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J. Kim

Publications and source records attributed to J. Kim.

At least 91 records · Page 5Linked to original sources
arXiv2023

A search for new physics in low-energy electron recoils from the first LZ exposure

The LUX-ZEPLIN (LZ) experiment is a dark matter detector centered on a dual-phase xenon time projection chamber. We report searches for new physics appearing through few-keV-scale electron recoils, using the experiment's first exposure of 60 live days and a fiducial mass of 5.5t. The data are found to be consistent with a background-only hypothesis, and limits are set on models for new physics including solar axion electron coupling, solar neutrino magnetic moment and millicharge, and electron couplings to galactic axion-like particles and hidden photons. Similar limits are set on weakly interacting massive particle (WIMP) dark matter producing signals through ionized atomic states from the Migdal effect.

hep-ex↗
arXiv2023

Cosmology from Cross-Correlation of ACT-DR4 CMB Lensing and DES-Y3 Cosmic Shear

Cross-correlation between weak lensing of the Cosmic Microwave Background (CMB) and weak lensing of galaxies offers a way to place robust constraints on cosmological and astrophysical parameters with reduced sensitivity to certain systematic effects affecting individual surveys. We measure the angular cross-power spectrum between the Atacama Cosmology Telescope (ACT) DR4 CMB lensing and the galaxy weak lensing measured by the Dark Energy Survey (DES) Y3 data. Our baseline analysis uses the CMB convergence map derived from ACT-DR4 and $\textit{Planck}$ data, where most of the contamination due to the thermal Sunyaev Zel'dovich effect is removed, thus avoiding important systematics in the cross-correlation. In our modelling, we consider the nuisance parameters of the photometric uncertainty, multiplicative shear bias and intrinsic alignment of galaxies. The resulting cross-power spectrum has a signal-to-noise ratio $= 7.1$ and passes a set of null tests. We use it to infer the amplitude of the fluctuations in the matter distribution ($S_8 \equiv σ_8 (Ω_{\rm m}/0.3)^{0.5} = 0.782\pm 0.059$) with informative but well-motivated priors on the nuisance parameters. We also investigate the validity of these priors by significantly relaxing them and checking the consistency of the resulting posteriors, finding them consistent, albeit only with relatively weak constraints. This cross-correlation measurement will improve significantly with the new ACT-DR6 lensing map and form a key component of the joint 6x2pt analysis between DES and ACT.

astro-ph.CO↗
arXiv2023

Search for bosonic super-weakly interacting massive particles at COSINE-100

We present results of a search for bosonic super-weakly interacting massive particles (BSW) as keV scale dark matter candidates that is based on an exposure of 97.7 kg$\cdot$year from the COSINE experiment. In this search, we employ, for the first time, Compton-like as well as absorption processes for pseudoscalar and vector BSWs. No evidence for BSWs is found in the mass range from 10 $\mathrm{keV/c}^2$ to 1 $\mathrm{MeV/c}^2$, and we present the exclusion limits on the dimensionless coupling constants to electrons $g_{ae}$ for pseudoscalar and $κ$ for vector BSWs at 90% confidence level. Our results show that these limits are improved by including the Compton-like process in masses of BSW, above $\mathcal{O}(100\,\mathrm{keV/c}^2)$.

hep-ex↗
arXiv2023

Networked Sensing for Radiation Detection, Localization, and Tracking

The detection, identification, and localization of illicit radiological and nuclear material continue to be key components of nuclear non-proliferation and nuclear security efforts around the world. Networks of radiation detectors deployed at strategic locations in urban environments have the potential to provide continuous radiological/nuclear (R/N) surveillance and provide high probabilities of intercepting threat sources. The integration of contextual information from sensors such as video, Lidar, and meteorological sensors can provide significantly enhanced situational awareness, and improved detection and localization performance through the fusion of the radiological and contextual data. In this work, we present details of our work to establish a city-scale multi-sensor network testbed for intelligent, adaptive R/N detection in urban environments, and develop new techniques that enable city-scale source detection, localization, and tracking.

physics.ins-det↗
arXiv2023

Matrix continued fractions associated with lattice paths, resolvents of difference operators, and random polynomials

We begin our analysis with the study of two collections of lattice paths in the plane, denoted $\mathcal{D}_{[n,i,j]}$ and $\mathcal{P}_{[n,i,j]}$. These paths consist of sequences of $n$ steps, where each step allows movement in three directions: upward (with a maximum displacement of $q$ units), rightward (exactly one unit), or downward (with a maximum displacement of $p$ units). The paths start from the point $(0,i)$ and end at the point $(n,j)$. In the collection $\mathcal{D}_{[n,i,j]}$, it is a crucial constraint that paths never go below the $x$-axis, while in the collection $\mathcal{P}_{[n,i,j]}$, paths have no such restriction. We assign weights to each path in both collections and introduce weight polynomials and generating series for them. Our main results demonstrate that certain matrices of size $q\times p$ associated with these generating series can be expressed as matrix continued fractions. These results extend the notable contributions previously made by P. Flajolet and G. Viennot in the scalar case $p=q=1$. The generating series can also be interpreted as resolvents of one-sided or two-sided difference operators of finite order. Additionally, we analyze a class of random banded matrices $H$, which have $p+q+1$ diagonals with entries that are independent and bounded random variables. These random variables have identical distributions along diagonals. We investigate the asymptotic behavior of the expected values of eigenvalue moments for the principal $n\times n$ truncation of $H$ as $n$ tends to infinity.

math.CO↗
arXiv2023

Evolution of plasmon excitations across the phase diagram of the cuprate superconductor La$_{2-x}$Sr$_{x}$CuO$_4$

We use resonant inelastic x-ray scattering (RIXS) at the O $K$- and Cu $K$-edges to investigate the doping- and temperature dependence of low-energy plasmon excitations in La$_{2-x}$Sr$_{x}$CuO$_4$. We observe a monotonic increase of the energy scale of the plasmons with increasing doping $x$ in the underdoped regime, whereas a saturation occurs above optimal doping $x \gtrsim 0.16$ and persists at least up to $x = 0.4$. Furthermore, we find that the plasmon excitations show only a marginal temperature dependence, and possible effects due to the superconducting transition and the onset of strange metal behavior are either absent or below the detection limit of our experiment. Taking into account the strongly correlated character of the cuprates, we show that layered $t$-$J$-$V$ model calculations accurately capture the increase of the plasmon energy in the underdoped regime. However, the computed plasmon energy continues to increase even for doping levels above $x \gtrsim 0.16$, which is distinct from the experimentally observed saturation, and reaches a broad maximum around $x = 0.55$. We discuss whether possible lattice disorder in overdoped samples, a renormalization of the electronic correlation strength at high dopings, or an increasing relevance of non-planar Cu and O orbitals could be responsible for the discrepancy between experiment and theory for doping levels above $x = 0.16$.

cond-mat.supr-con↗
arXiv2023

Revised Hamiltonian near third-integer resonance and implications for transverse resonance island buckets in storage rings

In storage rings, an accurate description of particle dynamics near third-integer resonance is crucial for various applications. The conventional approach is to extrapolate far-resonance dynamics to near-resonance, but difficulty arises because the nonlinear detuning parameter diverges at this critical point. Here we derive, via a suitable application of the canonical perturbation theory, a revised detuning parameter that is well-behaved near resonance. The resultant theory accurately describes the morphology of transverse resonance island buckets (TRIBs) for a wide range of parameter space. Our results have important implications for advanced applications of storage rings, as well as for the underlying physics of resonant particle dynamics.

physics.acc-ph↗
arXiv2023

Completeness of the NASA/IPAC Extragalactic Database (NED) -- Local Volume Sample

We introduce the NASA/IPAC Extragalactic Database (NED) Local Volume Sample (NED-LVS), a subset of $\sim$1.9 million objects with distances out to 1000~Mpc. We use UV and IR fluxes available in NED from all-sky surveys to derive physical properties, and estimate the completeness relative to the expected local luminosity density. The completeness relative to NIR luminosities (which traces a galaxy's stellar mass) is roughly 100% at $D<$30~Mpc and remains moderate (70%) out to 300~Mpc. For brighter galaxies ($\gtrsim L^{*}$), NED-LVS is $\sim$100% complete out to $\sim$400~Mpc. When compared to other local Universe samples (GLADE and HECATE), all three are $\sim$100% complete below 30~Mpc. At distances beyond $\sim$80~Mpc, NED-LVS is more complete than both GLADE and HECATE by $\sim$10-20%. NED-LVS is the underlying sample for the NED gravitational wave follow-up (NED-GWF) service, which provides prioritized lists of host candidates for GW events within minutes of alerts issued by the LIGO-Virgo-KAGRA collaboration. We test the prioritization of galaxies in the volume of GW170817 by 3 physical properties, where we find that both stellar mass and inverse specific star formation rate place the correct host galaxy in the top ten. In addition, NED-LVS can be used for a wide variety of other astrophysical studies: galaxy evolution, star formation, large-scale structure, galaxy environments, and more. The data in NED are updated regularly, and NED-LVS will be updated concurrently. Consequently, NED-LVS will continue to provide an increasingly complete sample of galaxies for a multitude of astrophysical research areas for years to come.

astro-ph.GA↗
arXiv2023

Spin-phonon interactions and magnetoelectric coupling in Co$_4$$B_2$O$_9$ ($B$ = Nb, Ta)

In order to explore the consequences of spin-orbit coupling on spin-phonon interactions in a set of chemically-similar mixed metal oxides, we measured the infrared vibrational properties of Co$_4B_2$O$_9$ ($B$ = Nb, Ta) as a function of temperature and compared our findings with lattice dynamics calculations and several different models of spin-phonon coupling. Frequency vs. temperature trends for the Co$^{2+}$ shearing mode near 150 cm$^{-1}$ reveal significant shifts across the magnetic ordering temperature that are especially large in relative terms. Bringing these results together and accounting for noncollinearity, we obtain spin-phonon coupling constants of -3.4 and -4.3 cm$^{-1}$ for Co$_4$Nb$_2$O$_9$ and the Ta analog, respectively. Analysis reveals that these coupling constants derive from interlayer (rather than intralayer) exchange interactions and that the interlayer interactions contain competing antiferromagnetic and ferromagnetic contributions. At the same time, beyond-Heisenberg terms are minimized due to fortuitous symmetry considerations, different than most other 4$d$- and 5$d$-containing oxides. Comparison with other contemporary oxides shows that spin-phonon coupling in this family of materials is among the strongest ever reported, suggesting an origin for magnetoelectric coupling.

cond-mat.mtrl-sci↗
arXiv2023

Search for solar bosonic dark matter annual modulation with COSINE-100

We present results from a search for solar bosonic dark matter using the annual modulation method with the COSINE-100 experiment. The results were interpreted considering three dark sector bosons models: solar dark photon; DFSZ and KSVZ solar axion; and Kaluza-Klein solar axion. No modulation signal that is compatible with the expected from the models was found from a data-set of 2.82 yr, using 61.3 kg of NaI(Tl) crystals. Therefore, we set a 90$\%$ confidence level upper limits for each of the three models studied. For the solar dark photon model, the most stringent mixing parameter upper limit is $1.61 \times 10^{-14}$ for dark photons with a mass of 215 eV. For the DFSZ and KSVZ solar axion, and the Kaluza-Klein axion models, the upper limits exclude axion-electron couplings, $g_{ae}$, above $1.61 \times 10^{-11}$ for axion mass below 0.2 keV; and axion-photon couplings, $g_{aγγ}$, above $1.83 \times 10^{-11}$ GeV$^{-1}$ for an axion number density of $4.07 \times 10^{13}$ cm$^{-3}$. This is the first experimental search for solar dark photons and DFSZ and KSVZ solar axions using the annual modulation method. The lower background, higher light yield and reduced threshold of NaI(Tl) crystals of the future COSINE-200 experiment are expected to enhance the sensitivity of the analysis shown in this paper. We show the sensitivities for the three models studied, considering the same search method with COSINE-200.

hep-ex↗
arXiv2023

Momentum-independent magnetic excitation continuum in the honeycomb iridate H$_3$LiIr$_2$O$_6$

In the search for realizations of Quantum Spin Liquids (QSL), it is essential to understand the interplay between inherent disorder and the correlated fluctuating spin ground state. H$_3$LiIr$_2$O$_6$ is regarded as a spin liquid proximate to the Kitaev-limit (KQSL) in which H zero-point motion and stacking faults are known to be present. Bond disorder has been invoked to account for the existence of unexpected low-energy spin excitations. Controversy remains about the nature of the underlying correlated state and if any KQSL physics survives. Here, we use resonant X-ray spectroscopies to map the collective excitations in H$_3$LiIr$_2$O$_6$ and characterize its magnetic state. We uncover a broad bandwidth and momentum-independent continuum of magnetic excitations at low temperatures that are distinct from the paramagnetic state. The center energy and high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. The absence of a momentum dependence to these excitations indicates a broken translational invariance. Our data support an interpretation of H$_3$LiIr$_2$O$_6$ as a disordered topological spin liquid in close proximity to bond-disordered versions of the KQSL. Our results shed light on how random disorder affects topological magnetic states and have implications for future experimental and theoretical works toward realizing the Kitaev model in condensed matter systems

cond-mat.str-el↗
arXiv2023

2022 report from the Auger-TA working group on UHECR arrival directions

After over 60 years, the powerful engines that accelerate ultra-high-energy cosmic rays (UHECRs) to the formidable energies at which we observe them from Earth remain mysterious. Assuming standard physics, we expect UHECR sources to lie within the local Universe (up to a few hundred~Mpc). The distribution of matter in the local Universe is anisotropic, and we expect this anisotropy to be imprinted on the distribution of UHECR arrival directions. Even though intervening intergalactic and Galactic magnetic fields deflect charged UHECRs and can distort these anisotropies, some amount of information on the distribution of the sources is preserved. In this proceedings contribution, we present the results of the joint Pierre Auger Observatory and Telescope Array searches for (a) the largest-scale anisotropies (the harmonic dipole and quadrupole) and (b) correlations with a sample of nearby starburst galaxies and the 2MRS catalogue tracing stellar mass within~250~Mpc. This analysis updates our previous results with the most recent available data, notably with the addition of 3~years of new Telescope Array data. The main finding is a correlation between the arrival directions of $12.1\%_{-3.1\%}^{+4.5\%}$~of UHECRs detected with $E \geq 38$~EeV by~Auger or with~$E \gtrsim 49$~EeV by~TA and the positions of nearby starburst galaxies on a ${15.1\text{deg}}_{-3.0\text{deg}}^{+4.6\text{deg}}$~angular scale, with a $4.7σ$~post-trial significance, up from $4.2σ$ obtained in our previous study.

astro-ph.HE↗
arXiv2023

Search for $B$ Mesogenesis at BABAR

A new mechanism has been proposed to simultaneously explain the presence of dark matter and the matter-antimatter asymmetry in the universe. This scenario predicts exotic $B$ meson decays into a baryon and a dark sector anti-baryon ($ψ_D$) with branching fractions accessible at $B$ factories. We present a search for $B \rightarrow Λψ_D$ decays using data collected by the $BABAR$ experiment at SLAC. This reaction is identified by fully reconstructing the accompanying $B$ meson and requiring the presence of a single $Λ$ baryon in the remaining particles. No significant signal is observed, and bounds on the $B \rightarrow Λψ_D$ branching fraction are derived in the range $0.13 - 5.2\times 10^{-5}$ for $1.0 < m_{ψ_D} < 4.2$ GeV/$c^{2}$. These results set strong constraints on the parameter space allowed by the theory.

hep-ex↗
arXiv2023

Observation of Kondo condensation in a degenerately doped silicon metal

When a magnetic moment is embedded in a metal, it captures itinerant electrons to form the Kondo cloud1,2, which can spread out over a few micrometres3,4. For a metal with dense magnetic impurities such that Kondo clouds overlap with each other, correlated ground states are formed. When the impurities form a regular lattice, the result is a heavy fermion or anti-ferromagnetic order depending on the dominant interaction5,6. Even in the case of random impurities, overlapping Kondo clouds are expected to form a coherent ground state. Here, we examine this issue by performing electrical transport and high-precision tunnelling density-of-states (DOS) spectroscopy measurements in a highly P-doped crystalline silicon metal where disorder-induced localized magnetic moments exist7. We detect the Kondo effect in the resistivity of the Si metal below 2 K and an exotic pseudogap in the DOS with gap edge peaks at a Fermi energy below 100 mK. The DOS gap and peaks are tuned by applying an external magnetic field and transformed into a metallic Altshuler-Aronov gap8 in the paramagnetic disordered Fermi liquid (DFL) phase. We interpret this phenomenon as the Kondo condensation, the formation of a correlated ground state of overlapping Kondo clouds, and its transition to a DFL. The boundary between the Kondo condensation and DFL phases is identified by analysing distinct DOS spectra in the magnetic field-temperature plane. A detailed theoretical analysis using a holographic method 9 , 10 , 11 reproduces the unusual DOS spectra, 1, supporting our scenario. Our work demonstrates the observation of the magnetic version of Bardeen-Cooper-Shrieffer (BCS) pair condensation and will be useful for understanding complex Kondo systems.

cond-mat.str-el↗
arXiv2022

Three-year annual modulation search with COSINE-100

COSINE-100 is a direct detection dark matter experiment that aims to test DAMA/LIBRA's claim of dark matter discovery by searching for a dark matter-induced annual modulation signal with NaI(Tl) detectors. We present new constraints on the annual modulation signal from a dataset with a 2.82 yr livetime utilizing an active mass of 61.3 kg, for a total exposure of 173 kg$\cdot$yr. This new result features an improved event selection that allows for both lowering the energy threshold to 1 keV and a more precise time-dependent background model. In the 1-6 keV and 2-6 keV energy intervals, we observe best-fit values for the modulation amplitude of 0.0067$\pm$0.0042 and 0.0051$\pm$0.0047 counts/(day$\cdot$kg$\cdot$keV), respectively, with a phase fixed at 152.5 days.

hep-ex↗
arXiv2022

Solid State Detectors and Tracking for Snowmass

Tracking detectors are of vital importance for collider-based high energy physics (HEP) experiments. The primary purpose of tracking detectors is the precise reconstruction of charged particle trajectories and the reconstruction of secondary vertices. The performance requirements from the community posed by the future collider experiments require an evolution of tracking systems, necessitating the development of new techniques, materials and technologies in order to fully exploit their physics potential. In this article we summarize the discussions and conclusions of the 2022 Snowmass Instrumentation Frontier subgroup on Solid State and Tracking Detectors (Snowmass IF03).

physics.ins-det↗
arXiv2022

Input optics systems of the KAGRA detector during O3GK

KAGRA, the underground and cryogenic gravitational-wave detector, was operated for its solo observation from February 25th to March 10th, 2020, and its first joint observation with the GEO 600 detector from April 7th -- 21st, 2020 (O3GK). This study presents an overview of the input optics systems of the KAGRA detector, which consist of various optical systems, such as a laser source, its intensity and frequency stabilization systems, modulators, a Faraday isolator, mode-matching telescopes, and a high-power beam dump. These optics were successfully delivered to the KAGRA interferometer and operated stably during the observations. The laser frequency noise was observed to limit the detector sensitivity above a few kHz, whereas the laser intensity did not significantly limit the detector sensitivity.

gr-qc↗
arXiv2022

Radon concentration variations at the Yangyang underground laboratory

The concentration of radon in the air has been measured in the 700 m-deep Yangyang underground laboratory between October 2004 and May 2022. The average concentrations in two experimental areas, called A6 and A5, were measured to be 53.4$\pm$0.2 Bq/m3 and 33.5$\pm$0.1 Bq/m3, respectively. The lower value in the A5 area reflects the presence of better temperature control and ventilation. The radon concentrations sampled within the two A5 experimental rooms' air are found to be correlated to the local surface temperature outside of the rooms, with correlation coefficients r = 0.22 and r = 0.70. Therefore, the radon concentrations display a seasonal variation, because the local temperature driven by the overground season influences air ventilation in the experimental areas. A fit on the annual residual concentrations finds that the amplitude occurs each year on August, 31$\pm$6 days.

physics.ins-det↗