arXiv subjects

Su Houng Lee

Publications and source records attributed to Su Houng Lee.

At least 163 records · Page 9Linked to original sources

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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arXiv2002

D mesons in matter and the in-medium properties of charmonium

We study the changes in the partial decay widths of excited charmonium states into $D \bar{D}$, when the D meson mass decreases in nuclear matter, taking the internal structure of the hadrons into account. Calculations within the 3P0 model for $ψ(3686)$ and $ψ(3770)$ imply that naive estimates of the in-medium widths based only on phase space are grossly exaggerated. Due to nodes in the wave functions, these states may even become narrow at high densities, if the D meson mass is decreased by about 200 MeV. For the $χ$ states, we generally expect stronger modifications of the widths. The relevance of the $χ$ widths for $J/ψ$ suppression in heavy ion collision is discussed. These phenomena could be explored in experiments at the future accelerator facility at GSI.

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arXiv2002

Form-factor dependence of the J/psi dissociation cross sections in meson exchange model

The $J/ψ$ dissociation by $π$ and $ρ$ mesons is examined in meson exchange model and compared to the quark interchange model. We found that the main difference between the predictions of the two models could be resolved by the form factors and the contact interactions in meson exchange model calculations. By adopting covariant form factors and adjusting the four-point couplings, we found that the meson exchange model could give similar predictions with the quark interchange models not only for the magnitudes but also for the energy dependence of the low-energy dissociation cross sections of the $J/ψ$ by $π$ and $ρ$ mesons. Our finding suggests a way to understand one of the discrepancies among the existing model predictions on the $J/ψ$ dissociation cross sections by light hadrons.

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arXiv2002

Quarkonium-hadron interactions in QCD

The leading order non-relativistic QCD result for the quarkonium-hadron interaction cross section is derived by using the QCD factorization formula combined with the Bethe-Salpeter amplitude for the heavy quark bound state. Our result shows the equivalence of this approach with the operator product expansion even for the bound state scattering to leading order in QCD. We also apply the formula to the charmonium system and investigate the relativistic correction coming from the phase space of the reaction. We find that although $J/ψ$-gluon cross-section gets a large relativistic correction at higher energies, the correction becomes small in the $J/ψ$-hadron cross section due to the increase of the gluon distribution at smaller $x$ inside the hadron.

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arXiv2002

Charmonium-hadron interactions from QCD

The heavy quark system is an excellent probe to learn about the QCD dynamics at finite density. First, we discuss the properties of the $J/ψ$ and $D$ meson at finite nucleon density. We discuss why their properties should change at finite density and then introduce an exact QCD relation among these hadron properties and the energy momentum tensor of the medium. Second, we discuss attempts to calculate charmonium-hadron total cross section using effective hadronic models and perturbative QCD. We emphasize a recent calculation, where the cross section is derived using QCD factorization theorem. We conclude by discussing some challenges for SIS 200.

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arXiv2001

BRST symmetries in SU(3) linear sigma model

We study the BRST symmetries in the SU(3) linear sigma model which is constructed through introduction of a novel matrix for the Goldstone boson fields satisfying geometrical constraints embedded in SU(2) subgroup. To treat these constraints we exploit the improved Dirac quantization scheme. We also discuss phenomenological aspacts in the mean field approach to this model.

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arXiv2001

Couplings between pion and charmed mesons

We compute the couplings $DD^*π$,$D_1D^*π$,$D^*D^*π$, $D_1 D_1π$ using QCD sum rules. These couplings are important inputs in the meson exchange model calculations used to estimate the amount of $J/ψ$ absorption due to pions and rho mesons in heavy ion collisions. Our sum rules are constructed at the first order in the pion momentum $p_μ$, which give the couplings that are not trivially related to the soft-pion theorem. Our calculated couplings, which somewhat depend upon the values of the heavy meson decay constants, are $g_{DD^*π}=8.2 \pm 0.1$, $g_{D_1 D^* π} = 15.8 \pm 2 {\rm GeV}$, $g_{D^* D^* π}= 0.3 \pm 0.03$ and $g_{D_1 D_1 π}= 0.17 \pm 0.04$.

hep-ph↗

arXiv2001

QCD sum rules for J/psi in the nuclear medium: calculation of the Wilson coefficients of gluon operators up to dimension 6

We calculate the Wilson coefficients of all dimension 6 gluon operators with non zero spin in the correlation function between two heavy vector currents. For the twist-4 part, we first identify the three independent gluon operators, and then proceed with the calculation of the Wilson coefficients using the fixed point gauge. Together with the previous calculation of the Wilson coefficients for the dimension 6 scalar gluon operators by Nikolaev and Radyushkin, our result completes the list of all the Wilson coefficients of dimension 6 gluon operators in the correlation function between heavy vector currents. We apply our results to investigate the mass of $J/ψ$ in nuclear matter using QCD sum rules. Using an upper bound estimate on the matrix elements of the dimension 6 gluon operators to linear order in density, we find that the density dependent contribution from dimension 6 operators is less than 40% of the dimension 4 operators with opposite sign. The final result gives about -4 MeV mass shift for the charmonium at rest in nuclear matter.

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arXiv2000

J/psi absorption by pi and rho mesons in a meson exchange model with anomalous parity interactions

We reanalyze the dissociation process of the $J/ψ$ by $π$ and $ρ$ mesons into $D + \bar{D}$, $D^* + \bar{D}$, $D + \bar{D}^*$, and $D^* + \bar{D}^*$ within a meson exchange model. In addition to the dissociation mechanisms considered in the literature, we consider anomalous parity interactions, whose couplings are constrained by heavy quark spin symmetry and phenomenology. This opens new dissociation channels and adds new diagrams in the previously considered processes. Compared to the previous results, we find that these new additions have only a minor effect on the $ρ+ J/ψ$ total inelastic cross section, but reduce the one for $π+ J/ψ$ by about 50 % near the threshold.

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arXiv2000

Gluonic Correlations in Matter

We derive the analogue of the QCD low energy theorems for the scalar and pseudoscalar gluonic correlators in nuclear matter. We find that the scalar correlations are depleted while the pseudoscalar correlations are enhanced to leading order in the nuclear matter density. We briefly discuss the consequences of these findings on the QCD spectrum.

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arXiv2000

The $F/D$ ratio and meson-baryon couplings from QCD sum rules-II

Using QCD sum rules, we compute the diagonal meson-baryon couplings, $πNN$, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$, from the baryon-baryon correlation function with a meson, $i\int d^4x e^{iq\cdot x} < 0| T J_B(x) {\bar J}_B(0)|M(p)>$. The calculations are performed to leading order in $p_μ$ by considering the two separate Dirac structures, $i γ_5 γ_μp^μ$ and $γ_5 σ_{μν} {q^μp^ν}$ separately. We first improve the previous sum rule calculations on these Dirac structures for the $πNN$ coupling by including three-particle pion wave functions of twist 4 and then extend the formalism to calculate the other couplings, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$. In the SU(3) symmetric limit, we identify the terms responsible for the $F/D$ ratio in the OPE by matching the obtained couplings with their SU(3) relations. Depending on the Dirac structure considered, we find different identifications for the $F/D$ ratio. The couplings including the SU(3) breaking effects are also discussed within our approach.

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arXiv1999

f_K/f_pi ratio from QCD sum rules

Using the correlation function of the axial vector mesons, we present a QCD sum rule calculation for the decay constants f_pi and f_K. Our calculations are only weakly dependent on the SU(3) breaking-parameter for the QCD vacuum and give the ratio f_K/f_pi = 1.11 $\pm$ 0.02.

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arXiv1999

Meson-baryon couplings and the $F/D$ ratio from QCD sum rules

Motivated by the recent work on the calculation of the $πNN$ coupling constant using QCD sum rule beyond the chiral limit, we construct the corresponding sum rules for the couplings, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$. In constructing the $η$-baryon sum rules, we use the second moment of the $η$ wave function, which we obtain from the pion wave function after SU(3) rotation. In the SU(3) symmetric limit, we can identify the term responsible for the $F/D$ ratio in the OPE, which after the sum rule analysis gives $F/D\sim 0.2$, a factor of 3 smaller than from other studies. We also present a qualitative analysis including the SU(3) breaking terms.

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arXiv1999

Two-point correlation function with pion in QCD sum rules

Within the framework of the conventional QCD sum rules, we study the pion two-point correlation function, $i\int d^4x e^{iq\cdot x} < 0| T J_N(x) {\bar J}_N(0)|π(p)>$, beyond the soft-pion limit. We construct sum rules from the three distinct Dirac structures, $i γ_5 \notp, i γ_5, γ_5 σ_{μν} {q^μp^ν}$ and study the reliability of each sum rule. The sum rule from the third structure is found to be insensitive to the continuum threshold, $S_π$, and contains relatively small contribution from the undetermined single pole which we denote as $b$. The sum rule from the $i γ_5$ structure is very different even though it contains similar contributions from $S_π$ and $b$ as the ones coming from the $γ_5 σ_{μν} {q^μp^ν}$ structure. On the other hand, the sum rule from the $i γ_5 \notp$ structure has strong dependence on both $S_π$ and $b$, which is clearly in constrast with the sum rule for $γ_5 σ_{μν} {q^μp^ν}$. We identify the source of the sensitivity for each of the sum rules by making specific models for higher resonance contributions and discuss the implication.

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arXiv1999

Vector mesons in dense matter

We will summarize the progress in understanding the changes in the vector meson spectral density in nuclear medium using the constraint equations obtained from the Borel transformed dispersion relation and QCD Operator Product Expansion. We will discuss the results for the scalar mass shift and dispersion effects (three momentum dependence) for the light quark system ($ρ, ω$), the strange quark system ($ϕ$) and the heavy quark system ($J/ψ$) in nuclear medium. For the light quark systems, a nontrivial change in the mass and width are expected, while the dispersion effects are found to be small. Existing model calculations for the dispersion effects are compared to the constraint equation in detail. Very small, but accurate mass shift is obtained for the heavy quark system.

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arXiv1999

Constraints on vector mesons with finite momentum in nuclear matter

Using the QCD operator product expansion, we derive the real part of the transverse and longitudinal vector-vector correlation function with the quantum numbers of the rho and omega mesons to leading order in density and three momentum (q^2) for energy $ω^2 --> -\infty $. The operator product expansion provides, through the Borel transformed energy dispersion relation, a model independent constraint for the momentum dependence of the vector meson spectral density in nuclear matter. Existing model calculations for the dispersion effect of the rho meson, where the vector-meson nucleon scattering amplitude is obtained by resonance saturation in the s-channel, in general violate this constraint. We trace this to an inconsistent choice for the form factor of the $ΔNρ$ vertex. With a consistent choice, where both the form factor and the coupling constant are obtained from the Bonn potential, the contribution of the $Δ$ is substantially reduced and we find good agreement with the constraint equation. We briefly comment on the implications of our result for attempts to interpret the enhancement of low-mass dileptons in heavy-ion collisions.

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arXiv1999

QCD sum rule calculation of the $πNN$ coupling-revisited

In the conventional QCD sum rule calculation for the $πNN$ coupling beyond the soft-pion limit, there are three distinct Dirac structures, each of which can be used to construct separate sum rule. We point out subtleties in the previous sum rule results, based on one of the Dirac structure, associated with using either the PV or the PS coupling schemes in modeling the phenomenological side. We propose a sum rule coming from a different Dirac structure, which is independent of the coupling schemes used and has less uncertainty in the OPE. The obtained value is $g_{πN}=9.76 \pm 2.04$ where the uncertainty mainly comes from the quark-gluon mixed condensate.

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arXiv1999

QCD sum rules with two-point correlation function

We construct three different sum rules from the two-point correlation function with pion, $i\int d^4x e^{iq\cdot x} <0| T J_N(x) {\bar J}_N(0)|π(p)>$, beyond the soft-pion limit. The PS and PV coupling schemes in the construction of the phenomenological side are carefully considered in each sum rule. We discuss the dependence of the result on the specific Dirac structure and identify the source of the dependence by making specific models for higher resonances.

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