arXiv subjects

The STAR Collaboration

Publications and source records attributed to The STAR Collaboration.

At least 19 recordsLinked to original sources

arXiv2026

Probing (Hyper)Nuclei Wave Functions and Production Mechanisms in $\sqrt{s_{\rm{NN}}}=200$ GeV Isobar Collisions at RHIC

The study of nuclei and hypernuclei production is a powerful tool to investigate the formation mechanism of loosely bound states in high-energy heavy-ion collisions. A key prediction from coalescence models is a strong suppression of the hypertriton (${}^{3}_{\Lambda}\rm{H}$) compared to ${}^{3}\rm{He}$ production in small collision systems due to the larger radius of ${}^{3}_{\Lambda}\rm{H}$. In this letter, the STAR collaboration reports measurements on (hyper)nuclei ($^{3}_{\Lambda}\rm{H}, {}^{3}_{\bar{\Lambda}}\rm{\bar{H}}, {}^{3}\rm{He}, {}^{3}\rm{\overline{He}}, t$) production at mid-rapidity in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\rm{NN}}}=200$ GeV as a function of collision centrality. We find that the ratios $N_{t}N_{p}/N_{d}^{2}$ and $S_{3} =(N_{{}^{3}_{\Lambda}\rm{H}}/N_{{}^{3}_{}\rm{He}})/(N_{\Lambda}/N_{p})$ deviate significantly from thermal model expectations. Coalescence calculations incorporating realistic non-Gaussian wave functions for the $d$ and ${}^{3}_{\Lambda}\rm{H}$ provide an improved description of the data, while Gaussian descriptions of the ${}^{3}_{\Lambda}\rm{H}$ wave function fail to simultaneously reproduce the measured $S_{3}$ and the binding energy of ${}^{3}_{\Lambda}\rm{H}$. These results suggest that the ${}^{3}_{\Lambda}\rm{H}$ wave function contains larger short-distance $d$--$\Lambda$ probability than implied by a Gaussian ansatz, demonstrating the potential of heavy-ion production measurements as a probe of hypernuclear wave functions and the underlying hyperon--nucleon interaction.

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arXiv2026

Observation of the centrality-dependent difference in directed flow between charged kaons and $K^{*0}$ resonances in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.6, 19.6 and 27 GeV

We present the measurement of rapidity-odd directed flow ($v_{1}^{\mathrm{odd}}$) for charged kaons, $\phi$ mesons, and $K^{*0}(\overline{K^{*0}})$ resonances in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.6, 19.6 and 27 GeV. This study includes the first measurement of the $K^{*0}$ resonance $v_{1}^{\mathrm{odd}}$ in heavy-ion collisions. Our measurement shows a centrality-dependent difference in directed flow between charged kaons and $K^{*0}$ resonances, which becomes more pronounced with increasing collision centrality. In contrast, the difference in directed flow between charged kaons and $\phi$ mesons remains nearly independent of centrality. Although anisotropic flow is thought to be developed in the early stages of the collision, for short-lived resonances such as the $K^{*}(892)$ that experience substantial hadronic re-scattering, it remains unclear to what extent the observed $v_{1}^{\mathrm{odd}}$ reflects genuine partonic collectivity in the early stage, and to what extent it is altered by late-stage hadronic interactions and/or reconstruction effects. The present measurement is crucial for disentangling these contributions and addressing this question. Existing hydrodynamic calculations that include a hadronic afterburner based on the UrQMD model indicate that an asymmetric modification of the $K^{*0}$ yield, due to rescattering, relative to the first-order event plane is required to reproduce the observed difference between $v_{1}^{\mathrm{odd}}$ for charged kaons and $K^{*0}$.

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arXiv2026

Hyper-Nuclei $^4_{\Lambda}\hbox{He}$ Production in $\sqrt{s_{\rm{NN}}}$ = 3 GeV Au+Au collisions at RHIC

The STAR experiment reports the first measurement of the $^4_{\Lambda}\hbox{He}$ hyper-nuclei yield as a function of rapidity and transverse momentum in 0-50% central Au+Au collisions at $\sqrt{s_{\rm{NN}}} =$ 3 GeV. The $^4_{\Lambda}\hbox{He}$ is reconstructed through its three-body decay channel, $^4_{\Lambda}\rm{He} \rightarrow {}^{3}\rm{He} + \rm{p} + \pi^-$, with a statistical significance of about 9.5 standard deviations. We find that the yield of $^4_{\Lambda}\hbox{He}$ as a function of rapidity is consistent with that of $^4_{\Lambda}\hbox{H}$, and the rapidity-dependent yield ratio of $^4_{\Lambda}\hbox{He}$/$^4_{\Lambda}\hbox{H}$ is consistent with that of $^3$He/t. All the measurements, as well as the transverse-momentum spectra, can be reasonably described by the JAM with a coalescence afterburner, suggesting a coalescence-based formation scenario for hyper-nuclei at this energy. The canonical thermal model reproduces the observed yield ratios but overpredicts the absolute hyper-nuclei yields.

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arXiv2026

Measurement of energy-level splitting from Charge-Symmetry Breaking in $A$ = 4 mirror hypernuclei

Breaking of fundamental symmetries is a ubiquitous phenomenon in physics, underlying the origin of mass and the emerging structure in the universe. The charge symmetry of $\Lambda$ hyperon-nucleon interactions can be probed through the difference in the $\Lambda$ binding energy ($B_{\Lambda}$) between mirror hypernuclei. In this paper, the $B_{\Lambda}$ of mirror hypernuclei with atomic mass number $A$ = 4, $\rm ^4_{\Lambda}H$ and $\rm ^4_{\Lambda}He$, are measured in Au+Au collisions at the center-of-mass energy of $\sqrt{s_{\rm NN}}$ = 3 GeV with the STAR experiment at RHIC. For the ground states, we obtain $B_{\Lambda}$($\rm ^4_{\Lambda}H$) = 2.24 $\pm$ 0.02 (stat.) $\pm$ 0.04 (syst.) MeV and $B_{\Lambda}$($\rm ^4_{\Lambda}He$) = 2.39 $\pm$ 0.05 (stat.) $\pm$ 0.05 (syst.) MeV, yielding a charge-symmetry breaking (CSB) effect at the level of 0.15 $\pm$ 0.05 (stat.) $\pm$ 0.04 (syst.) MeV. In combination with previous measurements of $\gamma$-ray transitions from their $1^+$ excited states, the CSB in excited states is determined to be $-$0.17 $\pm$ 0.05 (stat.) $\pm$ 0.04 (syst.) MeV. These measurements provide a precise determination of CSB in the hypernuclear system, and establish that the $\Lambda$ binding energy differences in ground and excited states are comparable in magnitude but opposite in sign, offering new insight to the CSB effect in $\Lambda$-nucleon interactions.

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arXiv2026

Observation of Strong $\phi$-meson Directed Flow at High Baryon Density

We report the first observation of a large directed flow ($v_1$) of $\phi$ mesons in mid-central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=3.0$-4.5 GeV, together with the $\sqrt{s_{\mathrm{NN}}}=7.7$ GeV collider-energy result for the collision-energy dependence, measured by the STAR experiment at RHIC. Despite its mesonic nature, the $\phi$-meson $v_{1}$ exhibits a magnitude comparable to that of protons and $\Lambda$ baryons, and is significantly larger (by a factor of $\gtrsim3$) than that of $K^0_S$ mesons at the lowest energies. The midrapidity slope $dv_1/dy$ shows a pronounced energy dependence similar to that observed for protons and $\Lambda$ baryons, in contrast to lighter mesons, in the high-baryon-density region. Comparisons with hadronic transport calculations indicate that the observed $\phi$-meson directed flow is consistent with production via high-mass baryon resonances and the collective motion of baryons influenced by baryonic mean-field interactions. Due to its long lifetime and relatively weak effective $\phi$-$N$ interaction, the $\phi$ meson can retain sensitivity to collective dynamics established during the dense baryonic stage of the collision. These results provide new experimental constraints on baryon-resonance production and strange-hadron transport dynamics in dense QCD matter.

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arXiv2026

Baryon-to-Meson Ratios in Jets from Au+Au and $p$+$p$ Collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV

Jet probes have been used extensively to gain insights into QGP properties, with substantial modifications to jet yields and internal structures seen across multiple measurements, compared against $p$+$p$ results. Despite apparent medium-induced changes to jet fragmentation patterns and strong modifications of particle production at intermediate momenta ($2.0 < p_{\rm{T}} < 5.0$ GeV/$c$) in heavy ion collisions, RHIC hadron-hadron correlation results indicate that jet-related baryon-to-meson ratios remain similar to those of $p$+$p$ measurements and are significantly different from those of the QGP bulk. To look for possible medium effects on jet fragments at RHIC, we employ jet-track correlation and particle identification to perform the first measurement of in-jet proton-to-pion yield ratios for charged-hadrons with $2.0 < p_{\rm{T}} < 5.0$ GeV/$c$. We present the first in-cone (within a radial distance of $R$ from the determined jet axis direction) baryon-to-meson yield ratios associated with reconstructed charged-particle jets from Au+Au and $p$+$p$ collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV using the STAR detector at RHIC. The measured in-jet ratios are found to be consistent within uncertainties between the two systems for the selected kinematic regime, despite significant differences between inclusive ratios for the same systems.

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arXiv2026

Measurements of jet quenching with semi-inclusive hadron-jet correlations in Ru+Ru and Zr+Zr collisions at $\sqrt{s_\mathrm{NN}}=200$ GeV

The STAR experiment at RHIC reports measurements of the semi-inclusive yield of charged-particle jets recoiling from high transverse momentum charged-hadron triggers in centrality-selected Ru+Ru and Zr+Zr collisions at the nucleon-nucleon center-of-mass energy of 200 GeV. The effects of jet quenching, arising from the interaction of jets with the quark-gluon plasma, are quantified by comparing trigger-normalized recoil yields in central and peripheral collisions. Suppression of the recoil yield in central collisions is observed, indicating medium-induced partonic energy loss due to quenching. The ratio of recoil jet yields for small and large resolution parameter is found to be suppressed in central relative to peripheral collisions, characteristic of medium-induced intra-jet broadening. The results are compared to similar measurements in smaller and larger collision systems, providing unique insight into the system-size dependence of jet quenching.

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arXiv2026

Elliptic Flow of Multi-strange Hadrons in Au+Au Collisions at $\sqrt{s_{NN}}$ = 7.7-19.6 GeV

Multi-strange hadrons ($\phi$, $\Xi$, and $\Omega$), owing to their small hadronic interaction cross sections, provide a sensitive probe of partonic collectivity with minimal distortion from late-stage hadronic rescattering. Using high-statistics data from the second phase of the STAR Beam Energy Scan program, we present precision measurements of elliptic flow ($v_2$) for multi-strange hadrons, together with other identified hadrons ($\pi^{\pm}, K^{\pm}$, $K_{S}^{0}$, $p$, and $\Lambda$) for comparison, in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7--19.6 GeV. Number-of-constituent-quark (NCQ) scaling is examined separately for particles and antiparticles. The NCQ-scaled $v_2$ of multi-strange hadrons follows the scaling observed for other identified species, with ratios relative to $K_{S}^{0}$ close to unity and exhibiting weak beam-energy dependence. The persistence of NCQ scaling for these weakly interacting probes provides strong evidence that collective flow is predominantly developed in the partonic phase, persisting down to $\sqrt{s_{NN}}$ = 7.7 GeV. The similar particle-antiparticle $v_2$ splittings observed for $p$, $\Lambda$, and $\Xi$, despite their markedly different hadronic cross sections, indicate that the splitting depends weakly on hadronic interaction strength. This suggests that late-stage hadronic interactions are subdominant and that the observed splitting primarily reflects dynamics established in the early, partonic stage.

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arXiv2026

Observation of Entanglement Enabled Spin-Interference in the Drell-S\"oding Process in Au+Au Ultraperipheral Collisions at RHIC

We report a measurement of the Drell-S\"oding $\pi^+ \pi^-$ production in Au + Au ultraperipheral collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}} = 200~\mathrm{GeV}$ using the STAR detector. For the first time, the Entanglement Enabled Spin-Interference (EESI) effect is observed in the Drell-S\"oding process through the amplitude $A_{2\Delta\phi}$ of the $\cos(2\Delta\phi)$ modulation. The measured $A_{2\Delta\phi}$ exhibits no significant dependence on the invariant mass $M_{\pi^+ \pi^-}$. An enhancement of three standard deviations is observed for the Drell-S\"oding process compared to $\rho^0$ photoproduction. Furthermore, we measure the $|t|$-dependence of the Drell-S\"oding process and $\rho^0$ photoproduction. The Drell-S\"oding spectrum falls more steeply with $|t|$ and exhibits diffractive structures shifted to lower $|t|$ compared to $\rho^0$ photoproduction, features that are not captured by theoretical calculations. These results provide new insights into the interplay between quantum interference and photon-nuclear interactions in ultra-peripheral heavy-ion collisions.

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arXiv2026

Collision Energy Dependence of Hypertriton Production in Au+Au Collisions at RHIC

The STAR Collaboration reports measurements of the collision energy dependence of hypertriton (${}^{3}_{\Lambda}$H) transverse momentum spectra and $p_{\rm T}$-integrated yields at mid-rapidity ($|y|<$0.5) in Au+Au collisions at 11 collision energies between 3.2 and 27\,GeV. The measured ${}^{3}_{\Lambda}$H yields and ${}^{3}_{\Lambda}$H/$\Lambda$ yields ratio in central collisions increase strongly with decreasing collision energy, and are a factor of $\sim$2 lower than thermal model predictions at this energy range. The mean $p_{\rm T}$ of ${}^{3}_{\Lambda}$H is lower than the Blast-Wave expectation using the freeze-out parameters from light hadrons. Furthermore, the observed double ratio $({}^{3}_{\Lambda}{\rm{H}}/\Lambda)/(t/p)$ maintains a constant value of $\sim$0.4 across the measured energy range. Within the coalescence framework, this ratio directly reflects the significantly suppressed formation probability of the weakly-bound hypertriton relative to the triton, which results from the weaker hyperon-nucleon interaction compared with the nucleon-nucleon interaction.

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arXiv2026

Elliptic flow of strange and multi-strange hadrons in isobar collisions at $\sqrt{s_{\mathrm {NN}}} = 200\mathrm{~GeV}$ at RHIC

We report a systematic measurement of elliptic flow ($v_{2}$) of $K_{s}^{0}$, $\Lambda$, $\overline{\Lambda}$, $\phi$, $\Xi^{-}$, $\overline{\Xi}^{+}$, and $\Omega^{-}$+$\overline{\Omega}^{+}$ at mid-rapidity ($|y| < 1.0$) for isobar, $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr, collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The transverse momentum ($p_\mathrm{T}$) dependence of $v_{2}$ is studied for various centrality classes. The number of constituent quark scaling of (multi-)strange hadrons is found to hold approximately within 20%, suggesting the development of partonic collectivity in isobar collisions similar to that observed in Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The average $v_{2}$ ratio shows $\sim$2% deviation from unity in central and mid-central collisions for strange hadrons, indicating a difference in nuclear structure and deformation between the isobars. The $v_{2}$ in isobaric collisions is compared to Cu+Cu, Au+Au, and U+U collisions at similar collision energies. We observe an increase in $v_{2}(p_\mathrm{T})$ with increasing system size. The difference in $v_{2}$ between the isobar and other collision systems increases with $p_\mathrm{T}$. The results are compared with a multi-phase transport model calculations with a deformed density profile to provide further insight into the nuclear structure of these isobars.

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arXiv2025

Measurement of Fifth- and Sixth-Order Fluctuations of (Net-)proton Number in Au+Au Collisions from Phase II of the Beam Energy Scan Program at RHIC

We report high-statistics measurements of fifth- and sixth-order factorial cumulants and cumulant ratios of (net-)proton multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}} = 7.7$--27 GeV, using data from the STAR experiment collected during the Beam Energy Scan Phase~II at RHIC. Protons and antiprotons are identified at midrapidity ($|y| < 0.5$) with transverse momentum $0.4 < p_T < 2.0$ GeV/$c$. The proton factorial cumulants $\kappa_4$, $\kappa_5$, and $\kappa_6$ increase with order but exhibit no sign alternation within current uncertainties, offering no evidence for a two-component structure in the proton multiplicity distribution, as might be expected near a first-order phase transition. The cumulant ratios $C_{5}/C_{1}$ and $C_{6}/C_{2}$ fluctuate around zero in collisions at 0--40\% centrality. The results are consistent with both the negative predictions from lattice QCD (LQCD) and the positive trends obtained from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. At $\sqrt{s_{NN}} \gtrsim 27$ GeV, the $C_4/C_2$ and $C_5/C_1$ results are compatible with predictions from lattice QCD, functional renormalization group (FRG), and hadron resonance gas (HRG) models, while UrQMD describes the data better at lower energies. These measurements place constraints on baryon number fluctuations and offer valuable insights into the QCD phase structure.

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arXiv2025

Evidence of Spin-Interference Effects in Exclusive $J/\psi \to e^+e^-$ Photoproduction in Ultraperipheral Heavy-Ion Collisions

We report the first evidence of spin interference in exclusive $J/\psi \to e^+e^-$ photoproduction in ultraperipheral heavy-ion collisions at STAR at $\sqrt{s_{NN}} = 200$~GeV. In Au+Au collisions, a negative $\cos(2\phi)$ modulation is found for $p_T < 120$~MeV/$c$ with a significance of $3.2\sigma$, while the isobar data (Ru+Ru, Zr+Zr) show a consistent negative modulation with a significance of $1.9\sigma$, opposite in sign to that in $\rho^{0}\!\to\!\pi^+\pi^-$ photoproduction. This establishes for the first time that the interference sign is controlled by the spin structure of the final-state daughters, resolving the ambiguity present in the all-boson $\rho^0$ channel. The compact $J/\psi$ probes gluon distributions at perturbative scales, resulting in a weaker modulation and providing stringent constraints on Color Glass Condensate calculations. These findings demonstrate that spin-dependent interference in heavy vector mesons provides a new, experimentally accessible handle on gluon structure beyond traditional cross-section measurements.

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arXiv2025

Charged-Particle Multiplicity Dependence of Net-Proton Cumulants in Zr+Zr and Ru+Ru Collisions at $\sqrt{s_{NN}}$ = 200 GeV

We present measurements of cumulants of event-by-event net-proton distribution at mid-rapidity and their ratios up to the sixth order as a function of charged-particle multiplicity in Zr+Zr and Ru+Ru(isobars) collisions at a nucleon-nucleon center-of-mass energy ($\sqrt{s_{NN}}$) of 200 GeV. The data are collected from the STAR experiment with a total of two billion events recorded for each collision system. The measurements are compared with those obtained from p+p and Au+Au collision systems at the same center-of-mass energy. The higher-order cumulant ratios ($C_4/C_2$, $C_5/C_1$, and $C_6/C_2$) show an overall decreasing trend as a function of the charged-particle multiplicity across systems. The isobar results align with the Au+Au trends within uncertainties. The observations are compared with calculations from Lattice Gauge Theory (LGT) that include a quark-hadron crossover. The systematic behavior of the higher-order cumulant ratios shows that, overall, they progressively approach LGT predictions with increasing multiplicity within uncertainties. This could imply that the medium created in these heavy-ion collisions gradually evolves into thermalized QCD matter undergoing a crossover transition with multiplicity.

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arXiv2025

Measurement of inclusive $J/\psi$ production in Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 54.4$ GeV at STAR

This article presents measurements of inclusive $J/\psi$ production at midrapidity ($\left|y\right| <$ 1.0) in Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 54.4$ GeV with the STAR detector at the Relativistic Heavy Ion Collider. A suppression of the $J/\psi$ yield, quantified using the nuclear modification factors ($R_{\mathrm{AA}}$, $R_{\mathrm{CP}}$), is observed with respect to the scaled production in $p$+$p$ collisions. The dependence of $R_{\mathrm{AA}}$ on collision centrality and $J/\psi$ transverse momentum is measured with improved precision compared to previous measurements at 39 and 62.4 GeV, while the centrality dependence of $R_{\mathrm{CP}}$ is measured and compared to the same results at 39, 62.4, and 200 GeV. In central collisions, no significant collision energy dependence of $R_{\mathrm{AA}}$ is found within uncertainties for collision energies between 17.3 and 200 GeV. Two transport model calculations that include dissociation and regeneration contributions are consistent with the experimental results within uncertainties. Although no significant collision energy dependence of the $J/\psi$ suppression in high energy heavy-ion collisions up to $\sqrt{s_\mathrm{NN}} = 200$ GeV is observed within uncertainties, the newly measured results at 54.4 GeV Au+Au collisions provide additional constraints on theoretical calculations of the hot medium evolution and cold nuclear matter effects.

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arXiv2025

Measuring spin correlation between quarks during QCD confinement

The vacuum is now understood to possess a rich and complex structure, characterized by fluctuating energy fields and a condensate of virtual quark-antiquark pairs. The spontaneous breaking of the approximate chiral symmetry, signaled by the nonvanishing quark condensate $\langle q\bar{q}\rangle$, is dynamically generated through topologically nontrivial gauge configurations such as instantons. The precise mechanism linking the chiral symmetry breaking to the mass generation associated with quark confinement remains a profound open question in Quantum Chromodynamics (QCD) - the fundamental theory of strong interaction. High energy proton-proton collisions could liberate virtual quark-antiquark pairs from the vacuum that subsequently undergo confinement to form hadrons, whose properties could serve as probes into QCD confinement and the quark condensate. Here, we report evidence of spin correlations in $\Lambda\bar{\Lambda}$ hyperon pairs inherited from spin-correlated strange quark-antiquark virtual pairs. Measurements by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory reveal a relative polarization signal of $(18 \pm 4)\%$ that links the virtual spin-correlated quark pairs from the QCD vacuum to their final-state hadron counterparts. Crucially, this correlation vanishes when the hyperon pairs are widely separated in angle, consistent with the decoherence of the quantum system. Our findings provide a new experimental paradigm for exploring the dynamics and interplay of quark confinement and entanglement.

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arXiv2025

Charge Separation Measurements in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7--200 GeV in Search of the Chiral Magnetic Effect

The chiral magnetic effect in heavy-ion collisions predicts a charge separation signal along a magnetic field, which indicates local $P$ and $CP$ violations in the quark-gluon plasma. We report measurements of electric charge separation signals perpendicular to the spectator event plane in Au+Au collisions using high-statistics data from RHIC Beam Energy Scan II and top-energy runs. A novel event shape selection method is employed to suppress the flow-induced background. The residual charge separation signals near the zero-flow limit are positive in Au+Au collisions within the 20\%--50\% centrality range, with significance levels of $2.6\sigma$, $3.1\sigma$, and $3.3\sigma$ at $\sqrt{s_{NN}} =$ 11.5, 14.6, and 19.6 GeV, respectively. At other beam energies, the signals are either statistically limited or consistent with zero.

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arXiv2025

Search for the chiral magnetic effect through beam energy dependence of charge separation using event shape selection

High-energy, heavy-ion collisions can create local domains of chirality-imbalanced quarks, reflecting the topological features of quantum chromodynamics. The chiral magnetic effect (CME) predicts an electric charge separation of quarks in such topological domains along the magnetic field ($\vec{B}$) generated by the passing of two high-$Z$ nuclei. We use a correlation observable $\Delta\gamma^{112}$ between charged meson pairs to detect the CME-induced charge separation and a novel event shape selection (ESS) method to mitigate the background effects related to elliptic flow ($v_2$). The ESS method classifies events based on the emission pattern of final-state particles and determines $\Delta\gamma^{112}_{\rm ESS}$ from the zero-flow limit. We reconstruct the $\vec{B}$ field direction from the spectator nucleons, which minimizes backgrounds unrelated to the collective motion of the system. In this work, we report the measurements of $\Delta\gamma^{112}$ and a background indicator $\Delta\gamma^{132}$ in Au+Au collisions from the RHIC Beam Energy Scan phase II and at the top RHIC energy. After background suppression, $\Delta\gamma^{132}_{\rm ESS}$ aligns with zero, and $\Delta\gamma^{112}_{\rm ESS}$ is reduced to no more than 20\% of $\Delta\gamma^{112}$. We observe a finite residual charge separation with $2.6\sigma$, $3.1\sigma$, and $3.3\sigma$ significance in the 20\%--50\% centrality range of Au+Au collisions at 11.5, 14.6, and 19.6 GeV. The results at 17.3 and 27 GeV also show positive values but with a lower significance of $1.3\sigma$ and $1.1\sigma$, respectively. The corresponding $\Delta\gamma^{112}_{\rm ESS}$ values at 7.7, 9.2, and 200 GeV are consistent with zero within uncertainties.

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