arXiv subjects

Myung Ki Cheoun

Publications and source records attributed to Myung Ki Cheoun.

11 recordsLinked to original sources

arXiv2007

Strange quark contributions to neutrino and antineutrino nucleus scattering via neutral current in quasi-elastic region

Strange quark contributions to the neutral current reaction in the neutrino scattering are investigated on the nucleon level and extended to the $^{12}$C target nucleus through the neutrino-induced knocked-out nucleon process in the quasi-elastic region within the framework of a relativistic single particle model. The incident energy range between 500 MeV and 1.0 GeV is used for the neutrino(antineutrino) scattering. Effects of the final state interaction for the knocked-out nucleon are included by a relativistic optical potential. We found that the sensitivity of the strange quark contents could be salient on the asymmetry between neutrino and antineutrino scattering cross sections. In specific, $A (ν({\bar ν}), ν^{'} ({\bar ν}^{'}) N)$ reaction is shown to be very sensitive test in the searches of the strangeness.

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arXiv2006

The pseudo scalar form factor of the nucleon, the sigma-like term, and the $L_0^+$ amplitude for charged pion electro-production near threshold

The pseudo scalar form factor, which represents the pseudo scalar quark density distribution due to finite quark masses on the nucleon, is shown to manifest itself with the induced pseudo scalar form factor in the $L_0^+$ amplitude for the charged pion electro-production. Both form factors show their own peculiar momentum dependence. Under the approximation on which the Goldberg-Treimann relation holds, a sum of both form factors' contributions accounts for the t-channel contribution in the charged pion electro-production near threshold.

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arXiv2001

A Role of the Axial Vector Mesons on the Photon Production in Heavy Ion Collisions and Their Relevant Decays

A role of the axial vector mesons, such as $K_1$ and $a_1$, on the emitted photon spectrum in hot hadronic matter is studied through the channels $πρ\to a_1 \to πγ$ and $K ρ\to K_1 \to K γ$. They are shown to be dominant channels in this spectrum. This study is carried out with an effective chiral lagrangian which includes vector and axial-vector mesons and explains well their relevant decays simultaneously.

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arXiv2000

Pion and Kaon Electromagnetic Form Factors in a $SU_{L}(3)\otimes SU_{R}(3)$ Effective Lagrangian

A SU(2) effective lagrangian is extended to a $SU_{L}(3)\otimes SU_{R}(3)$ by including the vector and axial vector meson. With this effective lagrangian, electromagnetic form factors of charged pion and kaon are calculated. The pseudoscalar meson loops are taken into account. Good agreement with experimental data is obtained for those form factors. Decay widths of $ρ\to ππ$ and $ϕ\to K^{+}K^{-}$ are also calculated and shown to agree with experimental data very well.

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arXiv1999

An Isobaric Model for Kaon photoproduction

The kaon photoproduction is analyzed up to $E_γ^{\rm Lab}$=2.0 GeV by using an isobaric model based on effective Lagrangians and by taking a cross symmetry into account. Both {\it pseudovector} and {\it pseudoscalar} couplings for kaon-baryon-baryon (baryon spin=1/2) interactions are considered with form factors. A vector meson($K^*(890)$), an axial vector meson($K_1(1270)$), nucleon resonances($J\le5/2$), and hyperon resonances($J\le3/2$) are treated as participating particles. By determining unknown coupling constants through a systematic fitting of the differential cross section, the total cross section, the single polarization observable, and the radiative kaon capture branching ratio to their experimental data, we find out a simple model which reproduces all the experimental data well.

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arXiv1999

Importance of the Doppler Effect to the Determination of the Deuteron Binding Energy

The deuteron binding energy extracted from the reaction ${}^1H(n,γ){}^2H$ is reviewed with the exact relativistic formula, where the initial kinetic energy and the Doppler effect are taken into account. We find that the negligible initial kinetic energy of the neutron could cause a significant uncertainty which is beyond the errors available up to now. Therefore, we suggest an experiment which should include the detailed informations about the initial kinetic energy and the detection angle. It could reduce discrepancies among the recently reported values about the deuteron binding energy and pin down the uncertainty due to the Doppler broadening of $γ$ ray.

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arXiv1998

Induced Pseudoscalar Coupling Constant

The recent TRIUMF experiment for $μ^- p \to n ν_μ γ$ gave a surprising result that the induced pseudoscalar coupling constant $g_P$ was larger than the value obtained from $μ^- p \to n ν_μ$ experiment as much as 44 %. Reexamining contribution of the axial vector current, we found an additional term to the matrix element of Beder and Fearing which was used to extract the $g_P$ value from the measured photon energy spectrum. This additional term plays a key role to restore the reliability of $g_P (- 0.88 m_μ^2) = 6.77 g_A (0)$.

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arXiv1998

Radiative Muon Capture and Induced Pseudoscalar Coupling Constant in Nuclear Matter

The recent TRIUMF experiment for $μ^- p \to n ν_μ γ$ gave a surprising result that the induced pseudoscalar coupling constant $g_P$ was larger than the value obtained from $μ^- p \to n ν_μ$ experiment as much as 44 %. Reexamining contribution of the axial vector current in electromagnetic interaction, we found an additional term to the matrix element which was used to extract the $g_P$ value from the measured photon energy spectrum. This additional term, which plays a key role to restore the reliability of $g_P (- 0.88 m_μ^2) = 6.77 g_A (0)$, is shown to affect the $g_P$ quenching problems in nucleus.

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arXiv1998

The Axial Current in Electromagnetic Interaction

We discussed the possibility that the charged axial currents of matter fields could be non-conserved in electromagnetic interaction at $O(e) $ order. It means that chiral symmetry is broken explicitly by electromagnetic interaction. This explicit symmetry breaking of chiral symmetry is shown to lead the mass differences between the charged and neutral particles of matter fields.

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arXiv1997

$Σ$ Like Term in Pion Electroproduction Near Threshold

Sum of the time component of $Σ$ term and the induced pseudo scalar term in axial current is shown to be the t-channel pion pole in Born terms for pion electroproduction near threshold. We also show that this $Σ$ term represents the charged pseudo scalar quark density matrix elements in nucleon and manifests itself in the $L_0^+$ amplitude on this reaction.

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arXiv1995

$g_{K N Λ}$ and $g_{K N Σ}$ from QCD sum rules

$g_{K N Λ}$ and $g_{K N Σ}$ are calculated using a QCD sum rule motivated method used by Reinders, Rubinstein and Yazaki to extract Hadron couplings to goldstone bosons. The SU(3) symmetry breaking effects are taken into account by including the contributions from the strange quark mass and assuming different values for the strange and the up down quark condensates. We find $g_{K N Λ}/\sqrt{4 π} = - 1.96 $ and $g_{K N Σ}/\sqrt{4 π} = 0.33 $

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