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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 OSTI2015

Hadron production in e + e - annihilation at BABAR, and implication for the muon anomalous magnetic moment

The BABAR collaboration has an extensive program of studying hadronic cross sections in low-energy e + e - collisions, accessible via initial-state radiation. Our measurements allow significant improvements in the precision of the predicted value of the muon anomalous magnetic moment. These improvements are necessary for illuminating the current 3.6 sigma difference between the predicted and the experimental values. We have published results on a number of processes with two to six hadrons in the final state. We report here the results of recent studies with final states that constitute the main contribution to the hadronic cross section in the energy region between 1 and 3 GeV, as e + e - → K + K - , π + π - , and e + e - → 4 hadrons

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Macroscopic kinematics of the Hall electric field under influence of carrier magnetic moments

The relativistic effect on electromagnetic forces yields two types of forces which depend on the velocity of the relevant particles: (i) the usual Lorentz force exerted on a moving charged particle and (ii) the apparent Lorentz force exerted on a moving magnetic moment. In sharp contrast with type (i), the type (ii) force originates due to the transverse field induced by the Hall effect (HE). This study incorporates both forces into a Drude-type equation with a fully spin-polarized condition to investigate the effects of self-consistency of the source and the resultant fields on the HE. We also examine the self-consistency of the carrier kinematics and electromagnetic dynamics by simultaneously considering the Drude type equation and Maxwell equations at low frequencies. Thus, our approach can predict both the dc and ac characteristics of the HE, demonstrating that the dc current condition solely yields the ordinary HE, while the ac current condition yields generation of both fundamental and second harmonic modes of the HE field. When the magnetostatic field is absent, the simultaneous presence of dc and ac longitudinal currents generates the ac HE that has both fundamental frequency and second harmonic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Magnetic moments and spin structure in single-phase B20 Co 1+x Si 1-x (x = 0.043)

Neutron powder diffraction (NPD) and x-ray magnetic circular dichroism (XMCD) spectroscopy are employed to investigate the magnetism and spin structure in single-phase B20 Co 1.043 Si 0.957 . The magnetic contributions to the NPD data measured in zero fields are consistent with the helical order among the allowed spin structures derived from group theory. The magnitude of the magnetic moment is (0.3 ± 0.1) μ B /Co according to NPD, while the surface magnetization probed by XMCD at 3 kOe is (0.18–0.31) μ B /Co. Both values are substantially larger than the bulk magnetization of 0.11 μ B /Co determined from magnetometry at 70 kOe and 2 K. Finally, these experimental data indicate the formation of a helical spin phase and the associated conical states in high magnetic fields.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Using infinite-volume, continuum QED and lattice QCD for the hadronic light-by-light contribution to the muon anomalous magnetic moment

In our previous work, the connected and leading disconnected hadronic light-by-light contributions to the muon anomalous magnetic moment (g — 2) have been computed using lattice QCD ensembles corresponding to physical pion mass generated by the RBC/UKQCD Collaboration. However, the calculation is expected to suffer from a significant finite-volume error that scales like 1/L 2 where L is the spatial size of the lattice. In this paper, we demonstrate that this problem is cured by treating the muon and photons in infinite-volume, continuum QED, resulting in a weighting function that is precomputed and saved with affordable cost and sufficient accuracy. We present numerical results for the case when the quark loop is replaced by a muon loop, finding the expected exponential approach to the infinite volume limit and consistency with the known analytic result. Here, we have implemented an improved weighting function which reduces both discretization and finite-volume effects arising from the hadronic part of the amplitude.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Reduction of the ordered magnetic moment and its relationship to Kondo coherence in Ce 1-x La x Cu 2 Ge 2

The microscopic details of the suppression of antiferromagnetic order in the Kondo-lattice series Ce 1-x La x Cu 2 Ge 2 due to nonmagnetic dilution by La are revealed through neutron diffraction results for x = 0:20, 0:40, 0:75, and 0:85. Magnetic Bragg peaks are found for 0:20 ≤ x ≤ 0:75, and both the Neel temperature, T N , and the ordered magnetic moment per Ce μ linearly decrease with increasing x. The reduction in μ points to strong hybridization of the increasingly diluted Ce 4f electrons, and we find a remarkable quadratic dependence of μ on the Kondo-coherence temperature. Here, we discuss our results in terms of local-moment- versus itinerant-type magnetism and mean-field theory, and show that Ce 1-x La x Cu 2 Ge 2 provides an exceptional opportunity to quantitatively study the multiple magnetic interactions in a Kondo lattice.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr 2 IrO 4

Here, we report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the ${{J}_{\text{eff}}}=1/2$ states in Sr 2 IrO 4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump–hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps–1.5 ns.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Lattice calculation of hadronic light-by-light contribution to the muon anomalous magnetic moment

The quark-connected part of the hadronic light-by-light scattering contribution to the muon’s anomalous magnetic moment is computed using lattice QCD with chiral fermions. Here we report several significant algorithmic improvements and demonstrate their effectiveness through specific calculations which show a reduction in statistical errors by more than an order of magnitude. The most realistic of these calculations is performed with a near-physical 171 MeV pion mass on a (4.6 fm) 3 spatial volume using the 32 3 ×64 Iwasaki+DSDR gauge ensemble of the RBC/UKQCD Collaboration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment from lattice QCD

The form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in lattice QCD+QED and QED. A non-perturbative treatment of QED is used and is checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed. Statistically significant signals are obtained. Initial results appear promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Beam dynamics corrections to measurements of the muon anomalous magnetic moment

The Muon $g-2$ experiment at Fermilab is making progress towards its physics goal of measuring the muon anomalous magnetic moment with the unprecedented precision of 140 parts per billion. In April 2021, the collaboration published the first measurement based on the first year of data taking. The second result is based on the second and third years of data taking combined. We discuss the corrections to the anomalous spin precession signal due to beam dynamics effects being used to determine the anomalous spin precession frequency for the second result.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A half-metallic half-Heusler alloy having the largest atomic-like magnetic moment at optimized lattice constant

For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a group IV element or a pnicitide. The atomic arrangements within a unit-cell show three configurations. Before this study, most of the predictions of half-metallic properties of half-Heusler alloys at the lattice constants differing from their optimized lattice constant. Based on the electropositivity of X and electronegativity of Z for half-Heusler alloys, we found that one of the configurations of LiCrS exhibits half-metallic properties at its optimized lattice constant of 5.803Å, and has the maximum atomic-like magnetic moment of 5μ B . In conclusion, the challenges of its growth and the effects of the spin-orbit effect in this alloy will be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Origin of the net magnetic moment in LaCoO 3

We use polarized neutron scattering to characterize the Bragg scattering intensity below T C =89.5 K at the (1,0,0) pseudocubic nuclear Bragg point of LaCoO 3 . Upon cooling in a field (FC), a net magnetic moment is apparent in Bragg scattering intensity, just as it was in previous magnetization measurements. Critical behavior associated with the net moment near T C upon cooling in small applied fields rapidly rounds with increasing field strength. We show, using a mean-field calculation, that this net moment can develop in a metastable state that forms upon FC, even when all the interactions in the system are antiferromagnetic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Four-flavour leading-order hadronic contribution to the muon anomalous magnetic moment

We present a four-flavour lattice calculation of the leading-order hadronic vacuum polarisation contribution to the anomalous magnetic moment of the muon, aμ hvp , arising from quark-connected Feynman graphs. It is based on ensembles featuring N f =2+1+1 dynamical twisted mass fermions generated by the European Twisted Mass Collaboration (ETMC). Several light quark masses are used in order to yield a controlled extrapolation to the physical pion mass. We employ three lattice spacings to examine lattice artefacts and several different volumes to check for finite-size effects. Including the complete first two generations of quarks allows for a direct comparison with phenomenological determinations of a μ hvp . The final result involving an estimate of the systematic uncertainty a μ hvp =6.74 (21)(18) 10 -8 shows a good overall agreement with these computations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

The anomalous magnetic moment of the muon in the Standard Model

We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α 5 ) with negligible numerical uncertainty. The electroweak contribution is suppressed by (m μ / M W ) 2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α 2 ) and is due to hadronic vacuum polarization, whereas at O(α 3 ) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first- principle, lattice-QCD approach. The final result reads $a$$^{SM}_{μ}$ = 116 591 810(43) × 10 −11 and is smaller than the Brookhaven measurement by 3.7σ. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. Furthermore, this and the prospects to further reduce the theoretical uncertainty in the near future – which are also discussed here – make this quantity one of the most promising places to look for evidence of new physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Run 2/3 measurement of the muon anomalous magnetic moment by the Muon g-2 experiment at Fermilab

The Muon g-2 experiment at Fermilab seeks to measure the muon magnetic moment anomaly, $a_μ=(g-2)/2$, with a final target precision of 0.14 parts-per-million (ppm). The experiment's initial result, published in 2021 using Run 1 data from 2018, confirmed the previous measurement at Brookhaven National Laboratory with a comparable sensitivity of 0.46 ppm. In 2023, a new result based on Run 2 and Run 3 data, collected in 2019 and 2020, was released. These datasets contain four times the data from Run 1, significantly enhancing sensitivity and achieving an unprecedented uncertainty of 0.20 ppm. This advancement resulted in a two-fold improvement in both statistical and systematic uncertainties. Here, we will discuss the muon $g-2$ measurement, the increased precision relative to the Run 1 result, and provide an outlook on future measurements which will incorporate datasets from 2021 to 2023. Additionally, we will explore the implications of comparing the new measurements with the latest Standard Model predictions for muon g-2.

Zaid, Estifa'a [Liverpool U.]↗
DOE OSTI2014

Baryon magnetic moments in large-N{sub c} chiral perturbation theory: Effects of the decuplet-octet mass difference and flavor symmetry breaking

The magnetic and transition magnetic moments of the ground-state baryons are computed in heavy baryon chiral perturbation theory in the large-N{sub c} limit, where N{sub c} is the number of colors. SU(3) symmetry breaking is systematically studied twofold: On the one hand, one-loop nonanalytic corrections of orders m{sub q}{sup 1/2} and m{sub q} ln m{sub q} are included, with contributions of baryon intermediate states from both flavor octet and flavor decuplet multiplets, assuming degeneracy between baryon states within a given flavor multiplet but nondegeneracy between baryons of different multiplets. On the other hand, perturbative SU(3) symmetry breaking is also analyzed by including all relevant leading-order operators that explicitly break SU(3) at linear order. The resultant expressions are compared with the available experimental data and with other determinations in the context of conventional heavy baryon chiral perturbation theory for three flavors of light quarks and at the physical value N{sub c}=3. The agreement reached is quite impressive.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Connected and leading disconnected hadronic light-by-light contribution to the muon anomalous magnetic moment with a physical pion mass

We report a lattice QCD calculation of the hadronic light-by-light contribution to the muon anomalous magnetic moment at a physical pion mass. The calculation includes the connected diagrams and the leading, quark-line-disconnected diagrams. We incorporate algorithmic improvements developed in our previous work. The calculation was performed on the 48 3 × 96 ensemble generated with a physical pion mass and a 5.5 fm spatial extent by the RBC and UKQCD Collaborations using the chiral, domain wall fermion formulation. We find a HLbL μ = 5.35(1.35) × 10 –10 , where the error is statistical only. The finite-volume and finite lattice-spacing errors could be quite large and are the subject of ongoing research. Finally, the omitted disconnected graphs, while expected to give a correction of order 10%, also need to be computed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Magnetic moment evolution and spin freezing in doped BaFe2As2

Fe-K β X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments μ bare in electron- and hole-doped BaFe 2 As 2 . At low temperature, μ bare is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances μ bare in the hole-doped region, which is naturally explained by the theoretically predicted crossover into a spin-frozen state. Our measurements demonstrate the importance of Hund’s-coupling and electronic correlations, especially for hole-doped BaFe 2 As 2 , as well as the inadequacy of a fully localized or fully itinerant description of the 122 family of Fe pnictides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗