arXiv subjects

Yongseok Oh

Publications and source records attributed to Yongseok Oh.

At least 91 records · Page 5Linked to original sources

arXiv2005

Photo-excitation of hyperons and exotic baryon in gamma N --> K Anti-K N

We investigate the reaction of $γN \to K \bar{K} N$ focusing on the photoproduction of $Λ(1520)$ and putative exotic $Θ(1540)$. We consider various background production mechanisms including the production of vector mesons, tensor mesons, and other $Λ$ and $Σ$ hyperons. We discuss the angular distribution of $Λ(1520)$ photoproduction cross section and the radiative decays of $Λ(1520)$. We also discuss what we expect for the invariant mass distributions if the $Θ(1540)$ is formed in the reaction, with the parameters studied so far. We find that the peak in the $KN$ invariant mass distribution, if confirmed, can hardly come from the kinematic reflections, especially, due to the tensor meson backgrounds.

hep-ph↗

arXiv2005

Pentaquark Theta^+(1540) production in gamma N --> K Anti-K N

The recent developments in the search of exotic pentaquark hadrons are briefly reviewed. We then focus on investigating how the exotic pentaquark $Θ(1540)$ baryon production can be identified in the $γN \to K \bar{K} N$ reactions, focusing on the influence of the background (non-$Θ$ production) mechanisms. By imposing the SU(3) symmetry and using various quark model predictions, we are able to fix the coupling constants for evaluating the kaon backgrounds, the $K\bar{K}$ production through the intermediate vector meson and tensor meson photoproduction, and the mechanisms involving intermediate $Λ(1116)$, $Λ(1405)$, $Λ(1520)$, $Σ(1193)$, $Σ(1385)$, and $Δ(1232)$ states. The total cross section data of $γp \to K^+K^- p$ is then used to fix the form factors which regularize the background amplitudes so that the signal of $Θ(1540)$ in $γn \to K^+K^-n$ and $γp \to K^0\bar{K}^0p$ cross sections can be predicted. We find that the predicted $K^+K^-$ and $K^+ n$ invariant mass distributions of the $γn \to K^+ K^- n$ reaction can qualitatively reproduce the shapes of the JLab data. However, the predicted $Θ(1540)$ peak can not be identified unambiguously with the data. High statistics experiments are needed to resolve the problem. We also find that an even-parity $Θ$ is more likely to be detected, while it will be difficult to identify an odd-parity $Θ$, even if it exists, from the background continuum, if its coupling constants are small as in the present quark model predictions.

hep-ph↗

arXiv2005

D_s (2317) as a four-quark state in QCD sum rules

We perform a QCD sum rule study of the open-charmed $D_s (2317)$ as a four-quark state. Using the diquark-antidiquark picture for the four-quark state, we consider four possible interpolating fields for $D_s (2317)$, namely, scalar-scalar, pseudoscalar-pseudoscalar, vector-vector, and axial-vector--axial-vector types. We test all four currents by constructing four separate sum rules. The sum rule with the scalar-scalar current gives a stable value for the $D_s$ mass which qualitatively agrees with the experimental value, and the result is not sensitive to the continuum threshold. The vector-vector sum rule also gives a stable result with small sensitivity to the continuum threshold and the extracted mass is somewhat lower than the scalar-scalar current value. On the other hand, the two sum rules in the pseudoscalar and axial-vector channels are found to yield the mass highly sensitive to the continuum threshold, which implies that a four-quark state with the combination of pseudoscalar-pseudoscalar or axial-vector--axial-vector type would be disfavored. These results would indicate that $D_s (2317)$ is a bound state of scalar-diquark and scalar-antidiquark and/or vector-diquark and vector-antidiquark.

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arXiv2005

Pentaquarks in SU(3) quark model

Based on the flavor SU(3) symmetry, we classify all the possible pentaquark baryons made of four quarks and one antiquark. In particular, we present possible multiplets of pentaquarks, their interactions with mesons, and the mass relations within a multiplet. We also study the pentaquark decays in the generalized OZI rule.

hep-ph↗

arXiv2005

Decay modes of ideally mixed narrow pentaquark states

We investigate the decay modes of pentaquark baryons for both the antidecuplet and the octet states, which were recently claimed by Close and Dudek to be potentially narrow due to a hidden selection rule. We discuss how ideal mixing between the pentaquark octet and antidecuplet states can be related to the OZI rule, which also naturally leads to certain selection rules in the pentaquark decays. We then introduce a tensor representation for the pentaquark states, and present the possible decay modes for both the unmixed and ideally mixed pentaquark octet and antidecuplet states. The exclusive decay modes can be used to experimentally search for the other pentaquark states.

hep-ph↗

arXiv2004

Flavor structure of pentaquark baryons in quark model

The flavor SU(3) group structure of pentaquark baryons which form $\bm{1}$, $\bm{8}$, $\bm{10}$, $\bar{\bm{10}}$, $\bm{27}$, and $\bm{35}$ multiplets is investigated in quark model. The flavor wave functions of all the pentaquark baryons are constructed in SU(3) quark model and their Yukawa interactions with meson octet are obtained in general and in the special case of the octet-antidecuplet ideal mixing with the OZI rule. The mass sum rules of pentaquark baryons are also discussed.

hep-ph↗

arXiv2004

Spin asymmetries in gamma + N --> K*bar + Theta^+

The photoproduction processes of the exotic $Θ^+(1540)$ baryon and the $\bar{K}^*$ meson from the nucleon targets, i.e., $γn \to K^{*-} Θ^+$ and $γp \to \bar{K}^{*0} Θ^+$, are investigated in a hadronic model. We consider $K$ and $K^*$ exchanges as well as the $s$ and $u$ channel nucleon and $Θ$ terms. Various spin asymmetries together with cross sections are first computed in order to study the production mechanisms and the parity of the $Θ^+(1540)$ baryon. Within the uncertainties arising from the model-dependence of the production mechanisms and several coupling constants, we find that some target-recoil double spin asymmetries, $C^{\rm TR}_{xx'}$ and $C^{\rm TR}_{xz'}$, are sensitive to the parity of $Θ^+$. In addition, the parity asymmetry of this reaction on the neutron target, which can be obtained by analyzing $K^*$ decay distribution, is found to be useful to estimate the $K^* N Θ$ coupling.

hep-ph↗

arXiv2004

Pentaquark baryons in SU(3) quark model

We study the SU(3) group structure of pentaquark baryons which are made of four quarks and one antiquark. The pentaquark baryons form {1}, {8}, {10}, {10}-bar, {27}, and {35} multiplets in SU(3) quark model. First, the flavor wave functions of all the pentaquark baryons are constructed in SU(3) quark model and then the flavor SU(3) symmetry relations for the interactions of the pentaquarks with three-quark baryons and pentaquark baryons are obtained.

hep-ph↗

arXiv2004

Anti-charmed pentaquark $Θ_c (3099)$ from QCD sum rules

We construct QCD sum rules for the anti-charmed pentaquark $Θ_c (3099)$, recently reported at HERA. The sum rules are constructed similarly with the $Θ^+ (1540)$ sum rules using the anti-charmed analogue of the $Θ^+$ interpolating field. The strange quark and quark-gluon mixed condensates, which were important in the $Θ^+$ sum rules, are replaced by the gluon condensates whose contribution to the OPE is suppressed due to the heavy quark mass. Our result suggests that the parity of $Θ_c$ is positive. We identify the difference from the $Θ^+$ sum rule, which leads to the positive parity in this heavy-light pentaquark system. The obtained mass is similar to the experimental value.

hep-ph↗

arXiv2004

Properties of baryon anti-decuplet

We study the group structure of baryon anti-decuplet containing the $Θ^+$. We derive the SU(3) mass relations among the pentaquark baryons in the anti-decuplet, when there is either no mixing or ideal mixing with the pentaquark octet, as advocated by Jaffe and Wilczek. This constitutes the Gell-Mann--Okubo mass formula for the pentaquark baryons. We also derive SU(3) symmetric Lagrangian for the interactions of the baryons in the anti-decuplet with the meson octet and the baryon octet. Our analysis for the decay widths of the anti-decuplet states suggests that the N(1710) is ruled out as a pure anti-decuplet state, but it may have anti-decuplet component in its wavefunction if the multiplet is mixed with the pentaquark octet.

hep-ph↗

arXiv2003

Theta^+ baryon production in KN and NN reactions

We study $Θ^+(1540)$ productions in kaon-nucleon ($KN$) and nucleon-nucleon ($NN$) interactions by assuming that the $Θ^+$ is an isosinglet with $J^P = \frac12^+$. Possible $t$-channel diagrams with $K^*$ exchange are considered in both reactions as well as $K$ exchange in $NN$ reaction. The cross section for $np \to Λ^0 Θ^+$, which has not been considered in previous calculations, is found to be about a factor of 5 larger than that for $np \to Σ^0 Θ^+$ due to the large coupling of $KNΛ$ interaction. The cross sections are obtained by setting $g_{KNΘ}^{}=1$ and varying the ratio of $g_{K^*NΘ}^{}/g_{KNΘ}^{}$ so that future experimental data can be used to estimate these couplings. We also find that the isospin relations hold for these reactions.

hep-ph↗

arXiv2003

Exotic Theta^+ baryon production induced by a photon and a pion

We investigate the photoproduction of the $Θ^+(1540)$ on a nucleon ($γn \to K^- Θ^+$, $γp \to \bar{K}^0 Θ^+$) and the pion-induced $Θ^+$ production reaction on the proton ($π^- p \to K^- Θ^+$). The total cross sections near threshold are estimated by using hadronic models with effective interaction Lagrangians and form factors that preserve gauge-invariance of the electromagnetic current. The photoproduction cross sections are found to be a few hundred nb, with the cross section on the proton being larger than that on the neutron. The pion-induced production cross section is found to be around a few hundred $μ$b but sensitive to the $K^* N Θ$ coupling whose value is not yet known. We also study the production cross section assuming that the $Θ^+$ has negative parity. The cross sections are then found to be much suppressed compared to the case where $Θ^+$ has positive parity. Hence, the interpretation of the $Θ^+$ as an odd-parity pentaquark state seems to be disfavored from the estimates of cross section for the photon-proton reaction from the SAPHIR experiment.

hep-ph↗

arXiv2003

Rho meson photoproduction at low energies

The $σ$-exchange and $f_2$-exchange mechanisms for $ρ$ meson photoproduction are re-examined. Then the commonly employed $σ$-exchange amplitude is revised by using the recent information from the analyses on the $ρ\to π^0π^0γ$ decay and the $σNN$ coupling constant from Bonn potential. Instead of relying on the Pomeron-$f$ proportionality assumption, the $f_2$ meson exchange amplitude is established from an effective Lagrangian which is constructed from the tensor structure of the $f_2$ meson. Phenomenological information together with tensor meson dominance and vector meson dominance assumptions are used to estimate the $f_2$ coupling constants. As a first step to improve the current theoretical models, we have also explored the effects due to the un-correlated $2π$ exchange amplitude with $πN$ intermediate state. This leading-order $2π$ exchange amplitude can be calculated using the coupling constants determined from the study of pion photoproduction and the empirical width of $ρ\to ππ$ decay. In comparing with the existing differential cross section data, we find that a model with the constructed $2π$, $σ$, and $f_2$ exchanges is comparable to the commonly used $σ$ exchange model in which the $σ$ coupling parameters are simply adjusted to fit the experimental data. We suggest that experimental verifications of the predicted single and double spin asymmetries in the small $|t|$ ($ < 2$ GeV$^2$) region will be useful for distinguishing the two models and improving our understanding of the non-resonant amplitude of $ρ$ photoproduction. Possible further improvements of the model are discussed.

nucl-th↗

arXiv2003

Higher meson resonances in $ρ\to π^0 π^0 γ$ and $ω\to π^0 π^0 γ$

The role of higher meson resonances with spin 1 and 2 is investigated quantitatively in the decay processes of $ρ\to π^0π^0 γ$ and $ω\to π^0 π^0 γ$. Among the higher resonances, we find that the $f_2(1270)$ tensor meson can give a nontrivial contribution especially to the $ω\to π^0 π^0 γ$ decay process. When the $f_2$ contribution is combined with the processes involving the vector and scalar meson intermediate states, a good agreement with the recent measurements is achieved for both decays. The effect of the $f_2(1270)$ is found to be sizable at the intermediate photon energies and may be verified by precise measurements of the recoil photon spectrum of the $ω\to π^0 π^0 γ$ decay. The dependence of the decay widths on various models for the $ρ$-$ω$ mixing in the literature is also investigated.

hep-ph↗

arXiv2003

f_2, sigma, and 2-pi exchanges in rho meson photoproduction

The $σ$ meson exchange model for $ρ$ photoproduction at low energies is re-examined and a new model is developed by considering explicit two-pion exchange and the $f_2$ tensor meson exchange. The $f_2$ exchange model, which is motivated by the low energy proton-proton elastic scattering, is constructed by fully taking into account of the tensor structure of the $f_2$ meson interactions. Phenomenological informations together with tensor meson dominance and vector meson dominance assumptions are used to estimate the $f_2$ meson's coupling constants. For $2π$ exchange, the loop terms including intermediate $πN$ and $ωN$ channels are calculated using the coupling constants determined from the study of pion photoproduction. It is found that our model with $f_2$ and $2π$ exchanges can successfully replace the commonly used $σ$ exchange model that suffers from the big uncertainty of the coupling constants. We found that the two models can be distinguished by examining the single and double spin asymmetries.

nucl-th↗

arXiv2003

Vector meson photoproduction processes near threshold

We discuss the photoproduction processes of light vector mesons ($ρ$, $ω$, and $ϕ$) from the nucleon near threshold. We first develop a simple model based on meson exchanges which is modified by the nucleon pole terms. We then extend this model to study other physically interesting topics. As examples, we discuss the missing nucleon resonances problem in $ω$ photoproduction and the direct $ϕNN$ coupling constant in $ϕ$ photoproduction. The calculated cross sections are compared with the recent experimental data. Various spin observables are discussed, which may be measured at current photon/electron facilities such as TJNAF and SPring-8 of RCNP. Precise measurements of such quantities would provide very useful information to understand the production mechanism.

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arXiv2002

pi and rho loop corrections to omega photoproduction in the resonance region

One-loop corrections due to the intermediate $πN$ and $ρN$ states are studied in $ω$ photoproduction near threshold. Our results show that the coupled-channel effects should be taken into account in extracting reliable nucleon resonance parameters from the forthcoming vector meson photoproduction data in the resonance region.

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arXiv2002

One-loop corrections to omega photoproduction near threshold

One-loop corrections to $ω$ photoproduction near threshold have been investigated by using the approximation that all relevant transition amplitudes are calculated from the tree diagrams of effective Lagrangians. With the parameters constrained by the data of $γN \to πN$, $γN \to ρN$, and $πN \to ωN$ reactions, it is found that the one-loop effects due to the intermediate $πN$ and $ρN$ states can significantly change the differential cross sections and spin observables. The results from this exploratory investigation suggest strongly that the coupled-channel effects should be taken into account in extracting reliable resonance parameters from the data of vector meson photoproduction in the resonance region.

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