arXiv subjects

Tae Keun Choi

Publications and source records attributed to Tae Keun Choi.

13 recordsLinked to original sources

arXiv2026

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

A combined analysis of the Jefferson Lab data on nuclear transparency in $A(e,e'π^+)$ 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 $ΔM^2_π\simeq 0.7$ GeV$^2$, whereas the kaon data favor the quadratic expansion of the naive parton model (NPM) with the natural hadronic scale $R_K \sim \sqrt{σ_{KN}/π}$. 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.

hep-ph↗

arXiv2026

Effective Color Dipole Approach to Color Transparency in $ρ^0$ Electroproduction

We investigate nuclear transparency in exclusive $ρ^0$ 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 $ρ^0\toπ^+π^-$ 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 $σ_h(Q^2)$ of the point-like configuration (PLC) by an effective Color Dipole Model (CDM) boundary condition, evaluated through a normalized dipole-weighted $γ^*\toρ^0$ transition overlap. Combined with the standard linear QDM transport at an effective in-medium expansion scale $Δm^2 = 0.3$~GeV$^2$, the CDM boundary condition reproduces both the magnitude and the $Q^2$ dependence of the data for both targets. A $χ^2$ analysis quantifies the pronounced separation between the non-CT and CT-based descriptions and thereby supports the onset of color transparency in the $ρ^0$ channel beyond what kinematic decay-length effects can accommodate.

hep-ph↗

arXiv2026

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 $α(Q^2)$ 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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arXiv2025

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

We investigate nuclear transparency induced by pion electroproduction on nuclei, $A(e,e'π^+)$, 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 $γ^*$ fluctuation into $ρ^0$, the two-step process with the $ρN$ scattering cross section chosen to be $σ_{ρN}=σ_{πN}$ 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 $A(e,e'π^+)$ reaction for $^{12}$C, $^{27}$Al, $^{63}$Cu, and $^{197}$Au nuclei. A discussion of the $Q^2$ dependence of the parameter $α$ for the transparency $T_A=A^{α-1}$ is given.

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arXiv2024

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

In the search for the pentaquark $Θ^+$ 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 $ρ^0(775)+ω(782)+ϕ(1020)$ vector meson exchange at high momenta. With the mass 1535 MeV and decay width 5 MeV the possibility of the $Θ^+$ 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 $Θ^+$ baryon among all spin and parity states $J^P = 1/2^\pm$ and $3/2^\pm$.

hep-ph↗

arXiv2023

Regge phenomenology of pion photoproduction off the nucleon at forward angles

We present a Regge model for pion photoproduction which is basically free of parameters within the framework of the s-channel helicity amplitude. We use coupling constants of all exchanged mesons determined from empirical decay widths or from the SU(3) relations together with consistency check with existing estimates that are widely accepted in other reaction processes. Cross sections and spin polarization asymmetries at various photon energies are analyzed and results are obtained in better agreement with experimental data without referring to any fitting procedure.

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arXiv2019

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

We investigate photoproduction of $ω$ off a nucleon target $γN\toωN$ by using a Reggeized model where $π(135)+σ(500)+f_1(1285)+f_2(1270)$+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 $π$ exchange with the absorptive cuts introduced to modulate the pion contribution to both $γp\to ωp$ and $γn\to ωn$ reactions. Necessity of $σ$ 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 $γp\to ωp$. Scaled differential cross sections of Jefferson Lab data on $γp\to ωp$ are investigated at the production angle $θ=90^\circ$ with the nonlinear trajectories for a saturation. Differential and total cross sections for the $γn\toωn$ reaction are analyzed to compare with recent experimental data at the CBELSA/TAPS Collaboration. An application to the $γp\toωΔ^+$ reaction is presented to demonstrate the significance of the $π$ exchange in the total and differential cross sections.

hep-ph↗

arXiv2016

Role of $ω$-meson exchange in scaling of the $γp\toπ^0 p$ process from a Regge-type model with resonances

The scaling of photoproduction $γp\toπ^0 p$ is investigated in the Reggeized model with $N^*$ and $Δ$ resonances included to describe resonance peaks up to photon energy $E_γ$= 3 GeV. Given the $t$-channel exchanges $ρ(770)+ω(780)+b_1(1235)+h_1(1170)$ Reggeized for the background contribution, the resonances of the Breit-Wigner form are introduced to agree with cross sections for total, differential and beam asymmetry in the low energy region. The scaled differential-cross sections $s^7{dσ/ dt}$ are reproduced to agree with the recent JLab data, revealing the production mechanism of the big bump structure around $W\approx 2.2$ GeV by the deep-dip pattern of the $ω$ exchange that originates from the zeros of the trajectory $α_ω(t)=0$ in the canonical phase, ${1\over2}(-1+e^{-iπα_ω(t)})$.

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arXiv2015

Pion and proton form factors in the Regge description of electroproduction $p(e,e'π^+)n$

Electroproduction of $π^+$ above the resonance region is analyzed in the Regge model for $π+ρ$ exchanges. Importance of the roles of pion and proton form factors in the process is discussed in comparison with existing models of Kaskulov and Mosel, and of Vrancx and Rychebusch. It is shown that the present model with proton form factor of a simple dipole-type yields a better description of DESY and JLab data over those models for high $Q^2$ and $-t$ region up to 5 GeV$^2$.

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arXiv2011

Evidence for the tensor meson exchange in the kaon photoproduction

The contribution of the tensor meson $K_2^*(1430)$ exchange in the process $γp\to K^+Λ(Σ^0)$ is investigated within the Regge framework. Inclusion of the $K_2^*$ exchange in the $K(494)+K^*(892)$ exchanges with the coupling constants chosen from the SU(3) symmetry leads to a better description of the production mechanism without referring to any fitting procedure. This shows the significance of the role of the tensor meson exchange to have the Regge theory basically free of parameters with the SU(3) symmetry a good approximation for the meson-baryon couplings.

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arXiv2009

Radiative decay of $K^-p$ system and photoproduction of $Λ(1405)$

The properties of the $Λ(1405)$ resonance have been investigated from radiative decay of $K^- p\to Yγ$ and photoproduction $γp\to K^+Λ(1405)$ within the framework of the isobar model. For a consistent result with recently measured branching ratios, the axial vector meson $K_1(1270)$ is taken into account. Strong and electromagnetic coupling constants of $Λ(1405)$ are extracted from these branching ratios and are applied to the analysis of $K^+Λ(1405)$ photoproduction. The total and differential cross sections are predicted.

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arXiv2005

Possibility of determinig the parity of the pentaquark $Θ^+$ from photoproduction near threshold

We discuss the possibility of determining the parity of the $Θ^+$ baryon from photoproduction $γN\to KΘ^+$ process near threshold. We utilize the conservation laws of parity and angular momentum for the analysis of angular distributions and spin observables near threshold. Since the discussion is in essence a partial wave analysis of the production mechanism the result should be less dependent on the model parameters. Our analysis shows that the angular distribution and photon polarization asymmetry for the process of neutron target are sensitive to the parity of the $Θ^+$, but not for the case of proton target. In the case of proton target, the polarization asymmetries of target and recoiled $Θ^+$ are preferred for parity determination.

nucl-th↗

arXiv2004

Investigating the parity of the exotic Theta^+ baryon from the kaon photoproduction

Based on the hadronic model with the gauge prescription suggested by Ohta and Haberzettl, we investigate the possibility of determining the parity state of the $Θ^+$ baryon using photon induced processes, $γn\to K^- Θ^+$ and $γp\to \bar{K}^0 Θ^+$. The total and differential cross sections are simulated in two versions of pseudovector(PV) and pseudoscalar(PS) coupling schemes and the results are reported both on the positive and negative parity states of the $Θ^+$ baryon. It is found that in both coupling schemes the total cross sections from the neutron target are in general larger than those from the proton target, regardless of the $Θ^+$ parities. The cross sections of the $Θ^+$ production however depend largely on the value of the $Θ^+$ decay width which is not yet well established. Moreover, there is a wide theoretical uncertainty associated with the different assumption on the gauge prescription in model calculations. We discuss these points by comparing theoretical predictions with the existing experimental data. Our analysis suggests that the observation of the angular distribution rather than just the total cross section in the photoproduction process may be a useful tool to distinguish the parity of the $Θ^+$ baryon.

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