arXiv subjects

Byung-Geel Yu

Publications and source records attributed to Byung-Geel Yu.

28 records · Page 2Linked to original sources

arXiv2017

Nondiffractive feature of $γN\to ρ^\pm N$ with $ρ$-meson electromagnetic multipole moments

We investigate photoproduction of charged $ρ$ off the nucleon using $ρ(770)+π(140)$ Regge pole exchanges by considering the $ρ$-meson electromagnetic multipole moments. The significance of the Ward identity at the $γρρ$ vertex is emphasized for current conservation in the process. Given $π$ exchange with the well-known coupling constants for $γπρ$ and $πNN$, we analyze the role of the $ρ$ exchange in the $γp\to ρ^+n$ and $γn\toρ^-p$ processes without model-dependences except for the magnetic moment $μ_{ρ^\pm}=\pm2.01$ and electric quadrupole moment ${\cal Q}_{ρ^\pm}=\pm0.027$ fm$^2$ taken from theoretical estimates. The nondiffractive feature of both cross sections is reproduced with a rapid decrease beyond the resonance region by the dominance of $π$ exchange over the $ρ$\,. % Cross sections for differential and density matrix elements are presented to compare with existing data. The parity and photon polarization asymmetries are predicted to demonstrate the apparent roles of the $ρ$-meson electromagnetic multipole moments.

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arXiv2017

Role of $σ$ exchange in the $γp\to ϕp$ process and scaling with the $f_1$ axial vector meson from a Reggeized model

We investigate the role driven by the scalar meson $σ$ exchange in the photoproduction of the vector meson $ϕ$(1020) off a proton by using a Reggeized model. Based on the $π^0(135)+σ(500)+f_2(1270)$+Pomeron exchanges, we demonstrate that the $σ$ 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 $s^7dσ/dt$ at the production angle $θ=90^{\circ}$ from the CLAS data. It is found that the axial vector meson $f_1(1285)$ exchange with the trajectory $α_{f_1}(t)=0.028\,t+0.9\pm0.2$ arising from the axial anomaly of the QCD vacuum plays the role to clarify the scaling up to 5 GeV.

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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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arXiv2016

Regge approach to the reaction of $γN \to K^* Λ$

Photoproduction of $K^*$ vector mesons off nucleon is investigated within the Regge framework where the electromagnetic vertex of $γK^*K^*$ fully takes into account the magnetic dipole and electric quadrupole moments of spin-1 $K^*$ vector meson. The $t$-channel $K^*(892)$, $K(494)$ and $κ(800)$ meson exchanges are considered for the analysis of the production mechanism. The experimentally observed rapid decrease of the cross sections for the $γp \to K^{*+} Λ$ reaction beyond the resonance region is well reproduced by the dominance of the exchange of $K$-meson trajectory. The role of the scalar $κ$-meson trajectory is found to be minor in both $γp$ and $γn$ reactions. The cross sections for the $γn \to K^{*0} Λ$ reaction are predicted to be about twice those of the $γp \to K^{*+}Λ$ reaction. The role of the $K^*$ electromagnetic multipoles and the proton anomalous magnetic moment is studied through the total and differential cross sections and spin/parity asymmetries. We suggest the measurement of the photon polarization asymmetry as a tool for identifying the role of the magnetic dipole and electric quadrupole moments of the $K^*$ vector meson.

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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.

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arXiv2012

Photoproduction of K* meson off the proton target with the Regge contributions

We investigate the K* Lambda(1116) photoproduction off the proton target, employing the tree-level Born approximation within the effective Lagrangian approach. We take into account the kappa, K, and K* exchanges in the t channel in addition to the ground-state nucleon- and hyperon-pole contributions in the s and u channels with the gauge-invariant form-factor scheme. The nucleon and hyperon resonances, D_13(2080) and Sigma*(1385) are also included. We take into account the Regge trajectories of the strange-mesons for the t-channel contributions in such a way that the Feynman and Regge propagators are interpolated smoothly for the relevant photon energy region. We provide numerical results for the differential cross sections, which result in qualitatively good agreement with the presently available experimental data from CLAS collaboration at Jefferson laboratory. It turns out that the Feynman-Regge interpolation for the meson exchanges play a critical role in reproducing the data simultaneously for the low and relatively high energy regions. We also compute the total cross sections, momentum-transfer dependence of the differential cross sections in the t-channel, and the photon-beam asymmetry as useful guides for future experiments.

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arXiv2011

Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model

In this talk we present our recent studies for the unpolarized fragmentation functions for the pion and kaon, employing the nonlocal chiral quark model, which manifests the nonlocal interaction between the quarks and pseudoscalar mesons, in the light-cone frame. It turns out that the nonlocal interaction produces considerable differences in comparison to typical local-interaction models.

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arXiv2011

Charged pion photoproduction with the Delta(1232) baryon beyond the resonance region

We investigate the charged pion photoproduction off the proton target with the Delta(1232) baryon in the final state, i.e. gamma p -> pi^- Delta^++(1232) and gamma p -> pi^+ Delta^0(1232), based on the effective Lagrangian method, beyond the resonance region, E_cm >~ GeV. We employ the pi- and rho-meson Regge trajectories in the t-channel, in addition to the proton- and Delta-pole, in the s- and u-channels respectively, and the contact-interaction contributions. A specific scheme for the form factor which satisfies the Ward-Takahashi identity, crossing symmetry, and on-shell condition, is taken into account. To discuss the validity of the Regge approach within the Effective Lagrangian method, we also consider a smooth interpolation between the Regge- and Feynman-propagators for the t-channel meson exchanges as a function of sqrt(s). We present the numerical results for the energy and angular dependences of the cross sections, and double-polarization observable. It turns out that the present framework shows the significance of the pi-exchange and contact interaction terms to reproduce the experimental data qualitatively well. Especially, the interpolation between the two propagators plays a crucial role to reproduce the high-energy experimental data. The pi^+ decay-angle distribution is also studied using the Delta^++ decay frame, i.e. the Gottfried-Jackson frame. The present results will be a useful guide for future high-energy photon-beam experiments.

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arXiv2011

Lambda(1520) photoprodcution with Regge contribution

In this talk, we report our recent progresses on the Lambda(1520) photoproduction using the effective Lagrangian approach. In addition to the tree-level Born diagrams, we take into account the Regge-trajectories for the possible strange-meson exchanges in the t channel. We compute the angular and energy dependences of the production process, including polarization observables, such as the photon-beam asymmetry and the polarization-transfer coefficients, resulting in good qualitative agreement with current experimental data. We also compute the K^- angle distribution function in the Gottfried-Jackson frame, using the polarization-transfer coefficients in the z direction.

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arXiv2010

QCD under magnetic field: chiral magnetic effect at heavy ion collisions

In this talk, we report our recent studies for the chiral magnetic effect, which signals the P- and CP-violations at the heavy ion collisions. We compute the electric current and its correlations, induced by the external magnetic field, inside the hot and dense QCD matter created in the heavy ion collisions. For this purpose, we employ the instanton-liquid model, modified by the Harrington-Shepard caloron at finite T. We observe that the chiral magnetic effect current and its correlations increase with respect to the magnetic field, whereas they decrease as functions of T, due to the diluting instanton ensemble. It turns out that the numerical results are in good agreement with those from the model-independent analyses and lattice QCD simulations. We also reproduce the charge separations, observed in the STAR experiment, qualitatively well, considering the simplified Lienard-Wiechert potential, screening and size effects.

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