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C. W. Kim

Publications and source records attributed to C. W. Kim.

At least 19 recordsLinked to original sources
arXiv2025

Optimal Characteristics of Inspection Vehicle for Drive-by Bridge Inspection

Drive-by inspection for bridge health monitoring has gained increasing attention over the past decade. This method involves analysing the coupled vehicle-bridge response, recorded by an instrumented inspection vehicle, to assess structural integrity and detect damage. However, the vehicles mechanical and dynamic properties significantly influence detection performance, limiting the effectiveness of the approach. This study presents a framework for optimising the inspection vehicle to enhance damage sensitivity. An unsupervised deep learning methodbased on adversarial autoencoders (AAE)is used to reconstruct the frequency-domain representation of acceleration responses. The mass and stiffness of the tyre suspension system of a two-axle vehicle are optimised by minimising the Wasserstein distance between damage index distributions for healthy and damaged bridge states. A Kriging meta-model is employed to approximate this objective function efficiently and identify optimal vehicle configurations in both dimensional and non-dimensional parameter spaces. Results show that vehicles with frequency ratios between 0.3 and 0.7 relative to the bridges' first natural frequency are most effective, while those near resonance perform poorly. Lighter vehicles require lower natural frequencies for optimal detection. This is the first study to rigorously optimise the sensing platform for drive-by sensing and to propose a purpose-built inspection vehicle.

cs.LG↗
arXiv2022

Measurement of the proton spin structure at long distances

Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV$^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.

nucl-ex↗
arXiv2020

Photoproduction of $η$ mesons off the proton for $1.2 < E_γ< 4.7$ GeV using CLAS at Jefferson Laboratory

Photoproduction cross sections are reported for the reaction $γp\to pη$ using energy-tagged photons and the CLAS spectrometer at Jefferson Laboratory. The $η$ mesons are detected in their dominant charged decay mode, $η\to π^+π^-π^0$, and results on differential cross sections are presented for incident photon energies between 1.2 and 4.7 GeV. These new $η$ photoproduction data are consistent with earlier CLAS results but extend the energy range beyond the nucleon resonance region into the Regge regime. The normalized angular distributions are also compared with the experimental results from several other experiments, and with predictions of $η$ MAID\,2018 and the latest solution of the Bonn-Gatchina coupled-channel analysis. Differential cross sections $dσ/dt$ are presented for incident photon energies $E_γ> 2.9$ GeV ($W > 2.5$ GeV), and compared with predictions which are based on Regge trajectories exchange in the $t$-channel (Regge models). The data confirm the expected dominance of $ρ$, $ω$ vector-meson exchange in an analysis by the Joint Physics Analysis Center.

nucl-ex↗
arXiv2020

Probing the core of the strong nuclear interaction

The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of Quantum Chromodynamics (QCD). However, as these equations cannot be solved directly, physicists resort to describing nuclear interactions using effective models that are well constrained at typical inter-nucleon distances in nuclei but not at shorter distances. This limits our ability to describe high-density nuclear matter such as in the cores of neutron stars. Here we use high-energy electron scattering measurements that isolate nucleon pairs in short-distance, high-momentum configurations thereby accessing a kinematical regime that has not been previously explored by experiments, corresponding to relative momenta above 400 MeV/c. As the relative momentum between two nucleons increases and their separation thereby decreases, we observe a transition from a spin-dependent tensor-force to a predominantly spin-independent scalar-force. These results demonstrate the power of using such measurements to study the nuclear interaction at short-distances and also support the use of point-like nucleons with two- and three-body effective interactions to describe nuclear systems up to densities several times higher than the central density of atomic nuclei.

nucl-ex↗
arXiv2020

Beam spin asymmetry in semi-inclusive electroproduction of a hadron pair

A first measurement of the longitudinal beam spin asymmetry ALU in the semi-inclusive electroproduction of pairs of charged pions is reported. ALU is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498 GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the sin(phiR) moments of ALU are extracted for the kinematic variables of interest in the valence quark region. The understanding of di-hadron production is essential for the interpretation of observables in single hadron production in semi-inclusive DIS, and pioneering measurements of single spin asymmetries in di-hadron production open a new avenue in studies of QCD dynamics.

hep-ex↗
arXiv2020

Extraction of beam-spin asymmetries from the hard exclusive $π^{+}$ channel off protons in a wide range of kinematics

We have measured beam-spin asymmetries to extract the $\sinϕ$ moment $A_{LU}^{\sinϕ}$ from the hard exclusive $\vec{e} p \to e^\prime n π^+$ reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center-of-mass. The $A_{LU}^{\sinϕ}$ moment has been measured up to 6.6 GeV$^{2}$ in $-t$, covering the kinematic regimes of Generalized Parton Distributions (GPD) and baryon-to-meson Transition Distribution Amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found $A_{LU}^{\sinϕ}$ to be negative, while a sign change was observed near 90$^\circ$ in the center-of-mass. The unique results presented in this paper will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks.

nucl-ex↗
arXiv2019

Exploring the Structure of the Bound Proton with Deeply Virtual Compton Scattering

In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correlations between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this work, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering (DVCS) off a proton bound in $^4$He. The data used here were accumulated using a $6$ GeV longitudinally polarized electron beam incident on a pressurized $^4$He gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle ($ϕ$) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The $Q^2$, $x_B$, and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20\% to 40\%, indicating possible medium modification of its partonic structure.

nucl-ex↗
arXiv2000

Quantum Mechanics of Neutrino Oscillations

We present a simple but general treatment of neutrino oscillations in the framework of quantum mechanics using plane waves and intuitive wave packet principles when necessary. We attempt to clarify some confusing statements that have recently appeared in the literature.

hep-ph↗
arXiv2000

Finally neutrino has mass

The present status of the problem of neutrino mass, mixing and neutrino oscillations is briefly summarized. The evidence for oscillations of atmospheric neutrinos found recently in the Super-Kamiokande experiment is discussed. Indications in favor of neutrino oscillations obtained in solar neutrino experiments and in the accelerator LSND experiment are also considered. Implications of existing neutrino oscillation data for neutrino masses and mixing are discussed.

hep-ph↗
arXiv1999

Full Numerical Estimation of Neutrino Mixing Parameters from Solar Neutrino Data

We have numerically computed survival probabilities of solar neutrinos interacting with matter via MSW mechanism in the full three generation formalism with $Δm^2_{23}=2.2\times 10^{-3}$ eV$^2$. For $θ_{13} \lesssim 30^{\circ}$, we confirm the two regions found in the two generation case, (1) with the most likelyhood, small $\sin^2(2θ_{12}) \sim 0.006$, (2) with less likelyhood, large $\sin^2(2θ_{12}) \gtrsim 0.5$. For $θ_{13}\gtrsim 30^{\circ}$, we find an additional region, (3) with even less likelyhood, $10^{-5} < Δm^2_{12}< 10^{-4}$ eV$^2$ and/or $10^{-4} < \sin^2(2θ_{12}) < 0.5$. Assuming that the case (1) is valid, we predict that $θ_{13} \simeq 15^\circ$.

hep-ph↗
arXiv1999

Heavy Majorana neutrinos in e+e- colliders

We investigate possibilities for detecting heavy Majorana neutrinos ($N$'s) in $e^+e^-$ at LEP200 and future Linear Colliders. We concentrate on the processes where the pairs of intermediate heavy $N$'s produce a clear signal of total lepton number violation ($e^+e^- \to NN \to W^+l^-W^+l^{\prime -}$). Such a signal is not possible if the heavy neutrinos are of Dirac nature. Our approach is general in the sense that the intermediate $N$'s can be either on shell or off shell. Discussion of the relative numerical importance of the $s$ and the $t+u$ channels of the $NN$ production is also included.

hep-ph↗
arXiv1999

Supersymmetric Neutrino Masses and Mixing with R-parity Violation

In the context of the minimal supersymmetric standard model, nonzero neutrino masses and mixing can be generated through renormalizable lepton number (and thus R-parity) violating operators. It is examined whether neutrino mass matrices from tree and one-loop contributions can account for two mass-squared differences and mixing angles that explain current experimental data. By accommodating, in particular, the solar and atmospheric neutrino data, we find interesting restrictions not only on the free parameters of the theory, such as lepton number violating couplings and soft-parameters, but also on the oscillation parameters of atmospheric neutrinos.

hep-ph↗
arXiv1999

Implications of Super-Kamiokande atmospheric low-energy data for solar neutrino oscillations

It is shown that the high-Delta m^2 part of the large mixing angle MSW solution of the solar neutrino problem is disfavored by the Super-Kamiokande data for low-energy upward-going events. A quantitative bound is obtained in the three-neutrino scheme with a negligibly small element U_{e3} of the neutrino mixing matrix, as indicated by the result of the CHOOZ long-baseline antinu_e->antinu_e oscillation experiment.

hep-ph↗
arXiv1998

Comment on the possible electron neutrino excess in the Super-Kamiokande atmospheric neutrino experiment

We investigate the implications of a possible excess of the electron neutrino events in the Super-Kamiokande atmospheric neutrino experiment. The excess, if real, leads to constraints on the $ν_μ\leftrightarrow ν_e$, $ν_μ\leftrightarrow ν_τ$ and $ν_e \leftrightarrow ν_τ$ oscillation parameters. Specifically, the excess impies that $ν_e - ν_μ$ and $ν_μ- ν_τ$ mixings are large and $ν_e - ν_τ$ mixing is small. We show that the electron neutrino excess favors the large mixing angle MSW solution of the solar neutrino problem.

hep-ph↗
arXiv1998

Atmospheric neutrino oscillations with three neutrinos and a mass hierarchy

A comprehensive formalism for the description of neutrino oscillations in the Earth in a general scheme with three massive neutrinos and the mass hierarchy m_1< nu_e, nu_mu<->nu_tau, nu_e<->nu_tau) could be large. Hence, long-baseline experiments with reactor (CHOOZ and Palo Verde) and accelerator (K2K, MINOS and ICARUS) neutrinos could observe neutrino oscillations in all channels with a relatively large statistics.

hep-ph↗
arXiv1998

Three Neutrino $Δm^2$ scales and Singular Seesaw Mechanism

It is shown that the singular seesaw mechanism can simultaneously explain all the existing data supporting nonzero neutrino masses and mixing. The three mass-squared differences that are needed to accommodate the atmospheric neutrino data (through $ν_μ- ν_s$ oscillation), the solar neutrino data via MSW mechanism (through $ν_e - ν_τ$ oscillation), and the positive result of $ν_μ- ν_e$ oscillation from LSND can be generated by this mechanism, whereas the vacuum oscillation solution to the solar neutrino problem is disfavored. We find that the electron and tau neutrino masses are of order $10^{-3}$ eV, and the muon neutrino and a sterile neutrino are almost maximally mixed to give a mass of order 1 eV. Two heavy sterile neutrinos have a mass of order 1 keV which can be obtained by the double seesaw mechanism with an intermediate mass scale $\sim 10^5$ GeV. A possible origin of such a scale is discussed.

hep-ph↗
arXiv1998

Coherence of neutrino oscillations in the wave packet approach

The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov and Weiss that an accurate measurement of the energies of the particles participating in the detection process can increase the coherence length. However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost.

hep-ph↗