arXiv subjects

Su Houng Lee

Publications and source records attributed to Su Houng Lee.

At least 145 records · Page 8Linked to original sources

arXiv2007

J/psi hadron interaction in vacuum and in QGP

Motivated by the recent lattice data that $J/ψ$ will survive up to 1.6$T_c$, we calculate the thermal width of $J/ψ$ at finite temperature in perturbative QCD. The inputs of the calculation are the parton quarkonium dissociation cross sections at the NLO in QCD, which were previously obtained by Song and Lee, and a gaussian charmonium wave function, whose size were fitted to an estimate by Wong by solving the schrodinger equation for charmonium in a potential extracted from the lattice at finite temperature. We find that the total thermal width above 1.4$T_c$ becomes larger than 100 to 200 MeV, depending on the effective thermal masses of the quark and gluon, which we take it to vary from 600 to 400 MeV.

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arXiv2006

Anti-charmed pentaquark from B decays

We explore the possibility of observing the anti-charmed pentaquark state from the $Θ_c \bar{n} π^+$ decay of $B$ meson produced at $B$-factory experiments. We first show that the observed branching ratio of the $B^+$ to $ Λ^-_c p π^+$, as well as its open histograms, can be remarkably well explained by assuming that the decay proceeds first through the $π^+ \bar{D}^0$ (or $\bar{D}^{*0}$) decay, whose branching ratios are known, and then through the subsequent decay of the virtual $\bar{D}^0$ or $\bar{D}^{*0}$ mesons to $Λ_c^- p$, whose strength are calculated using previously fit hadronic parameters. We then note that the $Θ_c$ can be similarly produced when the virtual $\bar{D}^0$ or $\bar{D}^{*0}$ decay into an anti-nucleon and a $Θ_c$. Combining the present theoretical estimates for the ratio $g_{D N Λ_c} / g_{D N Θ_c} \sim 13 $ and $g_{D^* N Θ_c} \sim {1/3} g_{D N Θ_c}$, we find that the anti-charmed pentaquark $Θ_c$, which was predicted to be bound by several model calculations, can be produced via $B^+ \to Θ_c \bar{n} π^+$, and be observed from the $B$-factory experiments through the weak decay of $Θ_c \to p K^+ π^- π^- $.

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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

Quarkonium-Hadron Interactions in Perturbative QCD

The next to leading order (NLO) quarkonium-hadron cross section is calculated in perturbative QCD. The corresponding leading order (LO) result was performed by Peskin more than 20 years ago using the operator product expansion (OPE). In this work, the calculation is performed using the Bethe-Salpeter amplitude and the factorization formula. The soft divergence appearing in the intermediate stages of the calculations are shown to vanish after adding all possible crossed terms, while the collinear divergences are eliminated by mass factorization. Applying the result to the Upsilon system, one finds that there are large higher order correction near the threshold. The relevance of the present result to the charmonium case is also discussed.

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arXiv2005

Non-interacting KN contribution in the QCD sum rule for the pentaquark Theta^+(1540)

We perform a QCD sum rule analysis for the pentaquark baryon Theta^+ with the non-interacting $KN$ contribution treated carefully. The coupling of the Theta^+ current to the $KN$ state is evaluated by applying the soft kaon theorem and vacuum saturation. When using a five-quark current including scalar and pseudo-scalar diquarks, the KN contribution turns out not to be very important and the previous result of the negative parity Theta^+ is reproduced again. The Borel analysis of the correlation function for Theta^+ with the KN continuum states subtracted yields the mass of the J^P= 1/2^- Theta^+ around 1.5 GeV.

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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

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.

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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.

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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.

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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.

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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.

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arXiv2003

The mass of charmonium in nuclear matter

The masses of charmonium states immersed in nuclear matter are calculated in LO QCD and in QCD sum rules. While the mass shift for $J/ψ$ are found to be less than -10 MeV, those for the $χ_{0,1,2}$ and $ψ(3686)$ and $ψ(3770)$ are found to be more than -40 MeV. We investigate the feasibility of observing such mass shifts in the future accelerator project at GSI.

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arXiv2003

Charm production from proton-proton collisions

We evaluate the cross sections for charmed hadron production from proton-proton reactions $pp\to\bar D^0pΛ_c^+$ and $pp\to\bar D^{*0}pΛ_c^+$ using a hadronic Lagrangian. With empirical coupling constants and cutoff parameters in the form factors, sum of their cross sections at center-of-mass energy of 11.5 GeV is about 1 $μ$b and is comparable to measured inclusive cross section for charmed hadron production from proton-proton reactions. The cross section decreases to about 1 nb at 40 MeV above threshold.

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arXiv2003

$J/ψ$ dissociation by pions in QCD

We compute the $J/ψπ\to {charmed mesons}$ cross section using QCD sum rules. This cross section is important to distinguish the suppression in the production of $J/ψ$ through the dissociation by comoving pions and through the formation of quark-gluon plasma. 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. After doing a thermal average we get $<σ^{πJ/ψ} v>\sim 0.2 - 0.4$ mb at $T=150\MeV$

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arXiv2003

Charmonium mass in nuclear matter

The mass shift of charmonium states in nuclear matter is studied in the perturbative QCD approach. The leading-order effect due to the change of gluon condensate in nuclear matter is evaluated using the leading-order QCD formula, while the higher-twist effect due to the partial restoration of chiral symmetry is estimated using a hadronic model. We find that while the mass of $J/ψ$ in nuclear matter decreases only slightly, those of $ψ(3686)$ and $ψ(3770)$ states are reduced appreciably. Experimental study of the mass shift of charmonium states in nuclear matter can thus provide valuable information on the changes of the QCD vacuum in nuclear medium.

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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.

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arXiv2003

Charm production from photo-nucleon reaction in a hadronic model

We study the total cross section for photo production of open charm hadrons near threshold using a hadronic Lagrangian. Both two-body final states involving $Λ_c$ and a charmed meson as well as three-body final states involving nucleon and a charm-anticharm meson pair are included. With appropriate cut-off parameters in the form factors at interaction vertices, the model gives a total cross section that is consistent with the measured data at center-of-mass energy of 6 GeV. The result is compared with the prediction from the leading-order perturbative QCD.

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