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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
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electroweak nuclear radii constrain the isospin breaking correction to V ud

We lay out a novel formalism to connect the isospin-symmetry breaking correction to the rates of superallowed nuclear beta decays, δ C , to the isospin-breaking sensitive combinations of electroweak nuclear radii that can be accessed experimentally. We individuate transitions in the superallowed decay chart where a measurement of the neutron skin of a stable daughter even at a moderate precision could already help discriminating between models used to compute δ C . We review the existing experimental situation and make connection to the existing and future experimental programs.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Disoriented isospin condensates in heavy-ion collisions

Anomalous neutral to charged kaon correlations measured by the ALICE collaboration have defied usual explanations. We propose that the large fluctuations could arise because of a disoriented isospin condensate where there is an imbalance between up and down condensates at the time kaons hadronize. This could happen in heavy-ion collisions when the quark condensate re-forms as the system cools and the approximate chiral symmetry of QCD is broken. Within the linear sigma model, we show that the energy cost of forming a disoriented isospin condensate is small making it very plausible.

Kapusta, Joseph [University of Minnesota, Minneapo↗
DOE OSTI2025

High-isospin multiplets in 𝐴=15 and 16 nuclei

Isospin quartets (T=3/2) and quintets (T=2) have been investigated for A=15 and A=16 nuclei, respectively. Data from an invariant-mass experiment, with a 17 Ne beam, were reanalyzed and the T=3/2 and T=2 states in 15 O and 16 F, associated with p+ 14 N and 2p+ 14 N exit channels respectively, were found. In some cases, γ-ray gating was used to tag on events that decay to the excited 0 + , T=1 state in 14 N rather than the ground state. With the new states, the lowest-energy 1/2 + and 5/2 + quartets for A=15 and the 0 + and 2 + quintets for A=16 are completed. In addition, members of these multiplets in 15 F and 16 Ne decaying to the p+ 14 O and 2p+ 14 O channels are reevaluated by gating on events where the 14 O fragment recoils perpendicular to beam axis in the parent reference frame. Such transverse-decay events have the best invariant-mass resolution. No evidence for deviations from a quadratic dependence of the mass on the isospin projection was found for the A=15 quartets. However for the A=16 0 + and 2 + quintets, evidence for deviations were found.

Coulomb energies↗
DOE OSTI2023

Transformer spin-triplet superconductivity at the onset of isospin order in bilayer graphene

We consider the origin of superconductivity found recently in Bernal bilayer graphene at the onset of isospin-polarized order, trying to infer the pairing mechanism and superconducting order from the measurements available to date. The superconductivity is induced by a parallel magnetic field and persists well above the Pauli limit, indicating an unconventional scenario of quantum-critical pairing, where soft fluctuations of isospin give rise to spin-triplet superconductivity. We consider the scenario in which the pairing interaction is entirely repulsive, which stands in contrast to the typical quantum-critical pairing mechanisms. Superconductivity emerges through a “transformer” mechanism where, in the presence of an in-plane magnetic field, the incipient valley polarization converts a frequency-independent repulsion into one with a strong nonmonotonic frequency dependence. Such an interaction enables a nonzero solution for the pairing gap function that changes sign as a function of frequency. Furthermore, the same mechanism holds at zero field in the presence of spin-orbit coupling, providing a likely explanation for the recently observed superconductivity in bilayer graphene on the WSe 2 monolayer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Experimental identification of the T = 1 , J π = 6 + state of Co 54 and isospin symmetry in A = 54 studied via one-nucleon knockout reactions

In this paper, new experimental data obtained from γ-ray tagged one-neutron and one-proton knockout from 55 Co are presented. A candidate for the sought-after T = 1, T z = 0, J π = 6 + state in 54 Co is proposed based on a comparison to the new data on 54 Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full fp-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the A = 54, T = 1 triplet is studied by calculating the experimental c coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin J = 6 expected for the (1f 7/2 ) -2 two-hole configuration relative to the doubly magic nucleus 56 Ni. Lastly, the experimental quantities are compared to the theoretically predicted c coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (N 3 LO).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Isospin symmetry breaking in the mirror pair 73 Sr- 73 Br

The recent experimental observation of isospin symmetry breaking (ISB) in the ground states of the T=3/2 mirror pair 73 Sr- 73 Br is theoretically studied using large-scale shell-model calculations. The large valence space and the successful PFSDG-U effective interaction used for the nuclear part of the problem capture possible structural changes and provide a robust basis to treat the ISB effects of both electromagnetic and nonelectromagnetic origin. The calculated shifts and mirror-energy differences are consistent with the inversion of the I π =1/2 - ,5/2 - states between 73 Sr- 73 Br and suggest that the role played by the Coulomb interaction is dominant. Finally, an isospin breaking contribution of nuclear origin is estimated to be ≈25keV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Spectroscopic factors, overlaps, and isospin symmetry from an R -matrix point of view

Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: R -matrix theory is used as the primary tool to interoperate among the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships between the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon + 12 C, nucleon + 16 O, and nucleon + 26 Al are presented. A new approach to multilevel mirror symmetry is derived and applied to the first three 2 + states of 18 O and 18 Ne. Conclusions: In this work, the relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second 2 + state in 18 Ne deduced from the mirror state in 18 O is significantly larger than found in previous work. This finding has the effect of increasing the 17 F($\textit{p,γ}$) 18 Ne reaction rate in novae.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Proton decays in 16 Ne and 18 Mg and isospin-symmetry breaking in carbon isotopes and isotones

We report that proton-rich nuclei possess unique properties in the nuclear chart. Due to the presence of both continuum coupling and Coulomb interaction, phenomena such as halos, Thomas-Ehrman shift, and proton emissions can occur. Relevant experimental data are difficult to obtain, so that theoretical calculations are needed to understand nuclei at drip lines and to guide experimentalists. In particular, the 16 Ne and 18 Mg isotopes are supposed to be one-proton and/or two-proton emitting nuclei, but associated experimental data are either incomplete or even unavailable. Consequently, we performed Gamow shell model calculations of carbon isotones bearing A = 15 - 18 . Isospin-symmetry breaking occurring in carbon isotones and isotopes is also discussed. It is hereby shown that the mixed effects of continuum coupling and Coulomb interaction at drip lines generate complex patterns in isospin multiplets. Added to that, it is possible to determine the one-proton and two-proton widths of 16 Ne and 18 Mg . Obtained decay patterns are in agreement with those obtained in previous experimental and theoretical works. Moreover, to our knowledge, this is the first theoretical calculation of binding energy and partial decay widths of 18 Mg in a configuration interaction picture.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Role of isospin composition in low-energy nuclear fusion

We employ a microscopic approach that examines the impact of isospin dynamics on the process of low- energy nuclear fusion along an isotope chain and dependence on deformation. Our method utilizes the density constrained time-dependent Hartree-Fock theory (DC-TDHF), where isoscalar and isovector characteristics of the energy density functional (EDF) are examined in turn. This approach is applied to a series of fusion interactions of 176 Yb with increasingly neutron rich isotopes of calcium. By evaluating the contributions from the isoscalar and isovector components of the EDF, we look to quantify the influence of isospin composition on the conditions under which fusion is most likely to take place. Furthermore, our findings reveal that, in nonsymmetric systems, the isovector dynamics plays a significant role. Its typical effect is a reduction in the potential barrier, which turns into enhancement for neutron-rich systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Analog-antianalog isospin mixing in 47 K 𝛽−decay

Here, we have measured the isospin mixing of the 𝐼 𝜋 =1/2 + , 𝐸 𝑥 = 2.599 MeV state in nearly doubly magic 47 Ca with the isobaric analog 1/2 + state of 47 K . Using the TRIUMF atom trap for 𝛽 decay, we have measured a nonzero asymmetry of the progeny 47 Ca with respect to the initial 47 K spin polarization, which together with the 𝛽 asymmetry implies a nonzero ratio of Fermi to Gamow-Teller matrix elements 𝑦 = 0.098 ± 0.037 for the 1/2 + → 1/2 + transition. Interpreting 𝑦 as mixing between this state and the isobaric analog state implies a Coulomb matrix element magnitude 101 ± 37 keV. This relatively large matrix element supports a model from the literature of analog-antianalog isospin mixing, which predicts large matrix elements in cases involving excess neutrons over protons occupying more than one major shell. The result supports pursuing a search for time-reversal odd, parity-even, isovector interactions using a correlation in 47 K 𝛽 decay.

beta decay↗
DOE OSTI2025

Relaxation times for disoriented isospin condensates in high energy heavy ion collisions

Fluctuations between charged and neutral kaons measured by the ALICE Collaboration in Pb-Pb collisions at the CERN Large Hadron Collider (LHC) exceed conventional explanations. Previously it was shown that if the scalar condensate is accompanied by an electrically neutral isospin-1 field then the combination can produce large equilibrium fluctuations where ⟨$\overline{𝑢}$ ⁢𝑢⟩≠⟨ $\overline{𝑑}$𝑑⟩. Hadronizing strange and antistrange quarks might then strongly fluctuate between charged ($\overline{𝑢}$⁢𝑠 or $\overline{𝑠}$⁢𝑢) and neutral (𝑑⁢$\overline{𝑠}$⁢ or 𝑠⁢$\overline{𝑑}$) kaons. Here, we estimate the times for the condensates to achieve their equilibrium probability distributions within causal volumes in high energy heavy ion collisions. This is achieved by modeling the temperature dependence of the condensates, mesonic collective excitations, decay rates of the associated fields, and employing the Langevin and Fokker-Planck equations. Within this model, we find that the equilibration times are short compared with the expansion time, making disoriented isospin condensates a viable explanation for the anomalous fluctuations observed at the LHC.

Quark-gluon plasma↗
DOE OSTI2016

Isospin decomposition of γ N → N * transitions within a dynamical coupled-channels model

Here, by extending the dynamical coupled-channels analysis performed in our previous work to include the available data of photoproduction of pi mesons off neutrons, the transition amplitudes for the photoexcitation of the neutron-to-nucleon resonances, γn → N*, at the resonance pole positions are determined. The combined fits to the data for both the proton- and neutron-target reactions also revise our results for the resonance pole positions and the γp → N* transition amplitudes. Our results allow an isospin decomposition of the γN → N* transition amplitudes for the isospin I = 1/2 N* resonances, which is necessary for testing hadron structure models and gives crucial inputs for constructing models of neutrino-induced reactions in the nucleon resonance region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Measurements of B → D ¯ D s 0 * + ( 2317 ) decay rates and a search for isospin partners of the D s 0 * + ( 2317 )

In this work, we report improved measurements of the product branching fractions B ( B + → D ¯ 0 D s 0 * + ( 2317 ) ) × B ( D s 0 * + ( 2317 ) → D s + π 0 ) = ( 8. 0 - 1.2 + 1.3 ± 1.1 ± 0.4 ) × 1 0 - 4 and B ( B 0 → D - D s 0 * + ( 2317 ) ) × B ( D s 0 * + ( 2317 ) → D s + π 0 ) = ( 10. 2 - 1.2 + 1.3 ± 1.0 ± 0.4 ) × 1 0 - 4 , where the first errors are statistical, the second are systematic and the third are from D and D s + branching fractions. In addition, we report negative results from a search for hypothesized neutral ( z 0 ) and doubly charged ( z + + ) isospin partners of the D s 0 * + ( 2317 ) and provide upper limits on the product branching fractions B ( B 0 → D 0 z 0 ) × B ( z 0 → D s + π - ) and B ( B + → D - z + + ) × B ( z + + → D s + π + ) that are more than an order of magnitude smaller than theoretical expectations for the hypotheses that the D s 0 * + ( 2317 ) is a member of an isospin triplet. The analysis uses a 711 fb - 1 data sample containing 772 million B B ¯ -meson pairs collected at the Υ ( 4 S ) resonance in the Belle detector at the KEKB collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Evidence for Isospin Violation and Measurement of C P Asymmetries in B → K * ( 892 ) γ

Here, we report the first evidence for isospin violation in B → K*γ and the first measurement of the difference of CP asymmetries between B+→K*+γ and B 0 → K* 0 γ. This analysis is based on the data sample containing 772 × 10 6 $B\overline{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric e + e - collider. We find evidence for the isospin violation with a significance of 3.1σ, Δ 0+ = [+6.2 ± 1.5(stat) ± 0.6(syst) ± 1.2(f +- / f 00 )]% , where the third uncertainty is due to the uncertainty on the fraction of B + B - to B 0 B 0 production in Υ(4S) decays. The measured value is consistent with predictions of the standard model. The result for the difference of CP asymmetries is ΔA CP = [+2.4 ± 2.8(stat)± 0.5(syst)]% , consistent with zero. The measured branching fractions and CP asymmetries for charged and neutral B meson decays are the most precise to date. Finally, we also calculate the ratio of branching fractions of B 0 → K* 0 γ to B$0\atop{s}$ → Φγ.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Hidden Spin-Isospin Exchange Symmetry

The strong interactions among nucleons have an approximate spin-isospin exchange symmetry that arises from the properties of quantum chromodynamics in the limit of many colors, N c . However this large- N c symmetry is well hidden and reveals itself only when averaging over intrinsic spin orientations. Furthermore, the symmetry is obscured unless the momentum resolution scale is close to an optimal scale that we call Λ large-N c . We show that the large-N c derivation requires a momentum resolution scale of Λ large-N c ~ 500 MeV. We derive a set of spin-isospin exchange sum rules and discuss implications for the spectrum of 30 P and applications to nuclear forces, nuclear structure calculations, and three-nucleon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

QCD Constraints on Isospin-Dense Matter and the Nuclear Equation of State

Understanding the behavior of dense hadronic matter is a central goal in nuclear physics as it governs the nature and dynamics of astrophysical objects such as supernovae and neutron stars. Because of the nonperturbative nature of quantum chromodynamics (QCD), little is known rigorously about hadronic matter in these extreme conditions. Here, lattice QCD calculations are used to compute thermodynamic quantities and the equation of state of QCD over a wide range of isospin chemical potentials with controlled systematic uncertainties. Agreement is seen with chiral perturbation theory when the chemical potential is small. Comparison to perturbative QCD at large chemical potential allows for an estimate of the gap in the superconducting phase, and this quantity is seen to agree with perturbative determinations. Since the partition function for an isospin chemical potential μ I bounds the partition function for a baryon chemical potential μ B = 3 μ I / 2 , these calculations also provide rigorous nonperturbative QCD bounds on the symmetric nuclear matter equation of state over a wide range of baryon densities for the first time. Published by the American Physical Society 2025

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Equilibration dynamics and isospin effects in nuclear reactions

We discuss equilibration times and isospin effect for various quanti- ties in low-energy heavy-ion reactions. These include equilibration of mass, isospin, and total kinetic energy (TKE) in quasifission and deep-inelastic reactions. The calculations are performed using the time-dependent Hartree-Fock theory. The in- fluence of shell effects on the equilibration times are also discussed in the context of theoretical and experimental results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

The three-body cluster energy for the isospin asymmetric nucleonic matter in the LOCV formalism

Highlights: • The present LOCV symmetry energy becomes consistent with those of other approaches. • The TBI becomes important in the IASM computation, at the low proton to neutron ratio. • The TBC energy notably affects the IASM EOS around the saturation point. - Abstract: The equation of state (EOS) of the isospin asymmetric nucleonic matter (IASM) is studied in the Lowest Order Constrained Variational (LOCV) formalism, using the AV18 two-body potential with a density-dependent three-body interaction (TBI), which was proposed by Lagaris and Pandharipande (LP) in 1981. In the LOCV framework, an adjustment mechanism is introduced for finding the appropriate parameters of the TBI. It is shown that, assuming the TBI, the corresponding LOCV symmetric nuclear (pure neutron) matter results fairly agree with those of Fermi Hypernetted Chain (FHNC). Also, the contribution of the averaged three-body cluster (TBC) energy is evaluated, at different proton to neutron ratios R. Employing the TBI, up to ρ=0.5 fm{sup −3}, the TBC energy ranges from −6 to 6 MeV per particle which considerably changes the IASM EOS, especially at low densities. Moreover, employing the TBI, the LOCV IASM state-averaged correlation functions (effective potentials) and the nucleon–nucleon distribution functions (NNDF) are reported. It is illustrated that, by increasing the density (ratio R), the impact of the TBI becomes much more evident. Finally, it should be noted that, the IASM FHNC and Monte Carlo (MC) data are not available for comparison.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗