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Anderson, D. M.

Publications and source records attributed to Anderson, D. M..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Semi-inclusive direct photon + jet and šœ‹ 0 + jet correlations measured in š‘ + š‘ and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200GeV

The STAR experiment at RHIC reports new measurements of jet quenching based on the semi- inclusive distribution of charged-particle jets recoiling from direct photon (Ī³ dir ) and neutral pion (Ļ€ 0 ) triggers in pp and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for triggers in the range 9 < $E$$^{trig}_{T}$ < 20 GeV. The datasets have integrated luminosities of 3.9nb āˆ’1 for Au + Au and 23pb āˆ’1 for š‘š‘ collisions. Jets are reconstructed using the anti-š‘˜ š‘‡ algorithm with resolution parameters š‘… = 0.2 and 0.5. The large uncorrelated jet background in central Au + Au collisions is corrected using a mixed-event approach, which enables precise charged-particle jet measurements at low transverse momentum š‘$^{ch}_{š‘‡,jet}$ and large š‘…. Recoil-jet distributions are reported in the range š‘$^{ch}_{š‘‡,jet}$ < 25 GeV/š‘. Comparison of the distributions measured in š‘š‘ and Au + Au collisions reveals strong medium-induced jet yield suppression for š‘… = 0.2 with markedly less suppression for š‘… = 0.5. Comparison is also made to theoretical models incorporating jet quenching. Furthermore, these data provide new insight into the mechanisms underlying jet quenching and the angular dependence of medium-induced jet-energy transport and provide new constraints on modeling such effects.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2024

Longitudinal and transverse spin transfer to $Ī›$ and $\overline{Ī›}$ hyperons in polarized $p$ + $p$ collisions at āˆšs = 200 GeV

The longitudinal and transverse spin transfers to Ī› ($\overline{Ī›}$) hyperons in polarized proton-proton collisions are expected to be sensitive to the helicity and transversity distributions, respectively, of (anti)strange quarks in the proton, and to the corresponding polarized fragmentation functions. We report improved measurements of the longitudinal spin transfer coefficient, D LL , and the transverse spin transfer coefficient, D TT , to Ī› and $\overline{Ī›}$ in polarized proton-proton collisions at āˆšs = 200 GeV by the STAR experiment at RHIC. The dataset includes longitudinally polarized proton-proton collisions with an integrated luminosity of 52 pb ā€“1 , and transversely polarized proton-proton collisions with a similar integrated luminosity. Both datasets have about twice the statistics of previous results and cover a kinematic range of |Ī· Ī› ($\overline{Ī›}$) | < 1.2 and transverse momentum p T , Ī›($\overline{Ī›}$) up to 8GeV/c. We also report the first measurements of the hyperon spin transfer coefficients D LL and D TT as a function of the fractional jet momentum z carried by the hyperon, which can provide more direct constraints on the polarized fragmentation functions

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSā†—
DOE OSTI2023

Energy dependence of intermittency for charged hadrons in Au+Au collisions at RHIC

Density fluctuations near the QCD critical point can be probed via an intermittency analysis in relativistic heavy-ion collisions. We report the first measurement of intermittency in Au+Au collisions at $\sqrt{s{NN}}$ = 7.7-200 GeV measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The scaled factorial moments of identified charged hadrons are analyzed at mid-rapidity and within the transverse momentum phase space. We observe a power-law behavior of scaled factorial moments in Au+Au collisions and a decrease in the extracted scaling exponent (Ī½) from peripheral to central collisions. The Ī½ is consistent with a constant for different collisions energies in the mid-central (10-40%) collisions. Moreover, the Ī½ in the 0-5% most central Au+Au collisions exhibits a non-monotonic energy dependence that reaches a minimum around $\sqrt{s{NN}}$ = 27 GeV. The physics implications on the QCD phase structure are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Elliptic flow of heavy-flavor decay electrons in Au+Au collisions at s NN = 27 and 54.4 GeV at RHIC

We report on new measurements of elliptic flow (v 2 ) of electrons from heavy-flavor hadron decays at mid-rapidity (|y| < 0.8) in Au+Au collisions at $\sqrt{s{NN}}$ = 27 and 54.4 GeV from the STAR experiment. Heavy-flavor decay electrons (eHF) in Au+Au collisions at $\sqrt{s{NN}}$ = 54.4 GeV exhibit a non-zero v 2 in the transverse momentum (p T ) region of p T < 2 GeV/c with the magnitude comparable to that at $\sqrt{s{NN}}$=200 GeV. The measured e HF v 2 at 54.4 GeV is also consistent with the expectation of their parent charm hadron v 2 following number-of-constituent-quark scaling as other light and strange flavor hadrons at this energy. These suggest that charm quarks gain significant collectivity through the evolution of the QCD medium and may reach local thermal equilibrium in Au+Au collisions at $\sqrt{s{NN}}$=54.4 GeV. The measured e HF v 2 in Au+Au collisions at $\sqrt{s{NN}}$ = 27 GeV is consistent with zero within large uncertainties. The energy dependence of v 2 for different flavor particles (Ļ€,Ī¦,D 0 /e HF ) shows an indication of quark mass hierarchy in reaching thermalization in high-energy nuclear collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Global polarization of Ī› and $\overline{Ī›}$ hyperons in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6 and 27 GeV

In relativistic heavy-ion collisions, a global spin polarization, š‘ƒ H , of Ī› and $\overline{Ī›}$ hyperons along the direction of the system angular momentum was discovered and measured across a broad range of collision energies and demonstrated a trend of increasing š‘ƒ H with decreasing $\sqrt{s_{NN}}$. A splitting between Ī› and $\overline{Ī›}$ polarization may be possible due to their different magnetic moments in a late-stage magnetic field sustained by the quark-gluon plasma which is formed in the collision. The results presented in this study find no significant splitting at the collision energies of $\sqrt{s_{NN}}$ = 19.6 and 27 GeV in the BNL Relativistic Heavy Ion Collisions Beam Energy Scan Phase II using the STAR detector, with an upper limit of š‘ƒ $\overline{Ī›}$ ā€“ š‘ƒ Ī› < 0.24% and š‘ƒ $\overline{Ī›}$ ā€“ š‘ƒ Ī› < 0.35%, respectively, at a 95% confidence level. We derive an upper limit on the naive extraction of the late-stage magnetic field of šµ < 9.4 Ɨ 10 12 T and šµ < 1.4 Ɨ 10 13 T at $\sqrt{s_{NN}}$ = 19.6 and 27 GeV, respectively, although more thorough derivations are needed. Differential measurements of š‘ƒ H were performed with respect to collision centrality, transverse momentum, and rapidity. With our current acceptance of |š‘¦| < 1 and uncertainties, we observe no dependence on transverse momentum and rapidity in this analysis. Furthermore, these results challenge multiple existing model calculations following a variety of different assumptions which have each predicted a strong dependence on rapidity in this collision-energy range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Event-by-event correlations between Ī› ( Ī› ĀÆ ) hyperon global polarization and handedness with charged hadron azimuthal separation in Au + Au collisions at s N N = 27 GeV from STAR

Global polarizations (P) of Ī› (Ī›ĀÆ) hyperons have been observed in non-central heavy-ion collisions. The strong magnetic field primarily created by the spectator protons in such collisions would split the Ī› and Ī›ĀÆ global polarizations (Ī”P=P Ī› ā€“P Ī› ĀÆ<0). Additionally, quantum chromodynamics (QCD) predicts topological charge fluctuations in vacuum, resulting in a chirality imbalance or parity violation in a local domain. This would give rise to an imbalance (Ī”n = N L ā€“N R /< N L +N R > ā‰ 0) between left- and right-handed Ī› (Ī›ĀÆ) as well as a charge separation along the magnetic field, referred to as the chiral magnetic effect (CME). This charge separation can be characterized by the parity-even azimuthal correlator (Ī”Ī³) and parity-odd azimuthal harmonic observable (Ī”a 1 ). Measurements of Ī”P, Ī”Ī³, and Ī”a 1 have not led to definitive conclusions concerning the CME or the magnetic field, and Ī”n has not been measured previously. Correlations among these observables may reveal new insights. Furthermore, this paper reports measurements of correlation between Ī”n and Ī”a 1 , which is sensitive to chirality fluctuations, and correlation between Ī”P and Ī”Ī³ sensitive to magnetic field in Au+Au collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Search for the chiral magnetic wave using anisotropic flow of identified particles at energies available at the BNL Relativistic Heavy Ion Collider

The chiral magnetic wave (CMW) has been theorized to propagate in the deconfined nuclear medium formed in high-energy heavy-ion collisions, and to cause a difference in elliptic flow (v 2 ) between negatively and positively charged hadrons. Experimental data consistent with the CMW have been reported by the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC), based on the charge asymmetry dependence of the pion v 2 from Au+Au collisions at $\sqrt{s_{NN}}$ = 27 to 200 GeV. In this comprehensive study, we present the STAR measurements of elliptic flow and triangular flow of charged pions, along with the v 2 of charged kaons and protons, as a function of charge asymmetry in Au+Au collisions at $\sqrt{s_{NN}}$ = 27, 39, 62.4 and 200 GeV. The slope parameters extracted from the linear dependence of the v2 difference on charge asymmetry for different particle species are reported and compared in different centrality intervals. In addition, the slopes of v 2 for charged pions in small systems, i.e., p+Au and d+Au at $\sqrt{s_{NN}}$ = 200 GeV, are also presented and compared with those in large systems, i.e., Au+Au at $\sqrt{s_{NN}}$ = 200 GeV and U+U at 193 GeV. Our results provide new insights for the possible existence of the CMW, and further constrain the background contributions in heavy-ion collisions at RHIC energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Measurement of electrons from open heavy-flavor hadron decays in Au+Au collisions at $ \sqrt{s_{\textrm{NN}}} $ = 200 GeV with the STAR detector

We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity (|y| < 0.7) in Au+Au collisions at $ \sqrt{s_{\textrm{NN}}} $ = 200 GeV. Invariant yields of HFEs are measured for the transverse momentum range of 3.5 < p T < 9 GeV/c in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in p + p collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Measurements of the Elliptic and Triangular Azimuthal Anisotropies in Central He 3 + Au , d + Au and p + Au Collisions at s N N = 200 GeV

The elliptic (v 2 ) and triangular (v 3 ) azimuthal anisotropy coefficients in central 3He + Au, d + Au, and p + Au collisions at $\sqrt{S_{NN}}$ = 200 GeV are measured as a function of transverse momentum (P T ) at midrapidity (|n| < 0.9) via the azimuthal angular correlation between two particles both at |n| < 0.9 while the v 2 (P T ) values depend on the colliding systems, the v 3 (P T ) values are system independent within the uncertainties, suggesting an influence on eccentricity from subnucleonic fluctuations in these small-sized systems. Furthermore, these results also provide stringent constraints for the hydrodynamic modeling of these systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Measurements of dielectron production in Au + Au collisions at s N N = 27 , 39, and 62.4 GeV from the STAR experiment

We report systematic measurements of dielectron (e + e ā€“ ) invariant-mass M ee spectra at midrapidity in Au + Au collisions at s N N = 27 = 27, 39, and 62.4 GeV taken with the STAR detector at the Relativistic Heavy Ion Collider. For all energies studied, a significant excess yield of dielectrons is observed in the low-mass region ( 0.40 < M ee < 0.75 MeV / c 2 ) compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the Ļ -meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for Au + Au collisions at midrapidity ( |y ee | < 1) in the 0ā€“80% centrality bin for each collision energy. The integrated excess yields for 0.4 < M ee < 0.75 GeV / c 2 , normalized by the charged particle multiplicity at midrapidity, are compared with previously published measurements for Au + Au at s N N = 27 = 19.6 and 200 GeV. Models that include an in-medium broadening of the Ļ -meson spectral function consistently describe the observed excess. Furthermore, the normalized excess yields in the low-mass region show no significant collision energy dependence. The data, however, are consistent with model calculations that demonstrate a modest energy dependence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Observation of Directed Flow of Hypernuclei $^3_Ī›\text{H}$ and $^4_Ī›\text{H}$ in $\sqrt{s_{\text{NN}}}$ = 3 GeV Au + Au Collisions at RHIC

We report here the first observation of directed flow ($v_1$) of the hypernuclei $^3_Ī›\text{H}$ and $^4_Ī›\text{H}$ in mid-central Au + Au collisions at $\sqrt{s_{\text{NN}}}$ = 3 GeV at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From 165 Ɨ 10 6 events in 5%ā€“40% centrality, about 8400 $^3_Ī›\text{H}$ and 5200 $^4_Ī›\text{H}$ candidates are reconstructed through two- and three-body decay channels. In this work, 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 $^3_Ī›\text{H}$ and $^4_Ī›\text{H}$ follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in the 3 GeV Au + Au collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Beam Energy Dependence of Triton Production and Yield Ratio $N_t \times N_p / N^2_d$ in Au+Au Collisions at RHIC

We report the triton (t) production in midrapidity (|y| < 0.5) Au + Au collisions at $\sqrt{s_{NN}} = 7.7-200$ GeV measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider. The nuclear compound yield ratio ($N_t \times N_p / N^2_d$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($dN_{ch}/dĪ·$) and follows a scaling behavior. The $dN_{ch}/dĪ·$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0%-10% most central collisions at 19.6 and 27 GeV, with a significance of 2.3Ļƒ and 3.4Ļƒ, respectively, giving a combined significance of 4.1Ļƒ. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_T$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Beam energy dependence of the linear and mode-coupled flow harmonics in Au+Au collisions

The linear and mode-coupled contributions to higher-order anisotropic flow are presented for Au+Au collisions at āˆš S NN = 27, 39, 54.4, and 200 GeV and compared to similar measurements for Pb+Pb collisions at the Large Hadron Collider (LHC). The coefficients and the flow harmonics' correlations, which characterize the linear and mode-coupled response to the lower-order anisotropies, indicate a beam energy dependence consistent with an influence from the specific shear viscosity (Ī·/s). In contrast, the dimensionless coefficients, mode-coupled response coefficients, and normalized symmetric cumulants are approximately beam-energy independent, consistent with a significant role from initial-state effects. These measurements could provide unique supplemental constraints to (i) distinguish between different initial-state models and (ii) delineate the temperature (T) and baryon chemical potential (Ī¼ B ) dependence of the specific shear viscosity Ī·/s(T, Ī¼ B ).

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

$K^{*0}$ production in $\text{Au} \times \text{Au}$ collisions at $\sqrt{s_{NN}} = 7.7$, 11.5, 14.5, 19.6, 27, and 39 GeV from the RHIC beam energy scan

We report the measurement of K *0 meson at midrapidity (|y|< 1.0) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse momentum of K *0 are presented as functions of collision centrality and beam energy. The K *0 /K yield ratios are presented for different collision centrality intervals and beam energies. The K *0 /K ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and p+p). The K *0 /K ratio follows a similar centrality dependence to that observed in previous RHIC and LHC measurements. The data favor the scenario of the dominance of hadronic re-scattering over regeneration for K *0 production in the hadronic phase of the medium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Measurement of Sequential Ļ’ Suppression in Au + Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR Experiment

We report on measurements of sequential Ļ’ suppression in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector at the Relativistic Heavy Ion Collider (RHIC) through both the dielectron and dimuon decay channels. In the 0%ā€“60% centrality class, the nuclear modification factors (š‘… š“ā¢š“ ), which quantify the level of yield suppression in heavy-ion collisions compared to š‘ + š‘ collisions, for Ļ’ā”(1ā¢š‘†) and Ļ’ā”(2ā¢š‘†) are 0.40 Ā± 0.03ā¢(stat) Ā± 0.03ā¢(sys) Ā± 0.09ā¢(norm) and 0.26 Ā± 0.08ā¢(stat) Ā± 0.02ā¢(sys) Ā± 0.06ā¢(norm), respectively, while the upper limit of the Ļ’ā”(3ā¢š‘†) š‘… š“ā¢š“ is 0.17 at a 95% confidence level. This provides experimental evidence that the Ļ’ā”(3ā¢š‘†) is significantly more suppressed than the Ļ’ā”(1ā¢š‘†) at RHIC. The level of suppression for Ļ’ā”(1ā¢š‘†) is comparable to that observed at the much higher collision energy at the Large Hadron Collider. Furthermore, these results point to the creation of a medium at RHIC whose temperature is sufficiently high to strongly suppress excited Ļ’ states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—
DOE OSTI2023

Beam Energy Dependence of Fifth- and Sixth-Order Net-Proton Number Fluctuations in Au + Au Collisions at RHIC

We report the beam energy and collision centrality dependence of fifth and sixth order cumulants (C 5 , C 6 ) and factorial cumulants (Īŗ 5 , Īŗ 6 ) of net-proton and proton distributions, from $\sqrt{s_{NN}}$=3-200 GeV Au+Au collisions at RHIC. The net-proton cumulant ratios generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at $\sqrt{s_{NN}}$ = 3 GeV. C 6 /C 2 for 0-40\% centrality collisions is increasingly negative with decreasing $\sqrt{s_{NN}}$, while it is positive for the lowest $\sqrt{s_{NN}}$ studied. These observed negative signs are consistent with QCD calculations (at baryon chemical potential, Ī¼ B ā‰¤ 110 MeV) that include a crossover quark-hadron transition. In addition, for $\sqrt{s_{NN}}$ā‰„ 11.5 GeV, the measured proton Īŗ n , within uncertainties, does not support the two-component shape of proton distributions that would be expected from a first-order phase transition. Taken in combination, the hyper-order proton number fluctuations suggest that the structure of QCD matter at high baryon density, Ī¼ B ~750 MeV ($\sqrt{s_{NN}}$ = 3 GeV) is starkly different from those at vanishing Ī¼ B ~20MeV ($\sqrt{s_{NN}}$ = 200 GeV and higher).

73 NUCLEAR PHYSICS AND RADIATION PHYSICSā†—