range in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV using the STAR EPD. The results of the analysis at $\sqrt{s_{NN}}=$19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable $v_{1}$ at large $\eta$ as was observed experimentally. The model comparison also indicates $v_{1}$ at large $\eta$ might be sensitive to the QGP phase transition.

32 data tables

Directed flow vs pseudorapidity.

Directed flow vs pseudorapidity.

Directed flow vs pseudorapidity.

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Electric charge and strangeness-dependent directed flow splitting of produced quarks in Au+Au collisions

The STAR collaboration
2023.
Inspire Record 2649581 DOI 10.17182/hepdata.139902

We report directed flow ($v_1$) of multistrange baryons ($\Xi$ and $\Omega$) and improved $v_1$ data for $K^{-}$, $\bar{p}$, $\bar{\Lambda}$ and $\phi$ in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=$27 and 200 GeV from the STAR at the Relativistic Heavy Ion Collider (RHIC). We focus on particles whose constituent quarks are not transported from beam rapidity rather produced in the collisions. In midcentral collisions, we observe a coalescence sum rule for hadron combinations with identical quark content and a difference (``splitting'') in the slope of $v_1$ vs. rapidity for combinations having nonidentical quark content. The splitting strength appears to increase with the electric charge difference and strangeness content difference of the constituent quarks in the combinations, consistent with an electromagnetic effect. The peripheral collision statistics are insufficient to draw firm conclusions.

16 data tables

Directed flow of $\Xi^{-}$ and $\overline{\Xi}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 27$ GeV.

Directed flow of $\Omega^{-}$ and $\overline{\Omega}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 27$ GeV.

Directed flow of $\Xi^{-}$ and $\overline{\Xi}^{+}$ versus rapidity for 10-40\% Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV.

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Energy Dependence of Polarized $\mathbf{\gamma\gamma\rightarrow e^{+}e^{-}}$ in Peripheral Au+Au Collisions at RHIC

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
Phys.Rev.C 111 (2025) 014909, 2025.
Inspire Record 2809899 DOI 10.17182/hepdata.153885

We report the differential yields at mid-rapidity of the Breit-Wheeler process ($\gamma\gamma\rightarrow e^{+}e^{-}$) in peripheral Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}} = $ 54.4 GeV and 200 GeV with the STAR experiment at RHIC, as a function of energy $\sqrt{s_{_{\rm{NN}}}}$, $e^{+}e^{-}$ transverse momentum $p_{\rm T}$, $p_{\rm T}^{2}$, invariant mass $M_{ee}$ and azimuthal angle. In the invariant mass range of 0.4 $<$$M_{ee}$$<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_{\rm T}$$ < $0.15 GeV/$c$), the yields increase while the pair $\sqrt{\langle p_{\rm T}^{2} \rangle}$ decreases with increasing $\sqrt{s_{_{\rm{NN}}}}$, a feature is correctly predicted by the QED calculation. The energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

30 data tables

'54.4 GeV, Centrality: 40-60%'

'54.4 GeV, Centrality: 60-80%'

'54.4 GeV, Centrality: 80-100%'

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Production of Protons and Light Nuclei in Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV with the STAR Detector

The STAR collaboration Abdulhamid, Muhammad ; Aboona, Bassam ; Adam, Jaroslav ; et al.
Phys.Rev.C 110 (2024) 054911, 2024.
Inspire Record 2724476 DOI 10.17182/hepdata.145837

We report the systematic measurement of protons and light nuclei production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum ($p_{T}$) spectra of protons ($p$), deuterons ($d$), tritons ($t$), $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ are measured from mid-rapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields ($dN/dy$), average transverse momentum ($\langle p_{T}\rangle$), yield ratios ($d/p$, $t/p$,$^{3}\mathrm{He}/p$, $^{4}\mathrm{He}/p$), as well as the coalescence parameters ($B_2$, $B_3$). The 4$\pi$ yields for various particles are determined by utilizing the measured rapidity distributions, $dN/dy$. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios ($N_{p} \times N_{t} / N_{d}^{2}$) and compare them with various model calculations. The physics implications of those results on the production mechanism of light nuclei and on QCD phase structure are discussed.

53 data tables

Weak decay feed-down fraction of protons (%) at different centralities in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

Transverse momentum spectra of inclusive protons in 0-10% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

Transverse momentum spectra of inclusive protons in 10-20% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

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Strangeness Production in $\sqrt{s_{\rm NN}}=3$ GeV Au+Au Collisions at RHIC

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
JHEP 10 (2024) 139, 2024.
Inspire Record 2807679 DOI 10.17182/hepdata.153884

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=3$ GeV with the STAR experiment at RHIC. $K^0_S$ meson and $\Lambda$ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of $\Lambda$ and $K^0_S$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4$\pi$ yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

19 data tables

dN/dy of lambda for different centrality bins.

dN/dy of Ks0 for different centrality bins.

Rapidity dependence of Lambda/p for different centrality bins.

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Imaging Shapes of Atomic Nuclei in High-Energy Nuclear Collisions

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
Nature 635 (2024) 67-72, 2024.
Inspire Record 2746294 DOI 10.17182/hepdata.147196

Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometer-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the ``collective flow assisted nuclear shape imaging'' method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analyzing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground state Uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.

27 data tables

Data from Figure 2, panel a, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included

Data from Figure 2, panel a, U+U, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included

Data from Figure 2, panel b, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c

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Event activity correlations and jet measurements in p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV

The STAR collaboration Abdulhamid, Muhammad ; Aboona, Bassam ; Adam, Jaroslav ; et al.
Phys.Rev.C 110 (2024) 044908, 2024.
Inspire Record 2777394 DOI 10.17182/hepdata.151385

With the STAR experiment at the BNL Relativisic Heavy Ion Collider, we characterize $\sqrt{s_\mathrm{NN}}$ = 200 GeV p+Au collisions by event activity (EA) measured within the pseudorapidity range $eta$$in$ [-5, -3.4] in the Au-going direction and report correlations between this EA and hard- and soft- scale particle production at midrapidity ($\eta$$\in$ [-1, 1]). At the soft scale, charged particle production in low-EA p+Au collisions is comparable to that in p+p collisions and increases monotonically with increasing EA. At the hard scale, we report measurements of high transverse momentum (pT) jets in events of different EAs. In contrast with the soft particle production, high-pT particle production and EA are found to be inversely related. To investigate whether this is a signal of jet quenching in high-EA events, we also report ratios of pT imbalance and azimuthal separation of dijets in high- and low-EA events. Within our measurement precision, no significant differences are observed, disfavoring the presence of jet quenching in the highest 30% EA p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV.

10 data tables

Distributions of Event Activity (as measured by the BBC) from MB and HT events with the latter satisfying an offline trigger of $E_\mathrm{T}^\mathrm{trig}>4 \mathrm{GeV}$.

Density of charged particles with $p_\mathrm{T}>0.2$ GeV/$c$ and $|\eta|\le0.9$ in ten ranges of EA for MB events and HT events selected with several offline trigger values.

Charged particle density as a function of EA, UE $\eta$, and $p_\mathrm{T,jet}^\mathrm{lead}$ for HT ($E_\mathrm{T}^\mathrm{trig}>4$ GeV) events with $p_\mathrm{T,jet}^\mathrm{raw,lead}>4~\mathrm{GeV}/c$.

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