arXiv subjects

Hee Sok Chung

Publications and source records attributed to Hee Sok Chung.

At least 19 recordsLinked to original sources

arXiv2026

$Υ(nS)$ Production within Jets at the LHC

Heavy quarkonium production inside jets offers a sensitive probe of QCD dynamics and bound-state formation mechanisms. While recent studies demonstrate that charmonium-in-jet observables effectively discriminate among competing nonrelativistic QCD (NRQCD) long-distance matrix element (LDME) sets, whether this discriminating power persists in the bottomonium sector remains an open question. Here, we present the first phenomenological study of $Υ(1S)$, $Υ(2S)$, and $Υ(3S)$ production inside jets using the fragmenting jet function (FJF) framework at next-to-leading order (NLO), incorporating DGLAP evolution, threshold resummation, and feeddown contributions from higher bottomonium states. In sharp contrast to charmonium, we find that bottomonium-in-jet momentum-fraction ($z_H$) distributions exhibit a universal shape that is remarkably insensitive to the choice of LDME sets. We show that this universality stems from the strong dominance of the S-wave spin-triplet color-octet ($^3S_1^{[8]}$) production mechanism reinforced by $χ_b$ feeddown transitions. Our predictions capture both the characteristic large-$z_H$ peak and the spectral broadening with increasing jet transverse momentum observed in recent CMS measurements. These results establish a clear physical distinction between charmonium and bottomonium fragmentation inside jets, providing a theoretical benchmark for future high-precision measurements at the LHC.

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arXiv2026

Resummation of threshold double logarithms in quarkonium fragmentation functions

We develop a formalism for resumming threshold double logarithms that appear in fragmentation functions for production of heavy quarkonia. Threshold singularities appear in fixed-order calculations of quarkonium fragmentation functions in the nonrelativistic QCD factorization formalism due to radiation of soft gluons. Because of this, fixed-order quarkonium fragmentation functions are not positive definite, and can lead to unphysically negative cross sections. This problem can be resolved by resumming threshold logarithms to all orders in perturbation theory, which renders the fragmentation functions finite and ensures the positivity of cross sections. We present a detailed derivation of the resummation formalism and derive the formula for resummed quarkonium fragmentation functions, which can be computed entirely within perturbation theory without the need for nonperturbative model functions.

hep-ph↗

arXiv2026

$J/ψ$ Production Within Jets at the EIC

We present theoretical predictions for the transverse-momentum distribution of $J/ψ$ produced within jets at the upcoming Electron-Ion Collider (EIC). Utilizing the semi-inclusive fragmenting jet function (FJF) framework, our calculation achieves next-to-leading order (NLO) accuracy in the strong coupling and leading-logarithmic (LL) accuracy by resumming both collinear and threshold logarithms. In contrast to the gluon-dominated regime of the LHC, EIC photoproduction is characterized by an enhanced quark-initiated component, offering a complementary probe into the charmonium production mechanism governed by nonperturbative long-distance matrix elements (LDMEs). We examine the impact of representative LDME sets, demonstrating the EIC's distinct discriminating power for the mechanisms. We find that quark contributions are particularly significant in the small momentum fraction region. This region is also shown to be sensitive to both the jet radius $R$ and the experimental muon identification criteria for the $J/ψ\to μ^+μ^-$ decay channel. These findings establish quarkonium-in-jet observables at the EIC as a vital, independent probe for constraining the production mechanisms and advancing our understanding of heavy quarkonium formation.

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arXiv2025

Resummation of threshold double logarithms in inclusive production of heavy quarkonium

We resum threshold double logarithms in inclusive production of heavy quarkonium that arise from singularities near the boundary of phase space. This resolves the catastrophic failure in the conventional approach based on fixed-order perturbation theory calculations in nonrelativistic QCD, where quarkonium cross sections at large transverse momentum can turn negative. We identify the root cause of this negative cross section problem as the appearance of threshold logarithms in radiative corrections, and resum them to all orders in perturbation theory at the leading double logarithmic level. We find that resummation of threshold logarithms is imperative for describing measured $J/ψ$ production rates at large transverse momentum.

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arXiv2025

Hadroproduction data support tetraquark hypothesis for $χ_{c1} (3872)$

We show that the recently proposed tetraquark hypothesis for the nature of the $χ_{c1}(3872)$ results in a formalism for inclusive production rates that has no unknown parameters. We employ this formalism to compute hadroproduction rates of $χ_{c1}(3872)$ at the Large Hadron Collider, which agree with measured prompt and nonprompt cross sections. Thus we find that the tetraquark hypothesis for $χ_{c1}(3872)$ is well supported by hadroproduction data.

hep-ph↗

arXiv2025

NRQCD Re-Confronts LHCb Data on Quarkonium Production within Jets

We compare LHCb measurements of $J/ψ$ and $ψ(2S)$ transverse momentum distributions within jets with QCD calculations, which may be crucial in understanding the quarkonium production mechanism. Our theoretical calculations are based on the fragmenting jet function formalism, while the nonperturbative formation of quarkonia is described by the nonrelativistic QCD factorization formalism. We include the newest refinements in the perturbative calculation including resummation of threshold and DGLAP logarithms. We find that the $ψ(2S)$ data has the potential to discriminate between the different production mechanisms proposed in the literature.

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arXiv2025

Resummation of threshold double logarithms in hadroproduction of heavy quarkonium

We resum threshold double logarithms that appear in inclusive production of heavy quarkonium. This resolves the catastrophic failure of fixed-order perturbation theory where quarkonium cross sections at large transverse momentum can turn negative due to large radiative corrections. We find that resummation is imperative for describing measured prompt production rates of $J/ψ$ at large transverse momentum.

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arXiv2024

Color-octet nonrelativistic QCD matrix elements for heavy quarkonium decays in the refined Gribov-Zwanziger theory

We determine color-octet nonrelativistic QCD matrix elements for quarkonium decays from moments of the two-point correlation function of the QCD field-strength tensor computed in the refined Gribov-Zwanziger theory. We find that a tree-level calculation in the refined Gribov-Zwanziger theory can give a suitable description of the QCD field-strength correlation function at both short and long distances, which leads to moments that are infrared finite and can be properly renormalized. By using the color-octet matrix elements we obtain, we quantitatively improve the nonrelativistic effective field theory description of quarkonium decay rates, especially for the $χ_{QJ}$ and $η_Q$ states, where $Q =c$ or $b$.

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arXiv2023

Mesonic decay constant and mass ratios and the conformal window

Two particular ratios related to mesons are proposed for the study of the conformal window in $SU(3)$ gauge theory and fundamental fermions. Lattice and other studies indicate that the lower end, $N_f^*$, is at around 7 - 13 flavors which is a wide range without a clear consensus. Here we propose the decay constant to mass ratios of mesons, $f_{PS,V} / m_V$, as a proxy since below the conformal window lattice studies have shown that they are largely $N_f$-independent while at the upper end of the conformal window they are vanishing. The drop from the non-zero constant value to zero at $N_f = 16.5$ might be indicative of $N_f^*$. We compute $f_V / m_V$ to N$^3$LO and $f_{PS} / m_V$ to NNLO order in (p)NRQCD. The results are unambiguously reliable just below $N_f = 16.5$, hence the results are expanded á la Banks-Zaks in $\varepsilon = 16.5 - N_f$. The convergence properties of the series and matching with the non-perturbative infinite volume, continuum and chiral extrapolated lattice results at $N_f = 10$ suggest that the perturbative results might be reliable down to $N_f = 12$. A sudden drop is observed at $N_f = 12$ and $N_f = 13$ in $f_V / m_V$ and $f_{PS} / m_V$, respectively.

hep-lat↗

arXiv2023

Resummation and renormalization of kinematical effects in inclusive $P$-wave quarkonium production

We investigate the renormalization properties of the shape function formalism for inclusive production of $P$-wave heavy quarkonia, which arises from resumming a class of corrections coming from kinematical effects associated with the motion of the heavy quark and antiquark pair relative to the quarkonium. Such kinematical effects are encoded in the nonperturbative shape functions, which are normalized to the corresponding nonrelativistic QCD long-distance matrix elements. By using the known ultraviolet divergences in the matrix elements, we derive the large-momentum asymptotic behavior of the shape functions. This strongly constrains the form of the shape functions and significantly reduces the dependence on the nonperturbative model. Based on these results we show that the shape function formalism at loop level can be useful in taming the threshold logarithms at large transverse momentum, and at small transverse momentum the kinematical corrections reduce the sizes of $χ_c$ and $χ_b$ cross sections which may improve agreement with measurements.

hep-ph↗

arXiv2023

The $f_\varrho / m_\varrho$ and $f_π/ m_\varrho$ ratios and the conformal window

The $f_\varrho / m_\varrho$ ratio is calculated at N$^3$LO order within perturbative (p)NRQCD with $N_f$ flavors of mass degenerate fermions. The massless limit of the ratio is expanded á la Banks-Zaks in $ε= 16.5 - N_f$ leading to reliable predictions close to the upper end of the conformal window. The comparison of the NNLO and N$^3$LO results indicate that the Banks-Zaks expansion may be reliable down to twelve flavors. Previous lattice calculations combined with the KSRF relations provide us with the same ratio for the range $2 \leq N_f \leq 10$. Assuming a monotonous dependence on $N_f$ leads to an estimate for the lower end of the conformal window, $N_f^* \simeq 12$, by matching the non-perturbative and our perturbative results. In any case an abrupt change is observed in $f_\varrho / m_\varrho$ at twelve flavors. As a cross-check we also consider the $f_π/ m_\varrho$ ratio for which lattice results are also available. The perturbative calculation at present is only at the NNLO level which is insufficient for a reliable and robust matching between the low $N_f$ and high $N_f$ regions. Nonetheless, using the relative size of the N$^3$LO correction of $f_\varrho / m_\varrho$ for estimating the same for $f_π/ m_\varrho$ leads to the estimate $N_f^* \simeq 13$.

hep-ph↗

arXiv2023

Inclusive production of $J/ψ$, $ψ(2S)$, and $Υ$ states in pNRQCD

Under some assumptions on the hierarchy of relevant energy scales, we compute the nonrelativistic QCD (NRQCD) long-distance matrix elements (LDMEs) for inclusive production of $J/ψ$, $ψ(2S)$, and $Υ$ states based on the potential NRQCD (pNRQCD) effective field theory. Based on the pNRQCD formalism, we obtain expressions for the LDMEs in terms of the quarkonium wavefunctions at the origin and universal gluonic correlators, which do not depend on the heavy quark flavor or the radial excitation. This greatly reduces the number of nonperturbative unknowns and substantially enhances the predictive power of the nonrelativistic effective field theory formalism. We obtain improved determinations of the LDMEs for $J/ψ$, $ψ(2S)$, and $Υ$ states thanks to the universality of the gluonic correlators, and obtain phenomenological results for cross sections and polarizations at large transverse momentum that agree well with measurements at the LHC.

hep-ph↗

arXiv2022

Quarkonium production and polarization: where do we stand?

We review the current status of heavy quarkonium production phenomenology based on nonrelativistic effective field theories, focusing on spin-triplet $S$-wave states such as $J/ψ$, $ψ(2S)$, and $Υ$. We present some representative examples for heavy quarkonium production mechanisms proposed in the literature, which vary significantly depending on the choice of data employed in analyses. We then discuss the rôle of polarization in discriminating between the different possible scenarios for quarkonium production. Other observables that may be useful in pinpointing the production mechanism are also introduced, such as the $η_c$ production, associated production of $J/ψ$ plus a gauge boson, and $J/ψ$ production at the Electron-Ion Collider.

hep-ph↗

arXiv2022

Production and polarization of $S$-wave quarkonia in potential nonrelativistic QCD

Based on the potential nonrelativistic QCD formalism, we compute the nonrelativistic QCD long-distance matrix elements (LDMEs) for inclusive production of $S$-wave heavy quarkonia. This greatly reduces the number of nonperturbative unknowns and brings in a substantial enhancement in the predictive power of the nonrelativistic QCD factorization formalism. We obtain improved determinations of the LDMEs and find cross sections and polarizations of $J/ψ$, $ψ(2S)$, and excited $Υ$ states that agree well with LHC data. Our results may have important implications in pinning down the heavy quarkonium production mechanism.

hep-ph↗

arXiv2022

QCD Static Force in Gradient Flow

We compute the QCD static force and potential using gradient flow at next-to-leading order in the strong coupling. The static force is the spatial derivative of the static potential: it encodes the QCD interaction at both short and long distances. While on the one side the static force has the advantage of being free of the $O(Λ_{\rm QCD})$ renormalon affecting the static potential when computed in perturbation theory, on the other side its direct lattice QCD computation suffers from poor convergence. The convergence can be improved by using gradient flow, where the gauge fields in the operator definition of a given quantity are replaced by flowed fields at flow time $t$, which effectively smear the gauge fields over a distance of order $\sqrt{t}$, while they reduce to the QCD fields in the limit $t \to 0$. Based on our next-to-leading order calculation, we explore the properties of the static force for arbitrary values of $t$, as well as in the $t \to 0$ limit, which may be useful for lattice QCD studies.

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arXiv2021

Inclusive Hadroproduction of $P$-wave Heavy Quarkonia in pNRQCD

We compute NRQCD long-distance matrix elements that appear in the inclusive production cross sections of $P$-wave heavy quarkonia in the framework of potential NRQCD. The formalism developed in this work applies to strongly coupled charmonia and bottomonia. This makes possible the determination of color-octet NRQCD long-distance matrix elements without relying on measured cross section data, which has not been possible so far. We obtain results for inclusive production cross sections of $χ_{cJ}$ and $χ_{bJ}$ at the LHC, which are in good agreement with measurements.

hep-ph↗

arXiv2021

$P$-wave quarkonium wavefunctions at the origin in the $\overline{\rm MS}$ scheme

We compute $P$-wave quarkonium wavefunctions at the origin in the $\overline{\rm MS}$ scheme based on nonrelativistic effective field theories. We include nonperturbative effects from the long-distance behaviors of the potential, while the short-distance behaviors are determined from perturbative QCD. We obtain $\overline{\rm MS}$-renormalized $P$-wave quarkonium wavefunctions at the origin that have the correct scale dependences that are expected from factorization formalisms, so that the dependences on the scheme and scale cancel in physical quantities. This greatly reduces the theoretical uncertainties associated with scheme and scale dependences in predictions of decay and production rates. Based on the calculation of the $P$-wave wavefunctions at the origin in this work, we make first-principles predictions of electromagnetic decay rates and exclusive electromagnetic production rates of $P$-wave charmonia and bottomonia, and compare them with measurements.

hep-ph↗

arXiv2021

Inclusive Production of Heavy Quarkonia in pNRQCD

We develop a formalism for computing inclusive production cross sections of heavy quarkonia based on the nonrelativistic QCD and the potential nonrelativistic QCD effective field theories. Our formalism applies to strongly coupled quarkonia, which include excited charmonium and bottomonium states. Analogously to heavy quarkonium decay processes, we express nonrelativistic QCD long-distance matrix elements in terms of quarkonium wavefunctions at the origin and universal gluonic correlators. Our expressions for the long-distance matrix elements are valid up to corrections of order $1/N_c^2$. These expressions enhance the predictive power of the nonrelativistic effective field theory approach to inclusive production processes by reducing the number of nonperturbative unknowns, and make possible first-principle determinations of long-distance matrix elements once the gluonic correlators are known. Based on this formalism, we compute the production cross sections of $P$-wave charmonia and bottomonia at the LHC, and find good agreement with measurements.

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