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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measurement of correlations among net-charge, net-proton, and net-kaon multiplicity distributions in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

Correlations among conserved quantum numbers, such as the net-electric charge, the net-baryon, and the net-strangeness in heavy-ion collisions, are crucial for exploring the QCD phase diagram. In this paper, these correlations are investigated using net-proton number (as a proxy for the net-baryon), net-kaon number (for the net-strangeness), and net-charged particle number in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with the ALICE detector. The observed correlations deviate from the Poissonian baseline, with a more pronounced deviation at LHC energies than at RHIC. Theoretical calculations of the Thermal-FIST hadron resonance gas model, HIJING, and EPOS LHC event generators are compared with experimental results, where a significant impact of resonance decays is observed. Thermal-FIST calculations under the grand canonical and canonical ensembles highlight significant differences, underscoring the role of local charge conservation in explaining the data. Recent lattice QCD studies have demonstrated that the magnetic field generated by spectator protons in heavy-ion collisions affects susceptibility ratios, in particular those related to the net-electric charge and the net-baryon numbers. The experimental findings are in qualitative agreement with the expectations of lattice QCD.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

First Measurement of 𝐴 = 4 Hypernuclei and Antihypernuclei at the LHC

In this Letter, the first evidence of the $^4_{\bar{Λ}}$$\overline{He}$ antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number 𝐴 = 4, specifically (anti)⁢$^4_Λ$H and (anti)⁢$^4_Λ$He. In addition, the antiparticle-to-particle ratios for both hypernuclei ($^4_{\bar{Λ}}$$\bar{H}$⁡/$^4_Λ$H and $^4_{\bar{Λ}}$$\overline{He}$/$^4_Λ$He) are shown, which are sensitive to the baryochemical potential of the strongly interacting matter created in heavy-ion collisions. The results are obtained from a data sample of central Pb-Pb collisions, collected during the 2018 LHC data taking at a center-of-mass energy per nucleon pair of $\sqrt{𝑠_{NN}}$ = 5.02 TeV. The yields measured for the average of the charge-conjugated states are found to be [0.78 ± 0.19⁢(stat) ± 0.17⁢(syst)] × 10 −6 for the (anti)⁢$^4_Λ$H and [1.08 ± 0.34⁢(stat)± 0.20⁢(syst)] × 10 −6 for the (anti)⁢$^4_Λ$He, and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of (anti)⁢$^4_Λ$H and (anti)⁢$^4_Λ$He excited states is expected to strongly enhance the production yield of these hypernuclei. The yield values exhibit a combined deviation of 3.3⁢𝜎 from the theoretical ground-state-only expectation, while the inclusion of the excited states in the calculations leads to an agreement within 0.6⁢𝜎 with the present measurements. Additionally, the measured (anti)$^4_Λ$H and (anti)⁢$^4_Λ$He masses are compatible with the world-average values within the uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

First measurement of D* + vector meson spin alignment in Pb–Pb collisions at $\sqrt{{s}_{\text{NN}}}={5}.0{2}$ TeV

The first measurement of prompt D *+ -meson spin alignment in ultrarelativistic heavy-ion collisions with respect to the direction orthogonal to the reaction plane is presented. The spin alignment is quantified by measuring the element ρ 00 of the diagonal spin-density matrix for prompt D *+ mesons with 4 < p T < 30 GeV/c in two rapidity intervals, |y| < 0.3 and 0.3 < |y| < 0.8, in central (0–10%) and midcentral (30–50%) Pb–Pb collisions at $\sqrt{{s}_{\text{NN}}}={5}.0{2}$ TeV. Evidence of spin alignment ρ 00 > 1/3 has been found for p T > 15 GeV/c and 0.3 < |y| < 0.8 with a significance of 3.1σ. The measured spin alignment of prompt D *+ mesons is compared with the one of inclusive J/ψ mesons measured at forward rapidity (2.5 < y < 4).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Study of $\langle {p}_{\text{T}}\rangle$ and its higher moments, and extraction of the speed of sound in Pb-Pb collisions with ALICE

Ultrarelativistic heavy-ion collisions produce a state of hot and dense strongly interacting QCD matter called quark-gluon plasma (QGP). On an event-by-event basis, the volume of the QGP in ultracentral collisions is mostly constant, while its total entropy can vary significantly due to quantum fluctuations, leading to variations in the temperature of the system. Exploiting this unique feature of ultracentral collisions allows for the interpretation of the correlation of the mean transverse momentum ($\langle$p T $\rangle$) of produced charged hadrons and the number of charged hadrons as a measure for the speed of sound, c s . This speed is related to the rate at which compression waves travel in the QGP and is determined by fitting the relative increase in $\langle$p T $\rangle$ with respect to the relative change in the average charged-particle density ($\langle$dN ch /dη$\rangle$) measured at mid-rapidity. This study reports the event-average $\langle$p T $\rangle$ of charged particles as well as the variance, skewness, and kurtosis of the event-by-event transverse momentum per charged particle ([p T ]) distribution in ultracentral Pb-Pb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair using the ALICE detector. Different centrality estimators based on charged-particle multiplicity or the transverse energy of the event are used to select ultracentral collisions. By ensuring a pseudorapidity gap between the region used to define the centrality and the region used to perform the measurement, the influence of biases and their potential effects on the rise of the mean transverse momentum is tested. The measured c$^{2}_{s}$ is found to strongly depend on the exploited centrality estimator and ranges between 0.1146±0.0028 (stat.)±0.0065 (syst.) and 0.4374±0.0006 (stat.)±0.0184 (syst.) in natural units. The self-normalized variance shows a steep decrease towards ultracentral collisions, while the self-normalized skewness variables show a maximum, followed by a fast decrease. These non-Gaussian features are understood in terms of the vanishing of the impact-parameter fluctuations contributing to the event-to-event [p T ] distribution.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Search for medium effects using jet axis decorrelation in inclusive jets from PbPb collisions at $\sqrt{{s}_{\text{NN}}}$ = 5.02 TeV

The jet axis decorrelation in inclusive jets is studied using lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The jet axis decorrelation is defined as the angular difference between two definitions of the jet axis. It is obtained by applying two recombination schemes on all the constituents of a given jet reconstructed by the anti-kT sequential algorithm with a distance parameter of R = 0.4. The data set, corresponding to an integrated luminosity of 0.66 nb −1 , was collected in 2018 with the CMS detector at the CERN LHC. The jet axis decorrelations are examined across collision centrality selections and intervals of jet transverse momentum. A centrality dependent evolution of the measured distributions is observed, with a progressive narrowing seen in more central events. This narrowing could result from medium-induced modification of the internal jet structure or reflect color charge effects in energy loss. This new measurement probes jet substructure in previously unexplored kinematic domains and show great promise for providing new insights on the color charge dependence of energy loss to jet-quenching models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

The high level trigger and express data production at STAR

To meet the demands of the Beam Energy Scan phase-II (BES-II) program, the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) developed a dual real-time framework consisting of a High Level Trigger (HLT) and an Express Data Production system (xProduction). The HLT operates online within the Data Acquisition (DAQ) chain on a dedicated multi-core CPU cluster with the option to offload compute-intensive kernels to Xeon Phi coprocessors. It uses parallelized algorithms, such as the Cellular Automaton (CA) Track Finder, to perform rapid tracking, vertexing, and event filtering. This allows it to select events of interest in real time and provide immediate feedback on detector and beam conditions. In contrast, the xProduction workflow runs concurrently and independently of the DAQ loop. It applies near offline-quality calibration and reconstruction within hours of data collection. The xProduction input is the express data stream, whose content can be enriched by HLT trigger/priority selections under DAQ/HLT resource constraints, and it uses the STAR calibration/conditions framework, incorporating online calibration/QA information when available. This enables early preliminary physics analysis, including the reconstruction of rare signals, such as hyperons and hypernuclei. It also provides collaboration-wide access to analysis-ready datasets. Together, the HLT and xProduction systems form a complementary architecture: the HLT performs online event selection while the xProduction chain delivers high-quality results within a short amount of time. This integrated framework has enabled the prompt reconstruction of the $^5_Λ$ He hypernucleus with high statistical significance and the efficient processing of hundreds of millions of heavy-ion collision events. In conclusion, its demonstrated scalability and robustness establish a model for future high-luminosity experiments requiring both online event filtering and rapid access to analysis-quality data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

CHICOX, a heavy-ion detection system for GRETA

The CHICOX detection system is an array of position sensitive parallel plate avalanche counters used for heavy ion detection in in-beam particle-gamma coincidence experiments. CHICOX, an upgrade of the CHICO2 array, is geometrically compatible with the GRETINA and GRETA gamma-ray arrays and provides an angular resolution sufficient to utilize the excellent position resolution of GRETINA/GRETA. CHICOX was successfully commissioned and fielded as an auxiliary detector to GRETINA in a campaign of stable-beam Coulomb excitation experiments at the ATLAS facility of Argonne National Laboratory. We report here on the design and in-beam performance of the CHICOX array.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Shell effects in quasi-fission: Reactions forming actinide and superheavy compound nuclei

Quasi-fission occurs in fully damped heavy-ion collisions following a significant mass transfer between the fragments, without formation of a compound nucleus. As in fission, quasi-fission is expected to be affected by quantum effects leading to asymmetric mass splits. Quantum shells stabilising fission fragments with octupole shapes have been invoked as a factor determining the distribution of nucleons between the fragments at scission, explaining the fact that the centroid of the heavy fragment charge distribution is found around Z = 54 protons in fission and quasi-fission of actinides. These shell effects are studied in microscopic studies of quasi-fission. In particular, time-dependent Hartree-Fock (TDHF) calculations have been performed for reactions forming actinides.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurement of substructure-dependent suppression of large-radius jets with charged particles in Pb+Pb collisions with ATLAS

Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions. This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of $R = 1.0$ and its dependence on the jet substructure. The measurement uses 1.72 nb$^{-1}$ of Pb+Pb data and 255 pb$^{-1}$ of $pp$ data, both at $\sqrt{s_{_\mathrm{NN}}} = 5.02$ TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering $R = 0.2$ calorimetric jets and are measured for transverse momentum above $200$ GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor ($R_\mathrm{AA}$). The jet $R_\mathrm{AA}$ is measured as a function of jet $p_{\mathrm{T}}$, the charged $k_t$ splitting scale ($\sqrt{d_{12}}$), and the angular separation ($dR_{12}$) of two leading sub-jets. The jet $R_\mathrm{AA}$ gradually decreases with increasing $\sqrt{d_{12}}$, implying significantly stronger suppression of large-radius jets with larger $k_t$ splitting scale. The jet $R_\mathrm{AA}$ gradually decreases for $dR_{12}$ in the range $0.01{-}0.2$ and then remains consistent with a constant for $ΔR_{12} \gtrsim 0.2$. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Nonperturbative heavy-flavor transport approach for hot QCD matter

The heavy charm and bottom quarks are unique probes of the transport properties of the quark-gluon plasma (QGP) and its hadronization in high-energy nuclear collisions. A key challenge in this context is to embed the interactions of the heavy quarks in the expanding medium compatible with the strong-coupling nature of the QGP, and thus to unravel the underlying microscopic mechanisms. In the present work we progress toward this goal by combining recent T -matrix interactions for elastic scattering with an effective transport implementation of gluon radiation, and apply these in a Langevin framework in a viscous hydrodynamic evolution. Hadronization of heavy quarks is evaluated using a modern recombination model with 4-momentum conservation, supplemented with fragmentation constrained by data in proton-proton collisions. Deploying this approach to charm-hadron observables in Pb-Pb collisions at the LHC yields fair agreement with experiment while also identifying areas of further systematic improvement of the simulations and its current input.

Heavy-flavor transport↗
DOE OSTI2025

Temperature measurement of Quark-Gluon plasma at different stages

In a Quark-Gluon Plasma (QGP), the fundamental building blocks of matter, quarks and gluons, are under extreme conditions of temperature and density. A QGP could exist in the early stages of the Universe, and in various objects and events in the cosmos. The thermodynamic and hydrodynamic properties of the QGP are described by Quantum Chromodynamics (QCD) and can be studied in heavy-ion collisions. Despite being a key thermodynamic parameter, the QGP temperature is still poorly known. Thermal lepton pairs (e + e − and μ + μ − ) are ideal penetrating probes of the true temperature of the emitting source, since their invariant-mass spectra suffer neither from strong final-state interactions nor from blue-shift effects due to rapid expansion. Here we measure the QGP temperature using thermal e+e− production at the Relativistic Heavy Ion Collider (RHIC). The average temperature from the low-mass region (in-medium ρ 0 vector-meson dominant) is (2.01 ± 0.23) × 10 12 K, consistent with the chemical freeze-out temperature from statistical models and the phase transition temperature from Lattice QCD. The average temperature from the intermediate mass region (above the ρ0 mass, QGP dominant) is significantly higher at (3.25 ± 0.60) × 10 12 K. This work provides essential experimental thermodynamic measurements to map out the QCD phase diagram and understand the properties of matter under extreme conditions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurement of inclusive jet cross section and substructure in 𝑝 + 𝑝 collisions at $\sqrt{s}$ = 200 GeV

The jet cross section and jet-substructure observables in 𝑝 + 𝑝 collisions at $\sqrt{s}$ =200 GeV were measured by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC). Jets are reconstructed from charged-particle tracks and electromagnetic-calorimeter clusters using the anti-𝑘 𝑡 algorithm with a jet radius of 𝑅 = 0.3 for jets with transverse momentum within 8.0 < 𝑝 𝑇 < 40.0 GeV/𝑐 and pseudorapidity |𝜂| < 0.15. Measurements include the jet cross section, as well as distributions of SoftDrop-groomed momentum fraction (𝑧 𝑔 ), charged-particle transverse momentum with respect to jet axis (𝑗 𝑇 ), and radial distributions of charged particles within jets (𝑟). Also measured was the distribution of 𝜉 = −ln⁡(𝑧), where 𝑧 is the fraction of the jet momentum carried by the charged particle. The measurements are compared to theoretical next-to and next-to-next-to-leading-order calculations, the PYTHIA and H erwig event generators, and to other existing experimental results. Indicated from these measurements is a lower particle multiplicity in jets at RHIC energies when compared to models. Also noted are implications for future jet measurements with sPHENIX at RHIC as well as at the future Electron-Ion Collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

First simultaneous measurement of the γ-ray and neutron emission probabilities in inverse kinematics at a heavy-ion storage ring

The probabilities for γ-ray and particle emission as a function of the excitation energy of a decaying nucleus are valuable observables for constraining the ingredients of the models that describe the deexcitation of nuclei near the particle emission threshold. These models are essential in nuclear astrophysics and applications. In this paper, we have for the first time simultaneously measured the γ-ray and neutron emission probabilities of 208 Pb. The measurement was performed in inverse kinematics at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, where a 208 Pb beam interacted through the 208 Pb (p,p') reaction with a hydrogen gas jet target. Instead of detecting the γ rays and neutrons emitted by 208 Pb, we detected the heavy beamlike residues produced after γ and neutron emission. These heavy residues were fully separated by a dipole magnet of the ESR and were detected with outstanding efficiencies. The comparison of the measured probabilities with model calculations has allowed us to test and select different descriptions of the γ-ray strength function and the nuclear level density available in the literature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Critical fluid dynamics in two and three dimensions

We describe a numerical method for simulating stochastic fluid dynamics near a critical point in the Ising universality class. This theory is known as model H, and is expected to govern the nonequilibrium dynamics of quantum chromodynamics (QCD) near a possible critical endpoint of the phase transition between a hadron liquid and the quark-gluon plasma. The numerical algorithm is based on a Metropolis scheme, and automatically ensures that the distribution function of the hydrodynamic variables in equilibrium is independent of the transport coefficients and only governed by the microscopic free energy. We verify dynamic scaling near the critical point of a two and three-dimensional fluid and extract the associated critical exponent z. Here, we find z≃3 in three dimensions, and z≃2 for a two-dimensional fluid. In a finite system, we observe a crossover between the mean field value z=4 and the true critical exponent z≃3 (z≃2 in d=2). This crossover is governed by the values of the correlation length and the renormalized shear viscosity.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurements at forward rapidity of elliptic flow of charged hadrons and open-heavy-flavor muons in Au + Au collisions at $\sqrt{𝑠_{𝑁⁢𝑁}}$ = 200 GeV

Here, we present the first forward-rapidity measurements of elliptic anisotropy of open-heavy-flavor muons at the Relativistic Heavy Ion Collider. The measurements are based on data samples of Au + Au collisions at $\sqrt{𝑠_{𝑁⁢𝑁}}$ = 200 GeV collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of 14.5 nb −1 . The measurements are performed in the pseudorapidity range 1.2 < |𝜂| < 2 and cover transverse momenta 1< 𝑝 𝑇 < 4 GeV/𝑐. The elliptic flow of charged hadrons as a function of transverse momentum is also measured in the same kinematic range. We observe significant elliptic flow for both charged hadrons and heavy-flavor muons. The results show clear mass ordering of elliptic flow of light- and heavy-flavor particles. The magnitude of the measured 𝑣 2 is comparable to that in the midrapidity region. This indicates that there is no strong longitudinal dependence in the quark-gluon-plasma evolution between midrapidity and the rapidity range of this measurement at $\sqrt{𝑠_{𝑁⁢𝑁}}$ = 200 GeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Soft-hard framework with exact four-momentum conservation for small systems

A new framework, called x-scape, for the combined study of both hard and soft transverse momentum sectors in high-energy proton-proton (𝑝−𝑝) and proton-nucleus (𝑝−𝐴) collisions is set up. A dynamical initial state is set up using the 3d-Glauber model with transverse locations of hotspots within each incoming nucleon. A hard scattering that emanates from two colliding hotspots is carried out using the Pythia generator. Initial state radiation from the incoming hard partons is carried out in a new module called I-matter, which includes the longitudinal location of initial splits. The energy-momentum of both the initial hard partons and their associated beam remnants is removed from the hot spots, depleting the energy-momentum available for the formation of the bulk medium. Outgoing showers are simulated using the matter generator, and results are presented for both cases, allowing for and not allowing for energy loss. First comparisons between this hard-soft model and single inclusive hadron and jet data from 𝑝−𝑝 and minimum bias 𝑝−Pb collisions are presented. Single hadron spectra in 𝑝−𝑝 are used to carry out a limited (in number of parameters) Bayesian calibration of the model. Fair comparisons with data are indicative of the utility of this new framework. Theoretical studies of the correlation between jet 𝑝 𝑇 and event activity at mid and forward rapidity are carried out.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Bottomonium properties in the quark-gluon plasma from a lattice-QCD informed 𝑇-matrix approach

Recent computations of bottomonium correlation functions with extended sources in lattice-discretized quantum chromodynamics (lQCD) provide new insights into heavy-quark dynamics at distance scales which are of the order of the inverse temperature. We analyze these results employing the thermodynamic 𝑇-matrix framework, in a continued effort to interpret lQCD data for quarkonium correlation functions in a nonperturbative and self-consistently solved quantum-many-body approach to a strongly coupled quark-gluon plasma (QGP). Its key inputs are the in-medium driving kernel (potential) of the scattering equation and an interference function which implements 3-body effects in the quarkonium coupling to the thermal medium. A simultaneous description of lQCD results for the bottomonium correlators with extended operators and the previously analyzed Wilson line correlators only requires minor refinements of the potential but calls for stronger interference effects at larger separation of the bottom quark and antiquark. We then analyze the poles of the self-consistent 𝑇 matrices on the real axis to assess the survival of the various bound states. Here, we estimate the pertinent temperatures where the poles disappear for the various bottomonium states and discuss the relation to the corresponding peaks in the bottomonium spectral functions. We also recalculate the spatial diffusion coefficient of the QGP and find it to be similar to that in our previous study.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Half-life determination of heavy ions in a storage ring considering feeding and depleting background processes

Heavy-ion storage rings have relatively large momentum acceptance which allows for multiple ion species to circulate at the same time. This needs to be considered in radioactive decay measurements of highly charged ions, where atomic charge exchange reactions can significantly alter the intensities of parent and daughter ions. In this study, we investigate this effect using the decay curves of ion numbers in the recent 205 Tl 81+ bound-state beta decay experiment conducted using the Experimental Storage Ring at GSI Darmstadt. To understand the intricate dynamics of ion numbers, we present a set of differential equations that account for various atomic and nuclear reaction processes—bound state beta decay, atomic electron recombination and capture, and electron ionization. By incorporating appropriate boundary conditions, we develop a set of differential equations that accurately simulate the decay curves of various simultaneously stored ions in the storage ring: 205 Tl 81+ , 205 Pb 81+ , 205 Pb 82+ , 200 Hg 79+ , and 200 Hg 80+ . Through a quantitative comparison between simulations and experimental data, we provide insights into the detailed reaction mechanisms governing stored heavy ions within the storage ring. Our approach effectively models charge-changing processes, reduces the complexity of the experimental setup, and provides a simpler method for measuring the decay half-lives of highly charged ions in storage rings.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗