GeV Au Research Articles

Density changes in amorphous silicon induced by swift heavy ions

Pure and gold-doped amorphous silicon membranes were irradiated with swift heavy ions (75 MeV Ag or 1.1 GeV Au ions) and studied using small-angle x-ray scattering. The samples that were irradiated with 1.1 GeV Au ions produced a scattering pattern consistent with core-shell-type ion tracks of 2.0 $\ifmmode\pm\else\textpm\fi{}$ 0.1 nm (core) and 7.0 $\ifmmode\pm\else\textpm\fi{}$ 0.3 nm (total) radius irrespective of gold doping, consistent with radii previously observed [9]. The density in the core is nearly 4% different from that of the surrounding material. The entire track (core $+$ shell) is slightly less dense than the surrounding material, yielding an expansion or hammering constant $A$ of $0.036\ifmmode\pm\else\textpm\fi{}0.003$ ${\mathrm{nm}}^{2}$ per ion track, consistent with the macroscopic ``hammering'' deformation. No tracks were found in samples irradiated with 75 MeV Ag ions, and no signature specific to the gold impurity doping could be observed.

Measurements of $\phi$ meson and $\Xi^-$ hyperon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV from STAR experiment

In this proceedings, we present our first measurements of \phiϕ meson and \Xi^-Ξ− hyperon production in Au+Au collisions at \sqrt{s_{NN}}sNN = 3 GeV. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.

Heavy ion irradiation induced phase transitions and their impact on the switching behavior of ferroelectric hafnia

The discovery of ferroelectric hafnium oxide enabled a variety of non-volatile memory devices, like ferroelectric tunnel junctions or field-effect transistors. Reliable application of hafnium oxide based electronics in space or other high-dose environments requires an understanding of how these devices respond to highly ionizing radiation. Here, the effect of 1.6 GeV Au ion irradiation on these devices is explored, revealing a reversible phase transition, as well as a grain fragmentation process. The collected data demonstrate that non-volatile memory devices based on ferroelectric hafnia layers are ideal for applications where excellent radiation hardness is mandatory.

Structural stability of REE-PO4 (REE = Sm,Tb) under swift heavy ion irradiation

Rare earth element (REE) phosphates are an attractive host matrix for long-lived radionuclides from nuclear waste because of the radiation tolerance exhibited by naturally occurring REE phosphate specimens. Here we show that SmPO4 (monazite structure) and TbPO4 (xenotime structure) exhibit a similar amorphization response to swift heavy ion irradiation despite different starting structures. SmPO4 and TbPO4 were irradiated with 1.1 GeV Au ions and analyzed using synchrotron-based X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The radiation response of the phosphates was evaluated by extracting the amorphous fraction at each irradiation fluence, and a single-impact model was used to determine the amorphous cross section and track diameter. Amorphization within individual ion tracks was confirmed using head-on TEM imaging, and the amorphous track size agreed with the value deduced by XRD analysis. Raman measurements were performed to qualitatively confirm the ion-induced crystalline-to-amorphous transformation which proceeds similarly for both phosphates.

Disappearance of partonic collectivity in [formula omitted] GeV Au+Au collisions at RHIC

We report on the measurements of directed flow v1 and elliptic flow v2 for hadrons (π±, K±, KS0, p, ϕ, Λ and Ξ−) from Au+Au collisions at sNN=3GeV and v2 for (π±, K±, p and p‾) at 27 and 54.4GeV with the STAR experiment. While at the two higher energy midcentral collisions the number-of-constituent-quark (NCQ) scaling holds, at 3GeV the v2 at midrapidity is negative for all hadrons and the NCQ scaling is absent. In addition, the v1 slopes at midrapidity for almost all observed hadrons are found to be positive, implying dominant repulsive baryonic interactions. The features of negative v2 and positive v1 slope at 3GeV can be reproduced with a baryonic mean-field in transport model calculations. These results imply that the medium in such collisions is likely characterized by baryonic interactions.

Event-by-Event Investigation of the Two-Particle Source Function in Heavy-Ion Collisions with EPOS.

Exploring the shape of the pair-source function for particles such as pions or kaons has been an important goal of heavy-ion physics, and substantial effort has been made in order to understand the underlying physics behind the experimental observations of non-Gaussian behavior. In experiments, since no direct measurement of the source function is possible, quantum-statistical momentum correlations are utilized to gain information about the space-time geometry of the particle emitting source. Event generators, such as EPOS, however, provide direct access to the freeze-out coordinates of final state particles, and thus the source function can be constructed and investigated. The EPOS model is a sophisticated hybrid model where the initial stage evolution of the system is governed by Parton-Based Gribov–Regge theory, and subsequently a hydrodynamic evolution is utilized, followed by hadronization and hadron dynamics. EPOS has already proven to be successful in describing several different experimental observations for systems characterized by baryon chemical potential close to zero, but so far the source shape has not been explored in detail. In this paper we discuss an event-by-event analysis of the two-particle source function in = 200 GeV Au+Au collisions generated by the EPOS model. We find that when utilizing all stages of the model, Lévy-shaped distributions (unlike Gaussian distributions) provide a good description of the source shape in the individual events. Hence it is clear that it is not the event averaging that creates the non-Gaussian features in the pair distributions. Based on this observation, we determine Lévy-parameters of the source as a function of event centrality and particle momentum.

Light nuclei collectivity from [formula omitted] GeV Au+Au collisions at RHIC

In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and dominance of baryonic interactions is found for identified hadron collective flow measurements in sNN = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in sNN = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.

Measurements of electrons from heavy-flavor hadron decays in 27, 54.4, and 200 GeV Au+Au collisions in STAR

In these proceedings, we present the measurements of nuclear modification factors for electrons from open charm (c→e) and bottom hadron decays (b→e) at mid-rapidity region in Au+Au collisions at √SNN = 200 GeV. The significance of the difference in nuclear modification factors between b→e and c→e is ≥ 3σ. We also present the measurements of the elliptic flow (v2) of inclusive heavy-flavor hadron decayed electrons (HFE) in Au+Au collisions at √SNN = 27 and 54.4 GeV. The results show non-zero HFE v2 in 54.4 GeV Au+Au collisions and a hint of smaller HFE v2 in 27 GeV Au+Au collisions than those at 54.4 and 200 GeV.

Recent studies on hypernuclei lifetimes from STAR

The hyperon-nucleon (Y-N) interaction is an essential ingredient in the description of the equation-of-state of high-baryon-density matter. Light hypernuclei (A = 3, 4), being simple Y-N bound states, serve as cornerstones of our understanding of the Y-N interaction. Thus, precise measurements of their lifetimes are important, as they provide stringent tests to hyperon-nucleon interaction models. The yields of light hypernuclei are expected to increase from high to low energy heavy-ion collisions due to the increase in baryon density. As a result, the STAR Beam Energy Scan II program, which spans an energy range of √sNN = 3.0 − 27.0 GeV, is particularly suited for hypernuclei studies. In these proceedings, recent results on the lifetimes of light hypernuclei (3ΛH, 4ΛH, 4ΛHe) measured in √sNN = 3.0 and 7.2 GeV Au+Au collisions are presented. The relative branching ratio R3 of the 3ΛH is intimately related to its lifetime. A new R3 measurement using data from √sNN = 3.0 GeV Au+Au collisions is reported. These results will be compared to previous measurements and theoretical calculations, and the physics implications will be discussed.

Light and strange hadron production and anisotropic flow measurement in Au+Au collisions at √SNN = 3 GeV from STAR

In this proceeding, we present on our first measurements of identified particle (π, K, p, Ks0, Λ, ϕ, Ξ−) production and anisotropic flow (υ1, υ2) in Au+Au collisions at √SNN = 3 GeV. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.

NCQ scaling of f0(980) elliptic flow in 200 GeV Au+Au collisions by STAR and its constituent quark content

Searching for exotic state particles and studying their properties have furthered our understanding of quantum chromodynamics (QCD). The f0(980) resonance is an exotic state with relatively high production rate in relativistic heavy-ion collisions, decaying primarily into ππ. Currently the structure and quark content of the f0(980) are unknown with several predictions from theory being a qq¯ state, a qqq¯q¯ state, a KK¯ molecule state, or a gluonium state. We report the first f0(980) elliptic flow (v2) measurement from 200 GeV Au+Au collisions at STAR. The transverse momentum dependence of v2 is examined and compared to those of other hadrons (baryons and mesons). The empirical number of constituent quark (NCQ) scaling is used to investigate the constituent quark content of f0(980), which may potentially address an important question in QCD.

Measurement of the Sixth-Order Cumulant of Net-Proton Multiplicity Distributions in Au+Au Collisions at sqrt[s_{NN}]=27, 54.4, and 200GeV at RHIC.

According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region μ_{B}≤T_{c}. In this range the ratio, C_{6}/C_{2}, of net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton C_{6}/C_{2} from 27, 54.4, and 200GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in (p_{T}, y) are analyzed. While for 27 and 54.4GeV collisions the C_{6}/C_{2} values are close to zero within uncertainties, it is observed that for 200GeV collisions, the C_{6}/C_{2} ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.

Ion tracks in ultrathin polymer films: The role of the substrate

Surface damage produced by single MeV-GeV heavy ions impacting ultrathin polymer films has been shown to be weaker than those observed under bulk (thick film) conditions. The decrease in damage efficiency has been attributed to the suppression of long-range effects arising from excited atoms lying deeply in the solid. This raises the possibility that the substrate of the films itself is relevant to the radiation effects seen at the top surface. Here, the role of the substrate on cratering induced by individual 1.1 GeV Au ions in ultrathin poly(methyl methacrylate) (PMMA) layers is investigated. Materials of different thermal and electrical properties (Si, SiO2, and Au) are used as substrates to deposit PMMA thin films of various thicknesses from ∼1 to ∼300 nm. We show that in films thinner than ∼40 nm craters are modulated by the underlying substrate to a degree that depends on the transport properties of the medium. Crater size in ultrathin films deposited on the insulating SiO2 is larger than in similar films deposited on the conducting Au layer. This is consistent with an inefficient coupling of the electronic excitation energy to the atomic cores in metals. On the other hand, the damage on films deposited on SiO2 is not very different from the Si substrate with a native oxide layer, suggesting, in addition, poor energy transmission across the film/substrate interface. The experimental observations are also compared to calculations from an analytical model based on energy addition and transport from the excited ion track, which describe only partially the results.

The sixth order cumulant of net-proton number in Binomial distribution at = 200 GeV * *Supported by the postdoctral science and technology project of Hubei Province (2018Z27) and the Fundamental Research Funds for the Central Universities (CCNU19ZN019)

It is proposed that ratios of the sixth order to the second order cumulant ( ) of conserved quantities are sensitive to the chiral crossover transition. Recently, the negative was obtained in both theoretical Lattice QCD and experiments at = 200 GeV. In this study, we investigate the behavior of net-proton in statistical Binomial distribution (BD) at = 200 GeV in Au + Au collisions. With the BD parameters extracted from RHIC/STAR, it is found that can be negative. Furthermore, the obtained becomes smaller when applying the same magnitude of experimental statistics and calculation method to simulations. In 0-10% centrality, there is a significant difference between the simulated result and theoretical expectation. Based on the extracted parameters and experimentally collected statistics, the baseline of net-proton in BD is presented.

Defect-Induced Phase Transition in Hafnium Oxide Thin Films: Comparing Heavy Ion Irradiation and Oxygen-Engineering Effects

Hafnium oxide acts as a functional dielectric in a variety of traditional and emerging nonvolatile memory technologies. To investigate the effect of heavy ion irradiation on its crystalline structure, highly textured hafnium oxide films were irradiated with 1.635 GeV Au ions of fluences ranging from 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> to 7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . For monoclinic hafnium oxide films, a fluence-dependent defect-induced phase transition to a defect-stabilized tetragonal phase is identified. In low-temperature tetragonal hafnium oxide films, the X-ray diffraction (XRD) patterns show an out-of-plane lattice constant decrease with increasing irradiation fluence. Observed crystalline changes are strikingly similar to trends found for oxygen-engineered hafnium oxide films, directly grown at varying oxidation conditions. The correlation of structural changes with in vacuo electron spectroscopy data of oxygen-engineered films suggests that the irradiation of hafnium oxide leads to an oxygen loss that increases with fluence. Therefore, the underlying mechanism of the monoclinic to tetragonal phase transition is obviously directly related to oxygen defects. This new information allows predictions of device stability under swift heavy ion irradiation of hafnium oxide-based devices.

Ion irradiation induced strain and structural changes in LiTaO3 perovskite* *This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the

LiTaO3 crystals irradiated with 3 MeV and 1.162 GeV Au ions were studied by single crystal x-ray diffraction and Raman scattering measurements. The maximum lattice strains after 3 MeV Au ion irradiation to a fluence of 1.2 × 1013 cm−2 were 1.2% and 0.6% along the c- and a-/b-axes, respectively. Two effects were observed in 1.162 GeV Au ion irradiated samples: (i) the (0006) and (1120) Bragg peaks were split into doublets, which suggested a subtle structural change due to slight modification of chemical composition; and (ii) the pre-damaged 1.2% lattice strain along the c-axis was relaxed to 0.9% after subsequent irradiation with 1.162 GeV Au ions, while relaxation along the a- or b-axis was not obvious. A distinct change in the Raman spectrum of the 〈0001〉 oriented LiTaO3 crystals was observed after 1.162 GeV Au ion irradiation, but no obvious change was observed in the 〈1120〉 oriented samples or in 3 MeV Au ion irradiated samples. Strain and structural changes in crystalline LiTaO3, with or without pre-existing defects, upon ion irradiation are delineated in its responding to inelastic ionization and elastic nuclear collisions.

A study of varLambda and bar{varLambda } polarization splitting by meson field in PICR hydrodynamic model

With the PICR hydrodynamic model, we study the polarization splitting between varLambda and bar{varLambda } at RHIC BES energy range, based on the meson field mechanism. Our results fit to the experimental data fairly well. Besides, two unexpected effect emerges: (1) the baryon density gradient has non-trivial and negative contribution to the polarization splitting; (2) for 7.7 GeV Au+Au collisions within the centrality range of 20–50%, the polarization splitting surprisingly increases with the centrality decreases. The second effect might help to explain the significant signal of polarization splitting measured in STAR’s Au+Au 7.7 Gev collisions.

Radiation damage and thermal annealing in tunnel structured hollandite materials

Three tunnel structured hollandite samples (Cs1.33Ga1.33Ti6.67O16, Cs1.33Fe1.33Ti6.67O16, and Cs1.33Zn0.67Ti7.33O16) with demonstrated thermodynamic stability and chemical durability were synthesized and irradiated by a 1.1 GeV Au ion beam in order to study effects of B-site dopants on radiation stability. A crystalline-to-amorphous transformation induced by the high-energy ion irradiation was confirmed by complementary characterization techniques sensitive to different length-scales, such as powder X-ray diffraction, Raman spectroscopy and neutron total scattering. High-temperature oxide melt solution calorimetry was performed to determine the energy landscape before and after ion irradiation. Together, structural and thermodynamic analyses demonstrated distinctly different radiation responses of the hollandite with different B-site dopants; the Ga-substituted hollandite exhibited the smallest enthalpy of damage indicating the best radiation stability among the three samples. The hypothesized origin of the different radiation responses is the structural feature in the binary oxide form of the respective B-site dopants (e.g., Ga2O3versus Fe2O3/ZnO for Ga and Fe/Zn dopants, respectively). Moreover, thermal analysis (i.e., differential scanning calorimetry) was conducted to investigate structural changes from the irradiation induced damaged states after thermal annealing. Results of thermal analysis revealed that the annealing-induced structural evolution of the radiation damaged hollandite structure is complex and decoupled at different length-scales. The long-range periodic structure (nanometers) was not recovered after thermal annealing and structural changes over a shorter range (≤ ∼3 Å) occurred in multiple steps during the annealing process.

Nuclear modification factors, directed and elliptic flow of electrons from open heavy flavor decays in Au+Au collisions from STAR

We present the analyses of single electrons from semileptonic bottom and charm hadron decays at mid-rapidity in sNN=200and54.4GeV Au+Au collisions (talk in Heavy-Flavor session III). The data at sNN=200GeV incorporate information from the Heavy Flavor Tracker which enables the topological separation of electrons originating from bottom and charm hadron decays. We report the first STAR measurements at sNN=200GeV of ν2 for bottom decay electrons as a function of pT and ν1 for charm decay electrons as a function of electron rapidity. Additionally, we present the improved measurements of heavy-flavor decay electron RAA and a new measurement of the ratio of RCP between bottom and charm decay electrons. Finally, we also report the measurement of non-photonic electron ν2 in sNN=54.4GeV data collected during the 2017 RHIC run.

Local Spin Polarization in 200 GeV Au+Au and 2.76 TeV Pb+Pb Collisions

We calculated the azimuthal angle dependence of the local spin polarization of hyperons in 200 GeV Au+Au and 2.76 TeV Pb+Pb collisions in the framework of the (3+1)D viscous hydrodynamic model CLVisc with AMPT initial conditions encoding initial orbital angular momenta. We find that the azimuthal angle dependence of the hyperon polarization strongly depends on the choice of the spin chemical potential Ωμν. With Ωμν chosen to be proportional to the temperature vorticity, our simulation shows coincidental results with the recent measurements at RHIC.