arXiv subjects

Hungchong Kim

Publications and source records attributed to Hungchong Kim.

At least 37 records · Page 2Linked to original sources

arXiv2005

QCD sum rules for the anti-charmed pentaquark

We present a QCD sum rule analysis for the anti-charmed pentaquark state with and without strangeness. While the sum rules for most of the currents are either non-convergent or dominated by the $DN$ continuum, the one for the non-strange pentaquark current composed of two diquarks and an antiquark, is convergent and has a structure consistent with a positive parity pentaquark state after subtracting out the $DN$ continuum contribution. Arguments are presented on the similarity between the result of the present analysis and that based on the constituent quark models, which predict a more stable pentaquark states when the antiquark is heavy.

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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.

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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.

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arXiv2005

Parity of $Θ^+$(1540) from QCD sum rules

The QCD sum rule for the pentaquark $Θ^+$, first analyzed by Sugiyama, Doi and Oka, is reanalyzed with a phenomenological side that explicitly includes the contribution from the two-particle reducible kaon-nucleon intermediate state. The magnitude for the overlap of the $Θ^+$ interpolating current with the kaon-nucleon state is obtained by using soft-kaon theorem and a separate sum rule for the ground state nucleon with the pentaquark nucleon interpolating current. It is found that the K-N intermediate state constitutes only 10% of the sum rule so that the original claim that the parity of $Θ^+$ is negative remains valid.

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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.

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arXiv2004

Effect of the bound nucleon form factors on charged-current neutrino-nucleus scattering

We study the effect of bound nucleon form factors on charged-current neutrino-nucleus scattering. The bound nucleon form factors of the vector and axial-vector currents are calculated in the quark-meson coupling model. We compute the inclusive $^{12}$C($ν_μ,μ^-$)$X$ cross sections using a relativistic Fermi gas model with the calculated bound nucleon form factors. The effect of the bound nucleon form factors for this reaction is a reduction of $\sim$8% for the total cross section, relative to that calculated with the free nucleon form factors.

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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

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

Proper construction of the continuum in light-cone QCD sum rules

A proper way of subtracting the continuum contributions in light-cone QCD sum rules (LCQSR) is demonstrated. Specifically, we calculate the continuum corresponding to a typical OPE appearing in LCQSR by properly combining the double dispersion relation with QCD duality. We demonstrate how the subtraction terms can spuriously contribute to the sum rules. In the limit of zero external momentum, taking out the spurious continuum is found to yield the sum rules using the single-variable dispersion relation. The continuum factor constructed in this way differs from the one appearing in usual LCQSR. The difference substantially affects the extraction of hadronic parameters from the correlation function involving baryon currents.

hep-ph↗

arXiv2003

Update on pion weak decay constants in nuclear matter

The QCD sum rule calculation of the in-medium pion decay constants using pseudoscalar-axial vector correlation function, $i \int d^4x e^{ip\cdot x} < ρ| T[{\bar d}(x) i γ_5 u (x) {\bar u}(0) γ_μγ_5 d (0)] | ρ>$ is revisited. In particular, we argue that the dimension 5 condensate, $<{\bar q} (i D_0)^2 q >_N + {1\over 8} < {\bar q} g_s σ\cdot {\cal G} q >_N$, which is crucial for splitting the time ($f_t$) and space ($f_s$) components of the decay constant, is not necessarily restricted to be positive. Its positive value is found to yield a tachyonic pion mass. Using the in-medium pion mass as an input, we fix the dimension 5 condensate to be around $-0.025 {\rm GeV}^2 \sim -0.019$ GeV$^2$. The role of the $N$ and $Δ$ intermediate states in the correlation function is also investigated. The $N$ intermediate state is found not to contribute to the sum rules. For the $Δ$ intermediate state, we either treat it as a part of the continuum or propose a way to subtract explicitly from the sum rules. With (and without) explicit $Δ$ subtraction while allowing the in-medium pion mass to vary within 139 MeV $ \le m_π^* \le$ 159 MeV, we obtain $f_s/f_π= 0.37 \sim 0.78$ and $f_t / f_π= 0.63 \sim 0.79$.

hep-ph↗

arXiv2002

The F/D Ratio and Meson-Baryon Couplings from QCD Sum Rules

Coupling constants of the pseudoscalar mesons to the octet baryons are computed in the QCD sum rule approach. The pi-NN, eta-NN, pi-XiXi, eta-XiXi, pi-SigmaSigma, eta-SigmaSigma as well as pi-Lambda-Sigma couplings are studied. Determining the pertinent Dirac structure in the correlation function, we analyze the couplings in the SU(3) limit. We find the F/D ratio to be \sim 0.6-0.8 that is consistent with the SU(6) value. We also estimate the SU(3) breaking effect using a projected correlation function method.

hep-ph↗

arXiv2002

Progress in the determination of the $J/ψ-π$ cross section

Improving previous calculations, we compute the $J/ψπ\to {charmed mesons}$ cross section using QCD sum rules. Our sum rules for the $J/ψπ\to \bar{D} D^*$, $D \bar{D}^*$, ${\bar D}^* D^*$ and ${\bar D} D$ hadronic matrix elements are constructed by using vaccum-pion correlation functions, and we work up to twist-4 in the soft-pion limit. Our results suggest that, using meson exchange models is perfectly acceptable, provided that they include form factors and that they respect chiral symmetry. After doing a thermal average we get $<σ^{πJ/ψ} v>\sim 0.3$ mb at $T=150\MeV$.

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