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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 55 records · Page 3
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DOE OSTI2020

Ultracentral Collisions of Small and Deformed Systems at RHIC

We study a range of collision systems involving deformed ions and compare the elliptic and triangular flow harmonics produced in a hydrodynamics scenario versus a color glass condensate (CGC) scenario. For the hydrodynamics scenario, we generate initial conditions using TRENTO and work within a linear response approximation to obtain the final flow harmonics. For the CGC scenario, we use the explicit calculation of two-gluon correlations taken in the high-p T “(semi)dilute-(semi)dilute” regime to express the flow harmonics in terms of the density profile of the collision. Here, we consider ultracentral collisions of deformed ions as a testbed for these comparisons because the difference between tip-on-tip and side-on-side collisions modifies the multiplicity dependence in both scenarios, even at zero impact parameter. We find significant qualitative differences in the multiplicity dependence obtained in the initial conditions+hydrodynamics scenario and the CGC scenario, allowing these collisions of deformed ions to be used as a powerful discriminator between models. We also find that sub-nucleonic fluctuations have a systematic effect on the elliptic and triangular flow harmonics which are most discriminating in 0–1% ultracentral symmetric collisions of small deformed ions and in 0–10% d197Au collisions. The collision systems we consider are 238 U 238 U, d 197 Au, 9 Be 197 Au, 9 Be 9 Be, 3 He 3 He, and 3 He 197 Au.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Progress and challenges in small systems

Here, we present a comprehensive review of the theoretical and experimental progress in the investigation of novel high-temperature quantum chromodynamics phenomena in small systems at both the Relativistic Heavy Ion Collider and the Large Hadron Collider. We highlight the challenges and opportunities associated with studying small systems, by which we generally mean collision systems that involve at least one light ion or even a photon projectile. We discuss perspectives on possible future research directions to better understand the underlying physics at work in the collisions of small systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Progress and challenges in small systems

We present a comprehensive review of the theoretical and experimental progress in the investigation of novel high-temperature quantum chromodynamics phenomena in small systems at both the Relativistic Heavy Ion Collider and the Large Hadron Collider. We highlight the challenges and opportunities associated with studying small systems, by which we generally mean collision systems that involve at least one light ion or even a photon projectile. Here, we discuss perspectives on possible future research directions to better understand the underlying physics at work in the collisions of small systems.

collective behavior↗
DOE OSTI2022

Collectivity in Ultraperipheral Pb+Pb Collisions at the Large Hadron Collider

In this work, we present the first full (3+1)D dynamical simulations of ultraperipheral Pb+Pb collisions at the Large Hadron Collider. Extrapolating from p + Pb collisions, we explore whether a quasireal photon γ* interacting with the lead nucleus in an ultraperipheral collision can create a many-body system exhibiting fluid behavior. Assuming strong final-state interactions, we provide model results for charged hadron multiplicity, identified particle mean transverse momenta, and charged hadron anisotropic flow coefficients, and compare them with experimental data from the ALICE and ATLAS Collaborations. The elliptic flow hierarchy between p + Pb and γ*+Pb collisions is dominated by the difference in longitudinal flow decorrelations and reproduces the experimental data well. We have demonstrated that our theoretical framework provides a quantitative tool to study particle production and collectivity for all system sizes, ranging from central heavy-ion collisions to small asymmetric collision systems at the Relativistic Heavy-Ion Collider and the Large Hadron Collider and even at the future Electron-Ion Collider.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Observable signatures of initial state momentum anisotropies in nuclear collisions

In this work, we show that the correlation between the elliptic momentum anisotropy v 2 and the average transverse momentum [ p T ] at fixed multiplicity in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+ music +UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the color glass condensate predicts a characteristic sign change of the correlator ρ ^ ( v 2 2 , [ p T ] ) as a function of charged particle multiplicity in p + Au and d + Au collisions at s = 200 GeV , and p + Pb collisions at s = 5.02 TeV . This sign change is absent in calculations without initial state momentum anisotropies. The model further predicts a qualitative difference between the centrality dependence of ρ ^ ( v 2 2 , [ p T ] ) in Au + Au collisions at s = 200 GeV and Pb + Pb collisions at s = 5.02 TeV , with only the latter showing a sign change in peripheral events. Predictions for O + O collisions at different collision energy show a similar behavior. Experimental observation of these distinct qualitative features of ρ ^ ( v 2 2 , [ p T ] ) in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the color glass condensate effective theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

System-size scan of D meson R AA and v n using PbPb, XeXe, ArAr, and OO collisions at energies available at the CERN Large Hadron Collider

Here, experimental measurements indicate no suppression (e.g. R pPb ~ 1) but a surprisingly large D meson v 2 was measured in pPb collisions. In order to understand these results we use Trento+v-USPhydro+DAB-MOD to make predictions and propose a system size scan at the LHC involving 208 PbPb, 129 XeXe, 40 ArAr, and 16OO collisions. We find that the nuclear modification factor approaches unity as the system size is decreased, but nonetheless, in the 0–10% most central collisions v 2 {2} is roughly equivalent regardless of system size. These results arise from a rather non-trivial interplay between the shrinking path length and the enhancement of eccentricities in small systems at high multiplicity. Finally, we also find a surprising sensitivity of D mesons v 2 {2} in 0–10% at p T = 2–10 GeV to the slight deformation of 129 Xe recently found at LHC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

The smallest fluid on earth

High energy heavy ion collisions create quark gluon plasmas that behave like almost perfect fluids. Very similar features to those that led to this insight have also been observed in experimental data from collisions of small systems, involving protons or other light nuclei. Here we describe recent developments aimed at understanding whether, and if so how, systems that produce relatively few particles (orders of magnitude less than in typical heavy ion collisions) and are only one to a few times the size of a proton, can behave like fluids. This involves a deeper understanding of fluid dynamics and its applicability, improvements of our understanding of the initial geometry of the collisions by considering fluctuations of the proton shape, as well as advancements in the calculation of initial state effects within an effective theory of quantum chromodynamics, which can affect the observables that are used to study fluid behavior. We further address open questions and discuss future directions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Number of constituent quark scaling of elliptic flows in high multiplicity p-Pb collisions at $\sqrt{s_{NN}}$=5.02TeV

In this work, we briefly summarize our recent study on the number of constituent quark (NCQ) scaling of hadron elliptic flows in high multiplicity p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. With the inclusion of hadron production via the quark coalescence model at intermediate p T , the viscous hydrodynamics at low p T , and jet fragmentation at high p T , our Hydro – Coal – Frag model provides a nice description of the p T -spectra and differential elliptic flow v 2 (p T ) of pions, kaons and protons over the pT range from 0 to 6 GeV. Our results demonstrate that including the quark coalescence is essential for reproducing the observed approximate NCQ scaling of hadron v 2 at intermediate p T in experiments, indicating strongly the existence of partonic degrees of freedom and the formation of quark-gluon plasma in high multiplicity p-Pb collisions at the LHC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Collectivity in ultra-peripheral heavy-ion collisions

We present full (3+1 )D dynamical simulations to study collective behavior in ultra-peripheral nucleus-nucleus collisions (UPC) at the Large Hadron Collider (LHC) with the 3DGlauber+MUSIC+UrQMD framework [1, 2]. By extrapolating from asymmetric p+Pb collisions, we simulate a quasi-real photon γ* interacting with the Pb nucleus in an ultra-peripheral collision at the LHC, assuming strong final-state effects. We study the elliptic flow hierarchy between p+Pb and γ*+Pb collisions, which is dominated by the difference in longitudinal flow decorrelations. Our theoretical framework provides a quantitative tool to study collectivity in small asymmetric collision systems at current and future collider experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Exploring new small system geometries in heavy ion collisions [Slides]

We explore various new collision geometries in the context of the publicly available hydrodynamic model SONIC. We incorporate full A-nucleon configurations for 4 He, 12 C, and 16 O obtained from quantum Monte Carlo calculations with realistic nuclear potentials, and use a Monte Carlo Glauber calculation for the initial conditions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Measurement of the longitudinal flow-plane decorrelation using multiplane cumulants in $\sqrt{s_{NN}}$ = 200 GeV Au+Au, Ru+Ru, and Zr+Zr collisions

Measurements of the variation of anisotropic flow-plane angles (𝛹 𝑛 ) with rapidity, commonly known as the flow-plane decorrelation, provide important insights into the initial conditions of the matter produced in heavy-ion collisions. Here, in this paper, using data collected by the STAR experiment, we report the first measurement of the four-plane correlator observable 𝑇 𝑛 ⁡{𝑏⁢𝑎;𝑑⁢𝑐}=⟨⟨sin⁡[𝑛⁢(𝛹$^𝑏_𝑛$ − 𝛹$^𝑎_𝑛$)]⁢sin⁡[𝑛⁢(𝛹$^𝑑_𝑛$ − 𝛹$^𝑐_𝑛$)]⟩⟩, where superscripts 𝑎, 𝑏, 𝑐, and 𝑑 denote sequential pseudorapidity (𝜂) regions with 𝑎 corresponding to the most backward region, 𝑏 and 𝑐 close to mid-rapidity with 𝜂 𝑏 < 0 and 𝜂 𝑐 > 0, and 𝑑 being the most forward. The measurement is performed for the elliptic and triangular flow (i.e.~𝑛 = 2 and 3) in Au+Au and isobar (Ru+Ru, Zr+Zr) collisions at $\sqrt{s_{NN}}$=200~GeV. The goal of calculating the correlation of the flow-plane angle variations from backward to mid-central, and from mid-central to forward regions, is to probe the systematic variation of flow angle over a wide 𝜂 range. In mid-central collisions (10−30% centrality), we find 𝑇 2 ⁡{𝑏⁢𝑎;𝑑⁢𝑐} =−0.004 ±0.001⁢(s⁢t⁢a⁢t) ±0.002⁢(s⁢y⁢s⁢t) independent of the collision system. Such a small value of 𝑇 2 favors a random-walk'' variation of the flow-plane angles, where the rapidity correlation length is smaller than the entire region under study. These measurements provide new information on the decorrelation patterns in the system and offer a quantitative estimate of possible systematic variations in anisotropic flow angles such astwist’’ between forward and backward regions. This opens new opportunities for understanding the three-dimensional structure and the time evolution of the quark-gluon plasma created in heavy-ion collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Identified charged-hadron production in 𝑝+Al, 3 He + Au, and Cu + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and in U + U collisions at $\sqrt{s_{NN}}$ = 193 GeV

The PHENIX experiment has performed a systematic study of identified charged-hadron (𝜋 ± , 𝐾 ± , 𝑝, $\bar{𝑝}$) production at midrapidity in 𝑝 + Al, 3 He + Au, and Cu + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U + U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Identified charged-hadron invariant transverse-momentum (𝑝 𝑇 ) and transverse-mass (𝑚 𝑇 ) spectra are presented and interpreted in terms of radially expanding thermalized systems. The particle ratios of 𝐾/𝜋 and 𝑝/𝜋 have been measured in different centrality ranges of large (Cu + Au and U + U) and small (𝑝 + Al and 3 He + Au) collision systems. The values of 𝐾/𝜋 ratios measured in all considered collision systems were found to be consistent with those measured in 𝑝+𝑝 collisions. However, the values of 𝑝/𝜋 ratios measured in large collision systems reach the values of ≈0.6, which is a factor of ≈2 larger than in 𝑝 + 𝑝 collisions. These results can be qualitatively understood in terms of the baryon enhancement expected from hadronization by recombination. Identified charged-hadron nuclear-modification factors (𝑅 𝐴⁢𝐵 ) are also presented. Enhancement of proton 𝑅 𝐴⁢𝐵 values over meson 𝑅 𝐴⁢𝐵 values was observed in central 3 He + Au, Cu + Au, and U + U collisions. Finally, the proton 𝑅 𝐴⁢𝐵 values measured in the 𝑝 + Al collision system were found to be consistent with 𝑅 𝐴⁢𝐵 values of 𝜙, 𝜋 ± , 𝐾 ± , and 𝜋 0 mesons, which may indicate that the size of the system produced in 𝑝 + Al collisions is too small for recombination to cause a noticeable increase in proton production.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

3D multi-system Bayesian calibration with energy conservation to study rapidity-dependent dynamics of nuclear collisions

Considerable information about the early-stage dynamics of heavy ion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems — large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition, which we calibrate on the hadron multiplicity and anisotropic flow coefficients. We utilize Bayesian inference to constrain properties of the early- and late-time dynamics of the system, and highlight the impact of enforcing global energy conservation in our 3D model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

\(J/\psi \) and \(\psi (2S)\) Production in Small Systems with PHENIX

The suppression of the ψ(2S) nuclear modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, deviations of the nuclear modification from unity had been attributed to cold nuclear matter effects until the observation of strong differential suppression of the ψ(2S) state in p/d+A collisions, which suggests the presence of final-state effects. Here in this paper, we present results of J/ψ and ψ(2S) measurements in the dimuon decay channel for p + p, p+Al, and p+Au collision systems at $\sqrt{s_{NN}}$ = 200 GeV. Key results include the nuclear modification factors R pA as a function of centrality and rapidity. The measurements are compared with shadowing and transport model predictions, as well as complementary measurements at LHC energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Bulk properties and multi-particle correlations in large and small systems

Charged particle production is calculated in a hybrid framework consisting of the IP-Glasma initial state, Music viscous relativistic fluid dynamics, and the UrQMD microscopic hadronic cascade. Using one set of parameters, we compute observables for a large variety of collision systems. Furthermore, we compare to experimental data in p+p, p+Pb, Xe+Xe, Au+Au and Pb+Pb collisions at various energies, and make predictions for potential O+O runs at RHIC and LHC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of ψ ( 2 S ) nuclear modification at backward and forward rapidity in p + p , p + Al , and p + Au collisions at s N N = 200 GeV

Suppression of the J/ψ nuclear-modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, the nuclear modification was attributed to cold-nuclear-matter effects until the observation of strong differential suppression of the ψ(2S) state in p+A and d+A collisions suggested the presence of final-state effects. Results of J/ψ and ψ(2S) measurements in the dimuon decay channel are presented here for p+p, p+Al, and p+Au collision systems at $\sqrt{^{S}NN}$ = 200 GeV. The results are predominantly shown in the form of the nuclear-modification factor, R pA , the ratio of the ψ(2S) invariant yield per nucleon-nucleon collision in collisions of proton on target nucleus to that in p+p collisions. Finally, measurements of the J/ψ and ψ(2S) nuclear-modification factor are compared with shadowing and transport-model predictions, as well as to complementary measurements at Large-Hadron-Collider energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Enhanced production of strange baryons in high-energy nuclear collisions from a multiphase transport model

Here, we introduce additional coalescence factors for the production of strange baryons in a multiphase transport (AMPT) model in order to describe the enhanced production of multistrange hadrons observed in Pb + Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV at the Large Hadron Collider (LHC) and Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at Relativistic Heavy-Ion Collider (RHIC). This extended AMPT model is found to also give a reasonable description of the multiplicity dependence of the strangeness enhancement observed in high multiplicity events in $\textit{pp}$ collisions at $\sqrt{s}$ = 7 TeV and $\textit{p}$-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. We find that the coalescence factors depend on the system size but not much on whether the system is produced from A + A or $\textit{p}$ + A collisions. Here, the extended AMPT model thus provides a convenient way to model the mechanism underlying the observed strangeness enhancement in collisions of both small and large systems at RHIC and LHC energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Strong Constraints on Jet Quenching in Centrality-Dependent p + Pb Collisions at 5.02 TeV from ATLAS

Jet quenching is the process of color-charged partons losing energy via interactions with quark-gluon plasma droplets created in heavy-ion collisions. The collective expansion of such droplets is well described by viscous hydrodynamics. Similar evidence of collectivity is consistently observed in smaller collision systems, including p p and p + Pb collisions. In contrast, while jet quenching is observed in Pb + Pb collisions, no evidence has been found in these small systems to date, raising fundamental questions about the nature of the system created in these collisions. The ATLAS experiment at the Large Hadron Collider has measured the yield of charged hadrons correlated with reconstructed jets in 0.36 nb -1 of p + Pb and 3.6 pb -1 of pp collisions at 5.02 TeV. The yields of charged hadrons with ${p}^{ch}_{T}$ > 0.5 GeV near and opposite in azimuth to jets with ${p}^{jet}_{T}$ > 30 or 60 GeV, and the ratios of these yields between p + Pb and pp collisions, I pPb , are reported. The collision centrality of p + Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The I pPb values are consistent with unity within a few percent for hadrons with ${p}^{ch}_{T}$ > 4 GeV at all centralities. These data provide new, strong constraints that preclude almost any parton energy loss in central p + Pb collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗