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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Moiré photonics and optoelectronics

Moiré superlattices, the artificial quantum materials, have provided a wide range of possibilities for the exploration of completely new physics and device architectures. In this Review, we focus on the recent progress on emerging moiré photonics and optoelectronics, including but not limited to moiré excitons, trions, and polaritons; resonantly hybridized excitons; reconstructed collective excitations; strong mid- and far-infrared photoresponses; terahertz single-photon detection; and symmetry-breaking optoelectronics. We also discuss the future opportunities and research directions in this field, such as developing advanced techniques to probe the emergent photonics and optoelectronics in an individual moiré supercell; exploring new ferroelectric, magnetic, and multiferroic moiré systems; and using external degrees of freedom to engineer moiré properties for exciting physics and potential technological innovations.

Science & Technology - Other Topics↗
DOE OSTI2022

Measurement of e + e – → $\mathrm{K^+K^–π^0}$ cross section and observation of a resonant structure

Based on collision data collected by the BESIII detector at the BEPCII collider at center-of-mass energies from 2.000 to 3.080 GeV, a partial-wave analysis is performed for the process $e^+e^–$→ $K^+K^–π^0$. The Born cross section of the process $e^+e^–$→ $K^+K^–π^0$ and its subprocesses $e^+e^–$ → $\phi π^0, K^{*+}$(892)$K^–$ and $K^{*+}_{2}$(1430)$K^–$ are measured. The results for $e^+e^–$→ $K^+K^–π^0$ and $\phi π^0$ are consistent with the BaBar measurements and with improved precision. By analyzing the cross sections of the subprocesses $e^+e^–$ → $K^{*+}$(892)$K^–$ and $K^{*+}_{2}$(1430)$K^–$ a structure with mass $M_R$ = (2190 ± 19 ± 37) MeV/c 2 and width $Γ_R$ = (191 ± 28 ± 60) MeV is observed with a combined statistical significance of 7.1σ. The measured resonance parameters suggest it can be identified as the $\phi$(2170), thus the results provide valuable input to understand the internal nature of this state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2010

Using Whispering-Gallery-Mode Resonators for Refractometry

A method of determining the refractive and absorptive properties of optically transparent materials involves a combination of theoretical and experimental analysis of electromagnetic responses of whispering-gallery-mode (WGM) resonator disks made of those materials. The method was conceived especially for use in studying transparent photorefractive materials, for which purpose this method affords unprecedented levels of sensitivity and accuracy. The method is expected to be particularly useful for measuring temporally varying refractive and absorptive properties of photorefractive materials at infrared wavelengths. Still more particularly, the method is expected to be useful for measuring drifts in these properties that are so slow that, heretofore, the properties were assumed to be constant. The basic idea of the method is to attempt to infer values of the photorefractive properties of a material by seeking to match (1) theoretical predictions of the spectral responses (or selected features thereof) of a WGM of known dimensions made of the material with (2) the actual spectral responses (or selected features thereof). Spectral features that are useful for this purpose include resonance frequencies, free spectral ranges (differences between resonance frequencies of adjacently numbered modes), and resonance quality factors (Q values). The method has been demonstrated in several experiments, one of which was performed on a WGM resonator made from a disk of LiNbO3 doped with 5 percent of MgO. The free spectral range of the resonator was approximately equal to 3.42 GHz at wavelengths in the vicinity of 780 nm, the smallest full width at half maximum of a mode was approximately equal to 50 MHz, and the thickness of the resonator in the area of mode localization was 30 microns. In the experiment, laser power of 9 mW was coupled into the resonator with an efficiency of 75 percent, and the laser was scanned over a frequency band 9 GHz wide at a nominal wavelength of approximately equal to 780 nm. Resonance frequencies were measured as functions of time during several hours of exposure to the laser light. The results of these measurements, plotted in the figure, show a pronounced collective frequency drift of the resonator modes. The size of the drift has been estimated to correspond to a change of 8.5 x 10(exp -5) in the effective ordinary index of refraction of the resonator material.

Matsko, Andrey↗
DOE OSTI2024

Enhanced light confinement in nonlocal resonant metasurfaces with weak multipolar scatterers

Stronger light confinement can be enabled by nanoantennas in the nanostructure and result in efficient control of the directionality of the scattering. We report on an observation of the well-pronounced multipolar resonances from nickel nanoantennas originating from collective effects. We show that the collective coupling of multipolar modes from weak scatterers can substantially enhance the electric dipole and quadrupole resonances. We also demonstrate the generalized lattice Kerker effect in this nanoantenna array. Resonant multipolar excitations within nickel nanoantenna arrays can significantly enhance phenomena such as magneto-optical effects, indicating promising potential for advanced applications in the field of nanophotonics and sensing.

Physics↗
DOE OSTI2023

Measurement of the B + /B 0 production ratio in e + e - collisions at the $\Upsilon$ (4S) resonance using B → J/Ψ($\ell\ell$)K decays at Belle

We measure the ratio of branching fractions for the $\Upsilon$ (4S) decays to B + B - and B 0 $\bar{B}$ 0 using B + → J/Ψ($\ell\ell$)K + and B 0 → J/Ψ($\ell\ell$)K 0 samples, where J/Ψ($\ell\ell$) stands for J/Ψ → $\ell$ + $\ell$ - ($\ell$ = e or μ), with 711 fb -1 of data collected at the $\Upsilon$ (4S) resonance with the Belle detector. We find the decay rate ratio of $\Upsilon$ (4S) → B + B - over $\Upsilon$ (4S) → B 0 $\bar{B}$ 0 to be 1.065 ± 0.012 ± 0.019 ± 0.047, which is the most precise measurement to date. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainty is due to the assumption of isospin symmetry in B → J/Ψ($\ell\ell$) K.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

The Effects of Long Duration Bed Rest as a Spaceflight Analogue on Resting State Sensorimotor Network Functional Connectivity and Neurocognitive Performance

Long duration spaceflight has been associated with detrimental alterations in human sensorimotor systems and neurocognitive performance. Prolonged exposure to a head-down tilt position during long duration bed rest can resemble several effects of the microgravity environment such as reduced sensory inputs, body unloading and increased cephalic fluid distribution. The question of whether microgravity affects other central nervous system functions such as brain functional connectivity and its relationship with neurocognitive performance is largely unknown, but of potential importance to the health and performance of astronauts both during and post-flight. The aims of the present study are 1) to identify changes in sensorimotor resting state functional connectivity that occur with extended bed rest exposure, and to characterize their recovery time course; 2) to evaluate how these neural changes correlate with neurocognitive performance. Resting-state functional magnetic resonance imaging (rsfMRI) data were collected from 17 male participants. The data were acquired through the NASA bed rest facility, located at the University of Texas Medical Branch (Galveston, TX). Participants remained in bed with their heads tilted down six degrees below their feet for 70 consecutive days. RsfMRI data were obtained at seven time points: 7 and 12 days before bed rest; 7, 50, and 65 days during bed rest; and 7 and 12 days after bed rest. Functional connectivity magnetic resonance imaging (fcMRI) analysis was performed to measure the connectivity of sensorimotor networks in the brain before, during, and post-bed rest. We found a decrease in left putamen connectivity with the pre- and post-central gyri from pre bed rest to the last day in bed rest. In addition, vestibular cortex connectivity with the posterior cingulate cortex decreased from pre to post bed rest. Furthermore, connectivity between cerebellar right superior posterior fissure and other cerebellar regions decreased from pre bed rest to the last day in bed rest. In contrast, connectivity within the default mode network remained stable over the course of bed rest. We also utilized a battery of behavioral measures including spatial working memory tasks and measures of functional mobility and balance. These behavioral measurements were collected before, during, and after bed rest. We will report the preliminary findings of correlations observed between brain functional connectivity and behavioral performance changes. Our results suggest that sensorimotor brain networks exhibit decoupling with extended periods of reduced usage. The findings from this study could aid in the understanding and future design of targeted countermeasures to alleviate the detrimental health and neurocognitive effects of long-duration spaceflight.

Cassady, K.↗
NASA NTRS2018

Tour Design Techniques for the Europa Clipper Mission

Europa is one of the most scientifically interesting targets of the solar system, as it may possess the three necessary ingredients for life: an extensive ocean of liquid water, an energy source from tidal heating, and a suite of biogenic elements. To explore the habitability of Europa, NASA is developing the Europa Clipper mission, currently scheduled to be launched in 2022. Europa resides deep inside the gravity well of Jupiter, in a region of the magnetosphere with many trapped ionized particles that get accelerated to near relativistic speeds; a Europa orbiter mission would require a large amount of ∆V for an orbit insertion maneuver, and would only return limited science data before being critically exposed to radiation. To mitigate these issues, Europa Clipper instead only utilizes Europa flybys, connected by Europa-resonant and non-resonant orbits. Science data is collected during high-radiation passes, and returned to Earth during the rest of the Jovian orbits, at a much lower radiation dose exposure. This paper will present several tour tools techniques developed for the design of the Europa Clipper flyby trajectory. In particular, the paper will describe different ways to perform fast line-of-apsides rotations; a new approach to improve the coverage of Europa’s trailing and leading edges, with the lighting conditions considerations; parametric studies of the expected radiation dose and time-of-flight as function of the Europa resonance; and a quick way to estimate the radiation dose for Jovian tours. Other techniques, that were already presented in previous papers, will be reviewed for completeness. We then implement some of the new approaches in the 18F17 tour.

Pellegrini, Etienne↗
DOE OSTI2024

Estradiol associations with brain functional connectivity in postmenopausal women

Abstract Objective Previous studies have found that estrogens play a role in functional connectivity in the brain; however, little research has been done regarding how estradiol is associated with functional connectivity in postmenopausal women. The purpose of this study was to examine the relationship between estradiol and functional connectivity in postmenopausal women. Methods Structural and blood oxygenation level–dependent resting-state magnetic resonance imaging scans of 88 cognitively healthy postmenopausal individuals were obtained along with blood samples collected the same day as the magnetic resonance imaging to assess hormone levels. We generated connectivity values in CONN toolbox version 20.b, an SPM-based software. Results A regression analysis was run using estradiol level and regions of interest (ROI), including the hippocampus, parahippocampus, dorsolateral prefrontal cortex, and precuneus. Estradiol level was found to enhance parahippocampal gyrus anterior division left functional connectivity during ROI-to-ROI regression analysis. Estradiol enhanced functional connectivity between the parahippocampal gyrus anterior division left and the precuneus as well as the parahippocampal gyrus anterior division left and parahippocampal gyrus posterior division right. An exploratory analysis showed that years since the final menstrual period was related to enhanced connectivity between regions within the frontoparietal network. Conclusions These results illustrated the relationship between estradiol level and functional connectivity in postmenopausal women. They have implications for understanding how the functioning of the brain changes for individuals after menopause that may eventually lead to changes in cognition and behavior in older ages.

Obstetrics & Gynecology↗
DOE OSTI2022

Optical Response of Periodic Arrays of Graphene Nanodisks

Doped graphene nanostructures are a promising platform for photonics due to their exceptionally strong and tunable plasmonic resonances. When placed in a periodic array configuration, the plasmons supported by the individual nanostructures interact with each other and, under the appropriate conditions, can give rise to a collective mode known as a lattice resonance. Here, for this study, we perform a comprehensive analysis of the response of periodic arrays of graphene nanodisks and identify the conditions under which the system is able to support lattice resonances. We find that the ratio between the period of the array and the wavelength of the plasmon completely determines the behavior of the system. As a consequence, strong lattice resonances are achieved for micron-size nanodisks in the terahertz regime. We develop a theoretical model valid beyond the electrostatic approximation and use it to derive closed analytical expressions for the strength, the wavelength, and the width of the optical resonance of the arrays. The theoretical framework developed in this work paves the way for facile design and discovery of emerging properties of periodic arrays of graphene nanostructures that could enable applications in photonics and plasmonics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Search for $ {\textrm{B}}_{\textrm{s}}^0 $ → ℓ ∓ τ ± with the semi-leptonic tagging method at Belle

We present a search for the lepton-flavor-violating decays ${B}_s^0$ → ℓ ∓ τ ± , where ℓ = e, μ, using the full data sample of 121 fb -1 collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. We use ${B}_s^0{\overline{B}}_s^0$ events in which one ${B}_s^0$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for (${B}_s^0$ → ℓ ∓ τ ± decays and set upper limits on their branching fractions at 90% confidence level as $\mathcal{B}$(${B}_s^0$ → e ∓ τ ± ) < 14 × 10 -4 and $\mathcal{B}$ (${B}_s^0$ → μ ∓ τ ± ) < 7.3 × 10 -4 . Our result represents the first upper limit on the ${B}_s^0$ → e ∓ τ ± decay rate.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Search for an axion-like particle in B → K (*) a(→ γγ) decays at Belle

We report a search for an axion-like particle a in B → K (*) a decays using data collected with the Belle detector at the KEKB asymmetric-energy electron-positron collider. The search is based on a 711 fb −1 data sample collected at the Υ(4S) resonance energy, corresponding to a sample of 772 × 10 6 Υ(4S) events. In this study, we search for the decay of the axion-like particle into a pair of photons, a → γγ. We scan the two-photon invariant mass in the range 0.16 GeV–4.50 GeV for the K modes and 0.16 GeV–4.20 GeV for the K * modes. No significant signal is observed in any of the modes, and 90% confidence level upper limits are established on the coupling to the W boson, g aW , as a function of a mass. The limits range from 3 × 10 −6 GeV −1 to 3 × 10 −5 GeV −1 , improving the current constraints on g aW by a factor of two over the most stringent previous experimental results.

B physics↗
DOE OSTI2025

Observation of the decays 𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$ and 𝐵 0 → Σ 𝑐 ⁢(2455) 0⁢ $\bar{Ξ}^0_𝑐$

We report the first observation of the two-body baryonic decays 𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$ and 𝐵 0 → Σ 𝑐 ⁢(2455) 0⁢ $\bar{Ξ}^0_𝑐$ with significances of 7.3⁢𝜎 and 6.2⁢𝜎, respectively, including statistical and systematic uncertainties. The branching fractions are measured to be ℬ⁡(𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$) = (5.74 ± 1.11 ± 0.4⁢2$^{+2.47}_{−1.53}$) ×10 −4 and ℬ⁡(𝐵 0 → Σ 𝑐 ⁢(2455) 0⁢ $\bar{Ξ}^0_𝑐$) = (4.83 ± 1.12 ± 0.3⁢7$^{+0.72}_{−0.60}$) ×10 −4 . The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the absolute branching fractions of $\bar{Ξ}^-_c$ or $\bar{Ξ}^0_𝑐$ decays. The data samples used for this analysis have integrated luminosities of 711 fb −1 and 365 fb −1 , and were collected at the ϒ⁡(4⁢𝑆) resonance by the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy 𝑒 + ⁢𝑒 − colliders, respectively.

branching fraction↗
DOE OSTI2023

Search for an s -wave resonance in Li 7 just above the proton-decay threshold

Near-threshold resonances play an important role in nucleosynthesis and applied nuclear science. The study of nuclei removed from stability has greatly extended the list of resonances close to decay thresholds. The no core shell model with continuum (NCSMC) recently predicted an s-wave resonance just above the proton-decay threshold of 7 Li at an excitation energy of 10.2 MeV. This potential case of a near-threshold resonance is dependent on the quantum mechanics of the p + 6 He fragments extended into the continuum. Further, the 6 He(d,n) 7 Li* reaction was employed in an attempt to populate this resonance and search for its proton decay via the invariant-mass method. No evidence of this resonance was found. However, the data collected in this search led to better constraints on the energy and width of the isobaric analog state (IAS) with (J π ,T) = (3/2 - , 3/2) and revealed a new weak resonance just above the IAS in energy, predicted by the NCSMC as a (J π , T ) = (3/2 – , 1/2) state and potentially a part of the antianalog structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Angular analysis of the low K + K – invariant mass enhancement in B + →K + K – π + decays

We study the decay B + →K + K – π + and investigate the angular distribution of K + K – pairs with invariant mass below 1.1 GeV / c 2 . This region exhibits both a strong enhancement in signal and very large direct CP violation. We construct a coherent sum model for the angular distribution of the S- and P-wave, and report the ratio of their amplitudes, the relative phase and the forward-backward asymmetry. We also report absolute differential branching fractions and direct CP asymmetry for the decay in bins of M K+K– and the differential branching fractions in bins of M K+π– . The results are based on a data sample that contains 772 × 10 6 $B\bar{B}$ pairs collected at the $Υ$(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. The result favors the presence of S- and D-waves in low M K+K– region to the detriment of a P-wave.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

First observation of B → $\bar{D}$ 1 (→ $\bar{D}$ π + π - ) $\ell$ + ν $\ell$ and measurement of the B → $\bar{D}$ (*) π$\ell$ + ν $\ell$ and B → $\bar{D}$ (*) π + π - $\ell$+ ν $\ell$ branching fractions with hadronic tagging at Belle

We report measurements of the ratios of branching fractions for B → $\bar{D}$(*) π$\ell$+ v $\ell$ and B → $\bar{D}$(*)π + π - $\ell$ + v $\ell$ relative to B → $\bar{D}$*$\ell$ + v $\ell$ decays with $\ell$ = e, μ. These results are obtained from a data sample that contains 772 × 10 6 $B\bar{B}$ pairs collected near the $\Upsilon$(4S) resonance with the Belle detector at the KEKB asymmetric energy e + e - collider.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Study of the lineshape of X ( 3872 ) using B decays to D 0 D ¯ * 0 K

We present a study of the X⁡(3872) lineshape in the decay B →X(3872)⁢K →D 0 $\overline{D}$ *0 ⁢K using a data sample of 772 ×10 6 B$\overline{B}$ pairs collected at the Y⁡(4⁢S) resonance with the Belle detector at the KEKB asymmetric-energy e +⁢ e - collider. The peak near the threshold in the D 0 $\overline{D}$ *0 invariant mass spectrum is fitted using a relativistic Breit-Wigner lineshape. We determine the mass and width parameters to be m BW =3873.7⁢1$^{+0.56}_{-0.50⁢}$(stat) ±0.13⁢(syst) MeV/c 2 and Γ BW =5.2$^{+2.2}_{-1.5}$⁢(stat) ±0.4⁢(syst) MeV, respectively. The branching fraction is found to be $\mathscr{B}$⁡(B + → X⁡(3872)⁢K + ) × $\mathscr{B}$⁡(X⁡(3872) → D 0 $\overline{D}$ *0 ) = (0.9⁢7$^{+0.21}_{-0.18}$⁢(stat) ± 0.10⁢(syst)) ×10 -4 . The signal from B 0 decays is observed for the first time with 5.2σ significance, and the ratio of branching fractions between charged and neutral B decays is measured to be $\mathscr{B}$(B 0 → X⁡(3872)⁢K 0 )/$\mathscr{B}$⁡(B + →X⁡(3872)⁢K + ) =1.34$^{+0.47}_{-0.40}$⁢(stat) $^{+0.10}_{-0.12}$⁢(syst). The peak is also studied using a Flatté lineshape. We determine the lower limit on the D 0 $\overline{D}$ * coupling constant g to be 0.075 at 95% credibility in the parameter region where the ratio of g to the mass difference from the D 0 $\overline{D}$ *0 threshold is equal to -15.11 GeV -1 , as measured by LHCb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for the decay B s 0 → π 0 π 0 at Belle

We report the results of the first search for the decay B$^{0}_{s}$ → π 0 ⁢π 0 using 121.4 fb -1 of data collected at the Y⁡(5⁢S) resonance with the Belle detector at the KEKB asymmetric-energy e + ⁢e - collider. We observe no signal and set a 90% confidence level upper limit of 7.7 ×10 -6 on the B$^{0}_{s}$ → π 0 π 0 decay branching fraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Evidence for B 0 → p Σ ¯ 0 π - at Belle

We search for the B 0 → p$\overline{Σ}$ 0 π - decay with $\overline{Σ}$ 0 → $\overline{Λ}$ γ, where the γ is not measured, using a data sample corresponding to an integrated luminosity of 711 fb -1 which contains 772 × 10 6 B$\overline{B}$ pairs, collected around the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. We measure for the first time the B 0 → p$\overline{Σ}$ 0 π - branching fraction to be $\mathscr{B}$(B 0 → p$\overline{Σ}$ 0 π - ) = $({1.17}_{-0.40}^{+0.43} (stat) ± 0.07(syst))$ X 10 -6 with a significance of 3.0σ. We simultaneously measure the branching fraction for the related channel B 0 → p$\overline{Λ}$ π - with much improved precision.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗