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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Production of protons and light nuclei in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV with the STAR detector

We report the systematic measurement of protons and light nuclei production in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum (𝑝 𝑇 ) spectra of protons (𝑝) , deuterons (𝑑) , tritons (𝑡) , 3 He , and 4 He have been measured from midrapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields (𝑑⁢𝑁/𝑑⁢𝑦), average transverse momentum (⟨𝑝 𝑇 ⟩), yield ratios (𝑑/𝑝, 𝑡/𝑝, 3 He/𝑝, 4 He/𝑝), as well as the coalescence parameters (𝐵 2 ,𝐵 3 ). The 4⁢𝜋 yields for various particles are determined by utilizing the measured rapidity distributions, 𝑑⁢𝑁/𝑑⁢𝑦. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios (𝑁 𝑝 ×𝑁 𝑡 /𝑁$^{2}_{d}$) and compare them with various model calculations. Furthermore, the physics implications of these results on the production mechanism of light nuclei and the QCD phase structure are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Measurement of the production and elliptic flow of (anti)nuclei in Xe-Xe collisions at √sNN = 5.44 TeV

Measurements of (anti)deuteron and (anti) 3He production in the rapidity range |𝑦|<0.5 as a function of the transverse momentum and event multiplicity in Xe-Xe collisions at a center-of-mass energy per nucleon-nucleon pair of √𝑠𝑁⁢𝑁=5.44 TeV are presented. The coalescence parameters 𝐵2 and 𝐵3 are measured as a function of the transverse momentum per nucleon. The ratios between (anti)deuteron and (anti) 3He yields and those of (anti)protons and pions are reported as a function of the mean charged-particle multiplicity density and compared with two implementations of the statistical hadronization model and with coalescence predictions. The elliptic flow of (anti)deuterons is measured for the first time in Xe-Xe collisions and shows features similar to those already observed in Pb-Pb collisions, i.e., the mass ordering at low transverse momentum and the meson-baryon grouping at intermediate transverse momentum. The production of nuclei is particularly sensitive to the chemical freeze-out temperature of the system created in the collision, which is extracted from a grand-canonical-ensemble-based thermal fit, performed for the first time including light nuclei along with light-flavor hadrons in Xe-Xe collisions. The extracted chemical freeze-out temperature 𝑇chem=(154.2±1.1) MeV in Xe-Xe collisions is similar to that observed in Pb-Pb collisions and close to the crossover temperature predicted by lattice quantum chromodynamics calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Distribution function of nuclei from $\mathcal{e}^±$ scattering in the presence of a strong primordial magnetic field

The amplitude of the primordial magnetic field (PMF) is constrained from observational limits on primordial nuclear abundances. Within this constraint, it is possible that nuclear motion is regulated by Coulomb scattering with electrons and positrons (e ± s), while e ± s are affected by a PMF rather than collisions. For example, at a temperature of 10 9 K, thermal nuclei typically experience ~ 10 21 scatterings per second that are dominated by very small angle scattering leading to minuscule changes in the nuclear kinetic energy of order $\mathcal{O}$(1) eV. In this paper the upper limit on the effects of a possible discretization of the e ± momenta by the PMF on the nuclear momentum distribution is estimated under the extreme assumptions that the momentum of the e ± is relaxed before and after Coulomb scattering to Landau levels, and that during Coulomb scattering the PMF is neglected. This assumption explicitly breaks the time reversal invariance of Coulomb scattering, and the Maxwell-Boltzmann distribution is not a trivial steady state solution of the Boltzmann equation under these assumptions. Here we numerically evaluate the collision terms in the Boltzmann equation, and show that the introduction of a special direction in the e ± distribution by the PMF generates no directional dependence of the collisional destruction term of nuclei. Large anisotropies in the nuclear distribution function are then constrained from big bang nucleosynthesis. Ultimately, we conclude that a PMF does not significantly affect the isotropy or big bang nucleosynthesis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Cosmic ray spectrum of protons plus helium nuclei between 6 and 158 TeV from HAWC data

Here, a measurement with high statistics of the differential energy spectrum of light elements in cosmic rays, in particular, of primary H plus He nuclei, is reported. The spectrum is presented in the energy range from 6 to 158 TeV per nucleus. Data was collected with the High Altitude Water Cherenkov (HAWC) Observatory between June 2015 and June 2019. The analysis was based on a Bayesian unfolding procedure, which was applied on a subsample of vertical HAWC data that was enriched to 82% of events induced by light nuclei. To achieve the mass separation, a cut on the lateral age of air shower data was set guided by predictions of CORSIKA/QGSJET-II-04 simulations. The measured spectrum is consistent with a broken power-law spectrum and shows a kneelike feature at around E = 24.0$^{+3.6}_{-3.1}$ TeV , with a spectral index γ = -2.51 ± 0.02 before the break and with γ = -2.83 ± 0.02 above it. The feature has a statistical significance of 4.1σ. Within systematic uncertainties, the significance of the spectral break is 0.8σ.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Gravitational form factors of nuclei in the Skyrme model

Here, we compute the gravitational form factor D(t) of various nuclei in the generalized Skyrme model where nuclei are described as solitonic field configurations each with a definite baryon number B. We separately discuss the cases B = 1 (nucleons), B = 2 (deuteron), B = 3 (helium-3 and tritium), and extrapolate to larger B-values. Configurations with B > 1 are in general not spherically symmetric, and we demonstrate how group theory helps to extract the form factor. Numerical results are presented for the configurations with B = 1, 2, 3, 4, 5, 6, 7, 8, 32, 108. We find that the B-dependence is consistent with a power-law D(0) ∝ B β with β = 1.7–1.8. Other gravitational form factors can be calculated in the same framework, and we show the result for the J(t) form factor associated with the angular momentum for the B = 3 solution.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Accessing the gravitational form factors of the nucleon and nuclei through a massive graviton

In contrast to the electromagnetic form factors of the nucleon and nuclei that have been extensively studied in electron scattering, there is no known way to directly measure the gravitational form factors (GFFs), the off-forward hadronic matrix element of the QCD energy-momentum tensor. I suggest exploring the possibility to access the GFFs of the proton and nuclei in conjunction with massive graviton searches at future TeV-scale lepton-ion colliders. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering off Nuclei

Here, we present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the GIBUU model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Impact of Two-Body Currents on Magnetic Dipole Moments of Nuclei

We investigate the effects of two-body currents on magnetic dipole moments of medium-mass and heavy nuclei using the valence-space in-medium similarity renormalization group with chiral effective field theory interactions and currents. Focusing on near doubly magic nuclei from oxygen to bismuth, we have found that the leading two-body currents globally improve the agreement with experimental magnetic moments. Moreover, our results show the importance of multishell effects for Ca 41 , which suggest that the Z = N = 20 gap in Ca 40 is not as robust as in Ca 48 . The increasing contribution of two-body currents in heavier systems is explained by the operator structure of the center-of-mass dependent Sachs term. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Quantum Monte Carlo Calculations of Magnetic Form Factors in Light Nuclei

Here, we present Quantum Monte Carlo calculations of magnetic form factors in A = 6-10 nuclei, based on Norfolk two- and three-nucleon interactions, and associated one- and two-body electromagnetic currents. Agreement with the available experimental data for 6 Li, 7 Li, 9 Be and 10 B up to values of momentum transfer q ~ 3 fm -1 is achieved when two-nucleon currents are accounted for. We present a set of predictions for the magnetic form factors of 7 Be, 8 Li, 9 Li, and 9 C. In these systems, two body currents account for ~ 40-60% of the total magnetic strength. Measurements in any of these radioactive systems would provide valuable insights on the nuclear magnetic structure emerging from the underlying many-nucleon dynamics. A particularly interesting case is that of 7 Be, as it would enable investigations of the magnetic structure of mirror nuclei

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

First Measurement of Near-Threshold and Subthreshold 𝐽/𝜓 Photoproduction off Nuclei

We report on the first measurement of J/ψ photoproduction from nuclei in the photon energy range of 7 to 10.8 GeV, extending above and below the photoproduction threshold in the free proton of ∼ 8.2 GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive A(γ, e + e − p) reaction with a dilepton invariant mass M(e + e − ) ∼ m J/ψ = 3.1 GeV. The incoherent J/ψ photoproduction cross sections in the measured nuclei are extracted as a function of the incident photon energy, momentum transfer, and proton reconstructed missing light-cone momentum fraction. Comparisons with theoretical predictions assuming a dipole form factor allow extracting a gluonic radius for bound protons of p $\sqrt4⟨r^2⟩$ = 0.85 ± 0.14 fm. The data also suggest an excess of the measured cross section for sub-threshold production and for interactions with high missing light-cone momentum fraction protons. The measured enhancement can be explained by modified gluon structure for high-virtuality bound-protons.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Effect of competition of spherical and deformed shells in quasifission of superheavy nuclei

Quasifission and fusion-fission represent the two most likely reaction outcomes to occur postcapture in collisions leading to superheavy nuclei. As such, understanding these mechanisms and how they relate to one another is key to understanding the intricate dynamics that drive the formation (or dissociation) of the nascent compound nuclei formed in fusion reactions. This understanding directly translates to a more informed picture of suitable reaction partners and can provide vital information for experimental efforts to study the physics and chemistry of superheavy elements. In this work we report results from time-dependent simulations of 48 Ca + 238 U and 50 Ti + 236 Th reactions at incident energies just above the Coulomb barrier with a focus on the quasifission process that prevent the formation of a fully equilibrated 286 Cn compound nucleus. We study these reactions systematically and consider a wide range of initial configurations to extract a robust estimate of primary fragment yields for the quasifission process. Multiple preferred exit channels are observed, with both spherical and deformed shell effects in the heavy and light fragments driving contributions to the production yields depending on the initial configuration of the system. Orientation effects of the deformed actinide targets are found to be a primary driver of which exit channels are populated. Here, the impact of moving away from a doubly magic projectile is explored with implications towards the reactions considered for current and future superheavy searches.

Gumbel, Richard [Michigan State University, East L↗
DOE OSTI2025

Deuteron Evaporation from N = Z Compound Nuclei

Deuteron evaporation was observed from the N = Z compound nuclei 52 Fe ⋆ , 56 Ni ⋆ , and 64 Ge ⋆ in an experiment conducted at Argonne National Laboratory, USA. The experiment included a novel combination of two highly pixelated double-sided Si-strip detectors inside the Microball chargedparticle detection array, allowing for unequivocal discrimination of evaporated deuterons from protons and α particles. In conjunction with the Gammasphere array, Neutron Shell, and additional ancillary detectors, decay paths into various residual nuclei were investigated. The study provides insights into the competition of deuteron vs. proton-neutron evaporation as a function of available excitation energy and populated angular momentum. Results are interpreted using a statistical evaporation formalism for multiple subsequent particle emissions. The decisive factor in the comparison appears to be the available excitation energy in the residual system, with single nucleon evaporation preferred over deuteron evaporation for higher excitation energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Electromagnetic radii of light nuclei from variational Monte Carlo calculations

We present variational Monte Carlo calculations of charge and magnetic radii in 𝐴 ≤ 10 nuclei. The calculations are based on the Norfolk two- and three-nucleon interactions, and associated one- and two-nucleon electromagnetic charge and current operators derived up to next-to-next-to-next-to-leading order in the chiral expansion. The charge and magnetic radii are extracted from the respective form factors. We find that the charge radii are within 5% of the experimental values for the nuclei considered. For the magnetic radii, a comparison is available only with 3 H and 3 ⁢He electron scattering data that are affected by large error bars. We hope that our predictions foster an interest in precisely measuring magnetic radii of heavier systems.

lepton induced nuclear reactions↗
DOE OSTI2025

Probing Gluon Fluctuations in Nuclei with the First Energy-Dependent Measurement of Incoherent 𝐽/𝜓 Photoproduction in Ultraperipheral PbPb Collisions

Incoherent 𝐽/𝜓 photoproduction in heavy ion ultraperipheral collisions (UPCs) provides a sensitive probe of localized, fluctuating gluonic structures within heavy nuclei. This Letter reports the first measurement of the photon-nucleon center-of-mass energy (𝑊 𝛾⁢N ) dependence of this process in PbPb UPCs at a nucleon-nucleon center-of-mass energy of 5.02 TeV, using 1.52 nb −1 of data recorded by the CMS experiment. The measurement covers a wide 𝑊 𝛾⁢N range of ≈40–400 GeV, probing gluons carrying a fraction 𝑥 of nucleon momentum down to an unexplored regime of 6.5 ×10 −5 . Compared to baseline predictions neglecting nuclear effects, the measured cross sections exhibit significantly greater suppression at lower 𝑥. Additionally, the ratio of incoherent to coherent photoproduction is found to be constant across the probed 𝑊 𝛾⁢N and 𝑥 range, disfavoring the establishment of the black disk limit. This Letter provides critical insights into the 𝑥-dependent evolution of fluctuating gluonic structures within nuclei and calls for further advancements in theoretical models incorporating nuclear shadowing and gluon saturation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Calculated fission-fragment mass yields and average total kinetic energies of heavy and superheavy nuclei

Fission-fragment mass and total-kinetic-energy (TKE) distributions following fission of even-even nuclides in the region \(74 \le Z \le 126\) and \(92 \le N \le 230\) , comprising 896 nuclides have been calculated using the Brownian shape-motion method. The emphasis is the region of superheavy nuclei. To show compatibility with earlier results the calculations are extended to include earlier studied regions. An island of asymmetric fission is obtained in the superheavy region, \(106\le Z\le 114\) and \(162\le N\le 176\) , where the heavy fragment is found to be close to \(^{208}\) Pb and the light fragment adjusts accordingly. Most experimentally observed \(\alpha \) -decay chains of superheavy nuclei with \(Z > 113 \) terminate by spontaneous fission in our predicted region of asymmetric fission. In these cases, the pronounced large asymmetry is accompanied by a low TKE value compatible with measurements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Light-nuclei production and search for the QCD critical point

We discuss the potential of light-nuclei measurements in heavy-ion collisions at intermediate energies for the search of the hypothetical QCD critical end-point. A previous proposal based on neutron density fluctuations has brought appealing experimental evidences of a maximum in the ratio of the number of tritons times protons, divided over deuterons square, $\mathcal{O}_{tpd}$. However these results are difficult to reconcile with the state-of-the-art statistical thermal model predictions. Based on the idea that the QCD critical point can lead to a substantial attraction among nucleons, we propose new light-nuclei multiplicity ratios involving 4 He in which the maximum would be more noticeable. We argue that the experimental extraction is feasible by presenting these ratios formed from actual measurements of total and differential yields at low and high collision energies from FOPI and ALICE experiments, respectively. We also illustrate the possible behavior of these ratios at intermediate energies applying a semiclassical method based on flucton paths using the preliminary NA49 and STAR data for $\mathcal{O}_{tpd}$ as input.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Two photon exchange with nuclei from $e^+/e^-$ elastic cross section ratios

Hadronic box diagrams pose a significant source of radiative corrections to lepton scattering and β -decay measurements, yet their calculation remains highly model-dependent. Two-photon exchange is a box diagram generally relevant to most lepton scattering experiments, and is directly detectable via multiple observables. Single-spin asymmetries (SSA) are sensitive to the imaginary part of the TPE amplitude, while the ratio of $e^+/e^-$ elastic scattering cross sections is sensitive to the real part of the TPE amplitude. While SSA measurements have been reported for several complex nuclei, measurements of the $e^+/e^-$ ratio exist only for the proton. Proposed here is a measurement of the $e^+/e^-$ ratio on 4 He, a feasible nuclear target for which the ratio’s deviation from unity due to TPE is expected to be on order of 1–2%. Choosing a low Z nucleus minimizes Coulomb distortions, which could greatly overwhelm TPE for heavier nuclei. The proposed 19-day program, including measurements at three kinematic settings between 0.3 < Q 2 < 0.4 GeV 2 , would be made possible by the addition of a positron source at Jefferson Lab.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

A study of nuclear structure of light nuclei at the electron–ion collider

Understanding the substructure of atomic nuclei, particularly the clustering of nucleons inside them, is essential for comprehending nuclear dynamics. Various cluster configurations can emerge depending on excitation energy, the number and types of core clusters, and the presence of excess neutrons. Despite the prevalence of tightly bound cluster formations in low-lying states, understanding the correlation between clusters and their formation mechanisms remains incomplete. This exploring study investigates nuclear clustering at the electron–ion collider (EIC) using simulations based on the modified BeAGLE model. By simulating collisions involving e+ 9 Be, e+ 12 C, and e+ 16 O nuclei, we find that the average energy of particles and the system size ratios of particles at forward rapidity exhibit sensitivity to alpha clustering and its various configurations. These findings offer valuable insights into the dynamics of nuclear clustering and its implications for future studies at the EIC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗