Searcharxiv⌕ Search

arXiv subjects

Hyun-Chul Kim

Publications and source records attributed to Hyun-Chul Kim.

At least 109 records · Page 6Linked to original sources
arXiv2016

Heavy pentaquark states $P_c(4380)$ and $P_c(4450)$ in the $J/ψ$ production induced by pion beams off the nucleon

In this study, we investigate the $J/ψ$ production induced by pion beams off the nucleon, particularly the heavy pentaquarks $P_c(4380)$ and $P_c(4450)$ in intermediate states, based on a hybridized Regge model. The process involving $ρ$ and $π$ meson exchange in the $t$ channel is considered as background, and the heavy pentaquark exchange is included in the $s$ channel. The coupling constants such as the $ρNN$ and $πNN$ vertices are taken from the $NN$ potentials, whereas those for the $J/ψρπ$ and $J/ψππ$ vertices are determined by using experimental data based on the branching ratios. In order to estimate the $P_c(4380)$ and $P_c(4450)$ coupling constants, we use the experimental upper limit on the total cross section as a guide for the $πN\to J/ψN$ reaction. The background total cross section is the order of $10^{-4}-10^{-3}$ nb. In the vicinity of the heavy pentaquark masses, the total cross section reaches about $1$ nb.

hep-ph↗
arXiv2016

Pion mean fields and heavy baryons

We show that the masses of the lowest-lying heavy baryons can be very well described in a pion mean-field approach. We consider a heavy baryon as a system consisting of the $N_c-1$ light quarks that induce the pion mean field, and a heavy quark as a static color source under the influence of this mean field. In this approach we derive a number of \textit{model-independent} relations and calculate the heavy baryon masses using those of the lowest-lying light baryons as input. The results are in remarkable agreement with the experimental data. In addition, the mass of the $Ω_b^*$ baryon is predicted.

hep-ph↗
arXiv2016

$K^0 Λ$ and $D^- Λ_c^+$ production induced by pion beams off the nucleon

We present a comparative study of the pion induced production of $K^0 Λ$ and $D^- Λ_c^+$ off the nucleon. A hybrid framework is utilized by combining an effective Lagrangian method with a Regge approach. We consider the $t$-channel process in a plannar diagram by vector-meson Reggeon exchanges and the $u$-channel one in a non-planar diagram by baryon Reggeon exchanges. The present model reproduces the $K^0 Λ$ production data well with a few parameters. Having fixed them, we predict the $D^- Λ_c^+$ production, which turns out to be about $10^4-10^6$ times smaller than the strangeness one, depending on the kinematical regions.

hep-ph↗
arXiv2016

Bayesian Model Selection Methods for Mutual and Symmetric $k$-Nearest Neighbor Classification

The $k$-nearest neighbor classification method ($k$-NNC) is one of the simplest nonparametric classification methods. The mutual $k$-NN classification method (M$k$NNC) is a variant of $k$-NNC based on mutual neighborship. We propose another variant of $k$-NNC, the symmetric $k$-NN classification method (S$k$NNC) based on both mutual neighborship and one-sided neighborship. The performance of M$k$NNC and S$k$NNC depends on the parameter $k$ as the one of $k$-NNC does. We propose the ways how M$k$NN and S$k$NN classification can be performed based on Bayesian mutual and symmetric $k$-NN regression methods with the selection schemes for the parameter $k$. Bayesian mutual and symmetric $k$-NN regression methods are based on Gaussian process models, and it turns out that they can do M$k$NN and S$k$NN classification with new encodings of target values (class labels). The simulation results show that the proposed methods are better than or comparable to $k$-NNC, M$k$NNC and S$k$NNC with the parameter $k$ selected by the leave-one-out cross validation method not only for an artificial data set but also for real world data sets.

cs.LG↗
arXiv2016

Bayesian Kernel and Mutual $k$-Nearest Neighbor Regression

We propose Bayesian extensions of two nonparametric regression methods which are kernel and mutual $k$-nearest neighbor regression methods. Derived based on Gaussian process models for regression, the extensions provide distributions for target value estimates and the framework to select the hyperparameters. It is shown that both the proposed methods asymptotically converge to kernel and mutual $k$-nearest neighbor regression methods, respectively. The simulation results show that the proposed methods can select proper hyperparameters and are better than or comparable to the former methods for an artificial data set and a real world data set.

cs.LG↗
arXiv2016

Parity-violating $πNN$ coupling constant from the flavor-conserving effective weak chiral Lagrangian

We investigate the parity-violating pion-nucleon-nucleon coupling constant $h^1_{πNN}$, based on the chiral quark-soliton model. We employ an effective weak Hamiltonian that takes into account the next-to-leading order corrections from QCD to the weak interactions at the quark level. Using the gradient expansion, we derive the leading-order effective weak chiral Lagrangian with the low-energy constants determined. The effective weak chiral Lagrangian is incorporated in the chiral quark-soliton model to calculate the parity-violating $πNN$ constant $h^1_{πNN}$. We obtain a value of about $10^{-7}$ at the leading order. The corrections from the next-to-leading order reduce the leading order result by about 20~\%.

hep-ph↗
arXiv2016

Charmed baryons and their interactions

In this proceedings report, we discuss unique features of charmed, or in general heavy, baryons with one heavy quark. A well and long-term known phenomena, the distinction of the two modes of the rho and lambda type of a three-quark system is revisited. The difference of these modes may be tested in the production and decay reactions of the baryons which may be tested in the future experiments at J-PARC.

hep-ph↗
arXiv2015

Modification of generalized vector form factors and transverse charge densities of the nucleon in nuclear matter

We investigate the medium modification of the generalized vector form factors of the nucleon, which include the electromagnetic and energy-momentum tensor form factors, based on an in-medium modified $π$-$ρ$-$ω$ soliton model. We find that the vector form factors of the nucleon in nuclear matter fall off faster than those in free space, which implies that the charge radii of the nucleon become larger in nuclear medium than in free space. We also compute the corresponding transverse charge densities of the nucleon in nuclear matter, which clearly reveal the increasing of the nucleon size in nuclear medium.

hep-ph↗
arXiv2015

Production of strange and charmed baryons in pion induced reactions

We study the strangeness and charm productions induced by the pion beam, i.e. the $π^-$p $\rightarrow$ $K^{*0}Λ$ and $π^-$p $\rightarrow$ $D^{*-}Λ_c^+$ reactions, based on two different theoretical frameworks: an effective Lagrangian method and a Regge approach. In order to estimate the magnitude of the charm production relative to that of the strangeness production, we assume that the coupling constants for the charmed meson and baryon vertices are the same as those for the strangeness channel. We found that the total cross section for the charm production was about $10^3 - 10^6$ times smaller than that for the strangeness production, depending on theoretical approaches and kinematical regions. We also discuss each contribution to observables for both reactions. In general, the Regge approach explains the experimental data very well over the whole energy region.

hep-ph↗
arXiv2015

Pion Induced Reactions for the Study of Charmed Baryons

In this talk, we report the study of $π^- p \to K^{*0} Λ$ and $π^- p \to D^{*-} Λ_c^+$ reactions by using an effective Lagrangian method and a hybrid Regge model. The total and differential cross sections for the $K^{*0} Λ$ production are first calculated and then those for the $D^{*-} Λ_c^+$ one are estimated. The two models yield different results, each exhibiting specific features. Our prediction for the charm production provides valuable information about the upcoming J-PARC experiment.

hep-ph↗
arXiv2015

Photoproduction of the Scalar Meson $f_0(500)$

In the present talk, we report a recent investigation on photoproduction of the $γN \to f_0(500)N$ within a framework of the effective Lagrangian. We include the nucleon resonances with pin $1/2$ in the $s$ channel. The coupling constants have been etermined by assuming that the decay process $N^* \to (ππ)_{I=0,J=0}N$ can be regarded as $N^* \to f_0(500) N$. We discuss the numerical results for the total cross sections and possible extension of the present work.

hep-ph↗
arXiv2015

Weak $K\to π$ generalized form factors and transverse transition quark-spin density from the instanton vacuum

We investigate the generalized $K\to π$ transition vector and tensor form factors, from which we derive the transverse quark spin density in the course of the $K\toπ$ transition, based on the nonlocal chiral quark model from the instanton vacuum. The results of the transition tensor form factor are in good agreement with recent data of lattice QCD. The behavior of the transverse quark spin density of the $K\toπ$ transition turn out to be very similar to those of the pion and the kaon.

hep-ph↗
arXiv2015

Hyperon Semileptonic decay constants with flavor SU(3) symmetry breaking

We investigate the hyperon semileptonic decay constants, $f_2/f_1$, and $g_1/f_1$, within a general framework of a chiral soliton model. All relevant parameters for the SU(3) baryon wave functions were unambiguously determined by using the experimental data for the masses of the baryon octet and the decuplet. Using then the existing experimental data for the magnetic moments of the baryon octet and the decay constants of hyperon semileptonic decays, we are able to determine all the hyperon semileptonic decay constants $f_2/f_1$ and $g_1/f_1$ of the baryon octet unequivocally. In addition, we also present the results of the axial-vector transition constants from the baryon decuplet to the octet.

hep-ph↗
arXiv2014

Stability of the pion and the pattern of chiral symmetry breaking

We investigate the pressure of the pion, which should be equal to zero to ensure the stability of the pion, within the framework of the chiral quark model beyond the chiral limit. The pressure of the pion turns out to vanish nontrivially by the Gell-Mann-Oakes-Renner relation within the present framework. It implies that the stability of the pion might be deeply rooted in spontaneous chiral symmetry breaking. We also discuss physical quantities relevant to the energy-momentum tensor operator.

hep-ph↗
arXiv2014

Effects of $N(2000)\, 5/2^+$, $N(2060)\,5/2^-$, $N(2120)\,3/2^-$, and $N(2190)\,7/2^-$ on $K^*Λ$ photoproduction

We reinvestigate $K^*Λ(1116)$ photoproduction off the nucleon target, based on an effective Lagrangian approach. We include higher nucleon resonances such as $N(2000)\, 5/2^+$, $N(2060)\,5/2^-$, $N(2120)\,3/2^-$, and $N(2190)\,7/2^-$, of which the data are taken from the 2012 edition of Review of Paritcle Physics, in addition to the $t$-channel diagrams ($K$, $K^*$, and $κ$), the $s$-channel nucleon, and $u$-channel hyperon($Λ$, $Σ$, and $Σ^*$) contributions. We find that the $N(2120)\,3/2^-$ and $N(2190)\,7/2^-$ resonances are essential in describing the new CLAS data for charged $K^*$ photoproduction. On the other hand, they rarely affect for neutral $K^*$ photoproduction.

hep-ph↗
arXiv2014

Pion induced Reactions for Charmed Baryons

We study pion induced reactions for charmed baryons $B$, $π$ + N $\rightarrow$ $D^*$ + $B$. First we estimate charm production rates in comparison with strangeness production using a Regge model which is dominated by vector ($D^*$ or $K^*$ ) Reggeon exchange. Then we examine the production rates of various charmed baryons $B$ in a quark-diquark model. We find that the production of excited states are not necessarily suppressed, a sharp contrast to strangeness production, which is a unique feature of the charm production with a large momentum transfer.

hep-ph↗
arXiv2014

Energy-momentum tensor form factors of the nucleon within a $π$-$ρ$-$ω$ soliton model

We investigate the energy-momentum tensor form factors of the nucleon within the famework of a chiral soliton model, including the $ρ$ and $ω$ vector mesons. We examine the role of each meson degrees of freedom in these form factors. It is explicitly shown that the pion provides strong attraction whereas the $ρ$ and $ω$ yield repulsion in such a way that the soliton becomes stabilized. The results are discussed in comparison with those of other models.

hep-ph↗