arXiv subjects

Byung-Geel Yu

Publications and source records attributed to Byung-Geel Yu.

At least 19 recordsLinked to original sources

arXiv2026

Effective Color Dipole Approach to Color Transparency in $\rho^0$ Electroproduction

We investigate nuclear transparency in exclusive $\rho^0$ electroproduction on $^{12}$C and $^{56}$Fe nuclei within a multi-channel final-state interaction (FSI) framework that explicitly incorporates the kinematic decay length effect (DLE) arising from the short-lived $\rho^0\to\pi^+\pi^-$ decay. The purely kinematic and nuclear mechanisms prove insufficient to account for the CLAS data: the DLE alone cannot generate the observed $Q^2$-dependent enhancement, and the inclusion of nuclear shadowing further deepens the disagreement, so that a compensating reduction of the in-medium attenuation -- the hallmark of color transparency (CT) -- is required. To incorporate the color dynamics of the initially compact $q\bar{q}$ configuration, we replace the empirical Quantum Diffusion Model (QDM) ansatz for the initial interaction cross section $\sigma_h(Q^2)$ of the point-like configuration (PLC) by an effective Color Dipole Model (CDM) boundary condition, evaluated through a normalized dipole-weighted $\gamma^*\to\rho^0$ transition overlap. Combined with the standard linear QDM transport at an effective in-medium expansion scale $\Delta m^2 = 0.3$~GeV$^2$, the CDM boundary condition reproduces both the magnitude and the $Q^2$ dependence of the data for both targets. A $\chi^2$ analysis quantifies the pronounced separation between the non-CT and CT-based descriptions and thereby supports the onset of color transparency in the $\rho^0$ channel beyond what kinematic decay-length effects can accommodate.

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arXiv2026

Non-universality of color transparency onset in pion and kaon electroproduction

A combined analysis of the Jefferson Lab data on nuclear transparency in $A(e,e'\pi^+)$ and $A(e,e'K^+)$ shows that the onset of color transparency (CT) is not universal across meson flavors. The pion transparency is well reproduced by the standard quantum diffusion model (QDM) with $\Delta M^2_\pi \simeq 0.7$ GeV$^2$, whereas the kaon data favor the quadratic expansion of the naive parton model (NPM) with the natural hadronic scale $R_K \sim \sqrt{\sigma_{KN}/\pi}$. This dichotomy cannot be repaired by physically motivated parameter choices: the pion slope excludes the quadratic expansion with any physical radius, and the kaon slope requires a QDM excitation scale far below the range conventionally used in pion transparency analyses. A microscopic interpretation, in which the diffusive evolution of the pion appears as an exceptional consequence of its Goldstone-boson nature while the kaon follows the generic ballistic expansion, is discussed.

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arXiv2025

Naive parton picture for kaon color transparency in $A(e,e'K^+)$

Nuclear transparency in the electronuclear reaction $A(e,e'K^+)$ is investigated in parallel with our previous study of pion transparency in Phys.\ Rev.\ C {\bf 111}, 064608 (2025). Based on an extended Glauber framework that incorporates shadowing from the initial-state two-step process, kaon color transparency (CT) is analyzed to show that the steeper $Q^2$ dependence observed for kaon CT, compared with the pion case, is more naturally described by the naive parton model (NPM) than by the quantum diffusion model (QDM). The inclusion of initial-state shadowing further reduces the transparency and improves the agreement with the experimental data. The $Q^2$ and $A$ dependences of the kaon transparency are presented up to $Q^2=10$~GeV$^2/c^2$, together with the corresponding $\alpha(Q^2)$ and the supplementary ratio $T_A/T_C$, for comparison with the Jefferson Lab (JLab) data obtained with the 6-GeV electron beam on $^{12}$C, $^{63}$Cu, and $^{197}$Au nuclei.

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arXiv2024

Revisiting $KN$ elastic and charge exchange reactions in search of the pentaquark $\Theta^+$ baryon

In the search for the pentaquark $\Theta^+$ baryon, the world data on $K^+n\to K^+n$ and $K^+n\to K^0\,p$ reactions on the deuteron target and $K^0\,p\to K^+n$ and $K^0_L\,p\to K^0_S\,p$ reactions on the hydrogen target are revisited to study the isoscalar component of the scattering amplitudes. The determination of the $s$- and $p$-wave phase shifts for the two former channels on the deuteron target is presented in the low momentum region with the uncertainty due to the deuteron form factors at forward angles discussed. For the reactions on hydrogen targets, a similarity expected from time reversal between the charge exchange processes $K^+n\to K^0\,p$ and $K^0\,p\to K^+n$ is exploited, while we present the analysis of the $K_L^0\,p\to K_S^0\,p$ scattering based on the $s$-wave phase shift for low momenta combined with the $t$-channel $\rho^0(775)+\omega(782)+\phi(1020)$ vector meson exchange at high momenta. With the mass 1535 MeV and decay width 5 MeV the possibility of the $\Theta^+$ in the Breit-Wigner (BW) form is tested in the differential cross section measured by C. J. S. Damerell {\it et\ al.} at ${\rm P_{Lab}}=434$ MeV/$c$ and polarization. Our analysis suggests measuring the polarization observable rather than the differential cross section, which has sufficient sensitivity to distinguish the $\Theta^+$ baryon among all spin and parity states $J^P = 1/2^\pm$ and $3/2^\pm$.

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arXiv2024

Nuclear transparency and shadowing of the two-step process in the $A(e,e'\pi^+)$ reaction

We investigate nuclear transparency induced by pion electroproduction on nuclei, $A(e,e'\pi^+)$, with our interest in the role of the two-step process in the Glauber multiple scattering theory. Based on the framework in which the quantum diffusion model is incorporated into the Glauber theory, the experimental data in the range of photon virtuality $0.5< Q^2< 10$ GeV$^2/c^2$ are analyzed, including the recent JLab data at the 6 GeV electron beam together with the proposal for the 12 GeV upgrade. Application of the quantum diffusion model during the formation length of the quark/antiquark $(q\bar{q})$ structure of a pion reproduces the increase in the nuclear transparency up to high $Q^2$, showing evidence of color transparency. In contrast, through the coherent length of the $\gamma^*$ fluctuation into $\rho^0$, the two-step process with the $\rho N$ scattering cross section chosen to be $\sigma_{\rho N}=\sigma_{\pi N}$ contributes to a reduction of the nuclear transparency in the whole range of $Q^2$. Combined with the one-step process (direct photon coupling) usually adopted in the original formulation of the Glauber theory, this reaction mechanism provides another source of the $Q^2$ dependence of the transparency at low virtualities through the shadowing in the initial state interaction. By the further absorption due to the shadowing, a better agreement is obtained with the pion transparency measured in the $A(e,e'\pi^+)$ reaction for $^{12}$C, $^{27}$Al, $^{63}$Cu, and $^{197}$Au nuclei. A discussion of the $Q^2$ dependence of the parameter $\alpha$ for the transparency $T_A=A^{\alpha-1}$ is given.

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arXiv2022

Pseudoscalar and Scalar Meson Photoproduction Interpreted by Regge Phenomenology

We have evaluated pseudoscalar and scalar neutral pion photoproduction in $\vec{\gamma}p\to\pi^0p$ and $\vec{\gamma}p\to a_0^0p$ above the resonance region and within Regge phenomenology. Our fit, including GlueX $\Sigma$ pseudoscalar photoproduction data, shows that previous SLAC $\Sigma$ measurements for $\vec{\gamma}p \to \pi^0p$ above $E_\gamma = 4~\mathrm{GeV}$ are at variance with SLAC data with more recent measurements made by GlueX in vicinity of $E_\gamma = 9~\mathrm{GeV}$. The Regge model predicts that the beam polarization asymmetry $\Sigma$ of the scalar meson is opposite to that of pseudoscalar meson photoproduction, however, the cross sections are similar. While the vector natural parity meson exchange is dominant in both cases, the contribution of the pseudovector unnatural parity meson exchange is very small. Using Regge phenomenology, we predicted high energy behavior for double polarized observables $\mathbb{E}$, $\mathbb{F}$, $\mathbb{G}$, and $\mathbb{H}$ for the reactions $\gamma p\to \pi^0p$ and $\gamma p\to a_0^0p$.

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arXiv2021

Partial wave analysis of $K^+N$ scattering and the possibility of pentaquark $\Theta^+(1540)$

Elastic $K^+ n\to K^+ n$ and charge exchange $K^+n\to K^0p$ reactions at low momenta are investigated using the partial wave analysis. Isospin relation gives constrains for the partial $s$- and $p$-waves among elastic $K^+p$, $K^+n$ and charge exchange $K^+n\to K^0p$ amplitudes. Two sets of the phase shift for these partial waves in the isoscalar channel are obtained from the fit of experimental data on total and differential cross sections. Polarization observable leads to a good criterion to decide which set is valid. Differential cross section data near $P_{\rm Lab}=434$ MeV/$c$ suggests a possibility of a resonance, e.g., the exotic $\Theta^+(1540)$ baryon around $\sqrt{s}\simeq$ 1.54GeV.

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arXiv2019

Photoproductions of $f_1(1285)$ and $\eta'(958)$ from the analysis of CLAS data with the Primakoff effect at high energies

We investigate photoproduction of axial vector meson $f_1(1285)$ based on the CLAS experiment $\gamma p\to pf_1(1285)\to p\eta\pi^+\pi^-$ using the Regge model for $\rho^0+\omega$ exchanges. The combined analysis of $\gamma p\to p\eta'\to p\eta\pi^+\pi^-$ reaction including $\eta(1295)$ is accompanied to evaluate the decay mode $\eta(1295)\to \eta\pi^+\pi^-$ from the potential overlap with the $f_1$ reaction. The predominance of $\rho^0(770)$ exchange over the $\omega(782)$ with the coupling constant $\gamma\rho^0f_1$ extracted from the CLAS experiment leads to a good description of the measured cross sections for $f_1$, while the scale of the cross section is corrected by the branching fraction $\eta'\to\eta\pi^+\pi^-$, and $f_1\to\eta\pi^+\pi^-$, respectively. As an extension to study the nonmesonic production mechanism, the Primakoff effect by the virtual photon exchange is investigated in the exclusive reaction $\gamma p\to pf_1$ up to $\sqrt{s}\approx50$ GeV, finding that it plays a similar role to the Pomeron in the vector meson photoproduction at high energies. Such an unique role of the virtual photon exchange similar to the $f_1$ case is identified up to $\sqrt{s}\approx250$ GeV in the $\gamma p\to p\pi^0$ and $\gamma p\to p\eta$ as well as $\gamma p\to p\eta'$ reaction.

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arXiv2019

A new combined analysis of elastic and charge exchange $K N(\bar{K}N)$ scatterings in the Regge realm

The Regge features of elastic $K^\pm N\to K^\pm N$, and charge exchange $K^-p\to\bar{K}^0n$ and $K^+n\to K^0p$ reactions are described by using a combined analysis of all these channels at high momenta. Based on the meson exchanges in the $t$-channel with their decays to $K\bar{K}$ pair allowed, the exchanges of $\rho(775)+\omega(782)$ are excluded in contrast to existing model calculations and the present work follows a new scheme for the meson exchanges $a_0(980)+\phi(1020)+f_2(1275)+a_2(1320)$ reggeized for the forward elastic scattering amplitude together with Pomeron. The charge exchange reactions are described by $a_0(980)+a_2(1320)$ exchanges in the $t$-channel. Dominance of the isoscalar $f_2$ and Pomeron exchanges beyond $P_{\rm Lab}\approx3$ GeV/$c$ is shown in the elastic process. Both the isovector $a_0$ and $a_2$ exchanges in charge exchange reactions play the respective roles in the low and high momentum region. Differential and total cross sections are presented to compare with existing data. Discussion is given to the polarization of $K^-p\to K^-p$ at $P_{Lab}=10$ GeV/$c$ and $K^-p\to \bar{K}^0n$ at $P_{Lab}=$ 8 GeV/$c$.

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arXiv2018

Features of $\omega$ photoproduction off proton target at backward angles : Role of nucleon Reggeon in $u$-channel with parton contributions

Backward photoproduction of $\omega$ off a proton target is investigated in a Reggeized model where the $u$-channel nucleon Reggeon is constructed from the nucleon Born terms in a gauge invariant way. The $t$-channel meson exchanges are considered as a background. While the $N_\alpha$ trajectory of the nucleon Reggeon reproduces the overall shape of NINA data measured at the Daresbury Laboratory in the range of $u$-channel momentum transfer squared $-1.7<u<0.02$ GeV$^2$ and energies at $E_\gamma=2.8$, 3.5 and 4.7 GeV, a possibility of parton contributions is searched for through the nucleon isoscalar form factor which is parameterized in terms of parton distributions at the $\omega NN$ vertex. Detailed analysis is presented for NINA data to understand the reaction mechanism that could fill up the deep dip from the nucleon Reggeon at momentum squared $u=-0.15$ GeV$^2$. The angle dependence of differential cross sections at the NINA energies above are reproduced in the overall range of $u$ including the CLAS data at forward angles in addition. The energy dependence of the differential cross section is investigated based on the NINA data and the recent LEPS data. A feature of the present approach that implicates parton contributions via nucleon form factor is illustrated in the total and differential cross sections provided by GRAAL and CB-ELSA Collaborations.

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arXiv2018

Features of forward $\pi N$ scattering from a Reggeized model

Charge exchange process $\pi^-p\to\pi^0n$ and elastic scatterings $\pi^\pm p\to \pi^\pm p$ are investigated within the Regge framework where the relativistic Born amplitude is reggeized for the $t$-channel meson exchange. Charge exchange cross section is featured by the single $\rho$ exchange. Additional correction by Regge cuts, $\rho$-$f_2$ and $\rho$-Pomeron, agree with differential cross sections and new trajectory for the $\rho'(1450)$ exchange is attempted to reproduce polarization data. For the description of elastic scattering data up to pion momentum $P_{\rm Lab}\approx 250$ GeV/c, Pomeron exchange of the Donnachie-Landshoff type is newly constructed and applied in this work. Elastic cross section data are well reproduced with the dominance of $f_2$ and Pomeron exchanges in intermediate and high energies. Analysis of nucleon resonances is presented to test the validity of the present Regge framework below $W\leq2$ GeV.

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arXiv2017

Features of $\omega$ photoproduction off nucleon target at forward angles : Dominance of $\pi$ exchange with Regge cuts and scaling of differential cross sections

We investigate photoproduction of $\omega$ off a nucleon target $\gamma N\to\omega N$ by using a Reggeized model where $\pi(135)+\sigma(500)+f_1(1285)+f_2(1270)$+Pomeron exchanges are included in the $t$-channel for the reaction at forward angles. The reaction mechanism at low energy is featured by the dominance of the $\pi$ exchange with the absorptive cuts introduced to modulate the pion contribution to both $\gamma p\to \omega p$ and $\gamma n\to \omega n$ reactions. Necessity of $\sigma$ exchange is illustrated in the analysis of the cross section from natural parity exchanges. Cross sections for differential, total, and spin density matrix with beam polarization are reproduced and compared with existing data on $\gamma p\to \omega p$. Scaled differential cross sections of Jefferson Lab data on $\gamma p\to \omega p$ are investigated at the production angle $\theta=90^\circ$ with the nonlinear trajectories for a saturation. Differential and total cross sections for the $\gamma n\to\omega n$ reaction are analyzed to compare with recent experimental data at the CBELSA/TAPS Collaboration. An application to the $\gamma p\to\omega\Delta^+$ reaction is presented to demonstrate the significance of the $\pi$ exchange in the total and differential cross sections.

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arXiv2017

Regge phenomenology of photoproduction of $\pi^-\Delta^{++}$ and scaling with saturation of trajectory

In this work we investigate the reaction $\gamma p\to\pi^-\Delta^{++}$ in the Reggeized model for $\pi(138)+\rho(775)+a_2(1320)$ exchanges in the $t$-channel. For a convergence of the reaction cross section at high energies the minimal forms of proton and $\Delta^{++}$ exchanges are introduced in the direct and crossed channels for gauge invariance of $\pi$ Regge-pole exchange. The role of spin-2 tensor meson $a_2$ is found to be crucial to agree with existing data at high energies. Electromagnetic multipoles of $\Delta^{++}$ baryon are analyzed in the $\Delta$ resonance region. Based on the constituents counting rule the scaled differential cross section at $E_\gamma=4$ GeV is reproduced with the Regge trajectory saturated at large momentum transfer $-t$.

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arXiv2017

Photoproduction of ${\gamma p\to K^+\Lambda^(1520)}$ and decay of $\Lambda^(1520)\to K^- p$ in the Reggeized framework

Photoproduction of the $\Lambda^*(1520)$ resonance of spin-parity ${3\over2}^-$ off the proton target is investigated within the Regge framework where the $t$-channel reggeization is applied for the $K(494)+K^*(892)+K_2^*(1430)$ exchanges in the Born amplitude. The present model is based on the two basic ingredients; the one is the minimal gauge prescription for the convergence of the reaction and the other is the role of the $K_2^*$ crucial to be consistent with high energy data. The cross sections for the total, differential and photon polarization asymmetry are reproduced without fit parameters and compared with existing data. The LAMP2 and LEPS measurements of the angular distribution of the $K^-$ in the $\Lambda^*(1520)\to K^-p$ decay are investigated and found to be dominated by the decay of $\Lambda^*$ with helicity $\pm3/2$ based on the analysis of the density matrix elements related. Detailed discussion on the density matrix elements is given to clarify the analysis of the observable. The reaction mechanism is featured by the dominance of the contact term with the $K$ and $K_2^*$ exchanges following in the low energy region. The $K^*$ exchange appears in minor role. At high energies beyond $E_\gamma\approx 5$ GeV the role of $K_2^*$ exchange leads over other exchanges in the reaction process.

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arXiv2017

Photoproduction of $\gamma N\to K^+ \Sigma^*(1385)$ in the Reggeized framework

Photoproduction of $ K\Sigma^{*}(1385)$ on the nucleon is investigated within the Regge framework and the reaction mechanism is analyzed based on the data existing in the channels $\gamma p\to K^+\Sigma^{*0}$ and $\gamma n\to K^+\Sigma^{*-}$. The Reggeization of the $t$-channel meson exchanges $K(494)+K^*(892)+K_2^*(1430)$ is employed to construct the photoproduction amplitude. The Rarita-Schwinger formalism is applied for the spin-3/2$^+$ strangeness-baryon $\Sigma^*$ with a special gauge prescription utilized for the convergence of these reaction processes. Within a set of coupling constants determined from the symmetry arguement for the $K$ and $K^*$ and from the duality and vector dominance for the $K_2^*$, the data of the both processes are reproduced to a good degree. The production mechanism of these processes are featured by the dominance of the contact term plus the $K$ exchange with the role of the $K_2^*$ following rather than the $K^*$.

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arXiv2016

Reggeized model for $\gamma p \to \rho^- \Delta^{++}(1232)$ photoproduction

A model for the reaction $\gamma p\to\rho^-\Delta^{++}$ is presented with the $t$-channel $\pi+\rho$ exchanges reggeized to describe the reaction up to high energies. Gauge invariance of $\rho$ exchange is discussed in connection with the convergence of the reaction cross section at high energy. The roles of electromagnetic (EM) multipole moments of $\Delta^{++}$ baryon and of $\rho^-$ meson are analyzed in total and differential cross sections and spin density matrix elements. Photon polarization asymmetry $\Sigma$ is predicted for a measurement of electromagnetic moments of $\rho^-$ and of $\Delta^{++}$.

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arXiv2016

Investigating convergence of the reaction $\gamma p\to\pi^\pm\Delta$ and tensor meson $a_2$ exchange at high energy

A Regge approach to the reaction processes $\gamma p\to\pi^-\Delta^{++}$ and $\gamma p\to\pi^+\Delta^0$ is presented for the description of existing data up to $E_\gamma= 16$ GeV. The model consists of the $t$-channel $\pi(139)+\rho(775)+a_2(1320)$ exchanges which are reggeized from the relevant Born amplitude. Discussion is given on the minimal gauge prescription for the $\pi$ exchange to render convergent the divergence of the $u$-channel $\Delta$-pole in the former process. A new Lagrangian is constructed for the $a_2N\Delta$ coupling in this work and applied to the process for the first time with the coupling constant deduced from the duality plus vector dominance. It is shown that, while the $\pi$ exchange dominates over the process, the role of the $a_2$ exchange is crucial rather than the $\rho$ in reproducing the cross sections for total, differential, and photon polarization asymmetry to agree with data at high energy.

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arXiv2016

Role of $\sigma$ exchange in the $\gamma p\to \phi p$ process and scaling with the $f_1$ axial vector meson from a Reggeized model

We investigate the role driven by the scalar meson $\sigma$ exchange in the photoproduction of the vector meson $\phi$(1020) off a proton by using a Reggeized model. Based on the $\pi^0(135)+\sigma(500)+f_2(1270)$+Pomeron exchanges, we demonstrate that the $\sigma$ exchange plays the role to reproduce the bump structure at the forward angle in the differential cross section as well as the peaking behavior in the total cross section observed in the CLAS Collaboration. We also discuss the possible observation of the scaled cross section $s^7d\sigma /dt$ at the production angle $\theta=90^{\circ}$ from the CLAS data. It is found that the axial vector meson $f_1(1285)$ exchange with the trajectory $\alpha_{f_1}(t)=0.028\,t+0.9\pm0.2$ arising from the axial anomaly of the QCD vacuum plays the role to clarify the scaling up to 5 GeV.

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