arXiv subjects

Hee Sok Chung

Publications and source records attributed to Hee Sok Chung.

50 records · Page 3Linked to original sources

arXiv2015

Quark fragmentation into spin-triplet $S$-wave quarkonium

We compute fragmentation functions for a quark to fragment to a quarkonium through an $S$-wave spin-triplet heavy quark-antiquark pair. We consider both color-singlet and color-octet heavy quark-antiquark ($Q\bar Q$) pairs. We give results for the case in which the fragmenting quark and the quark that is a constituent of the quarkonium have different flavors and for the case in which these quarks have the same flavors. Our results for the sum over all spin polarizations of the $Q\bar Q$ pairs confirm previous results. Our results for longitudinally polarized $Q\bar Q$ pairs agree with previous calculations for the same flavor cases and correct an error in a previous calculation for the different-flavor case.

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arXiv2014

Relativistic corrections to Higgs boson decays to quarkonia

We improve the theoretical predictions for the decays of the Higgs boson to an $S$-wave vector quarkonium plus a photon by calculating the relativistic correction of order $v^2$, where $v$ is the heavy-quark velocity in the quarkonium rest frame. Our numerical results are given for the $J/ψ$ and $Υ(nS)$ channels, with $n=1,2,3$. The numerical results include a previously calculated correction of order $α_s$ and summations, to all orders in $α_s$, of leading logarithms of $m_H^2/m_Q^2$, where $m_H$ is the Higgs-boson mass and $m_Q$ is the heavy-quark mass. These QCD corrections apply to the contribution of leading order in $v$ and to part of the order-$v^2$ correction. For the remainder of the order-$v^2$ correction, we sum leading logarithms of $m_H/m_Q$ through order $α_s^2$. These refinements reduce the theoretical uncertainties in the direct-production amplitudes for $H \to J/ψ+γ$ and $H \to Υ(1S)+γ$ by approximately a factor of 3 and open the door to improved determinations at the LHC of the Higgs-boson Yukawa couplings to the charm and bottom quarks.

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arXiv2014

Double Logarithms in $e^+ e^- \to J/ψ+ η_c$

Double logarithms of $Q^2/m_c^2$ that appear in the cross section for $e^+e^-\to J/ψ+ η_c$ at next-to-leading order (NLO) in the strong coupling $α_s$ account for the bulk of the NLO correction at $B$-factory energies. (Here, $Q^2$ is the square of the center-of-momentum energy, and $m_c$ is the charm-quark mass.) We analyze the double logarithms that appear in the contribution of each NLO Feynman diagram, and we find that the double logarithms arise from both the Sudakov and the end-point regions of the loop integration. The Sudakov double logarithms cancel in the sum over all diagrams. We show that the end-point region of integration can be interpreted as a pinch-singular region in which a spectator fermion line becomes soft or soft and collinear to a produced meson. This interpretation may be important in establishing factorization theorems for helicity-flip processes, such as $e^+e^-\to J/ψ+ η_c$, and in resumming logarithms of $Q^2/m_c^2$ to all orders in $α_s$.

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arXiv2014

Fragmentation contributions to J/psi production at the Tevatron and the LHC

We compute leading-power fragmentation corrections to $J/ψ$ production at the Tevatron and the LHC. We find that, when these corrections are combined with perturbative corrections through next-to-leading order in the strong coupling constant $α_s$, we obtain a good fit to high-$p_T$ cross section data from the CDF and CMS Collaborations. The fitted long-distance matrix elements lead to predictions of near-zero $J/ψ$ polarization in the helicity frame at large $p_T$.

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arXiv2013

Endpoint Logarithms in e+e- -> J/psi + eta_c

We investigate the origin of the double logarithms of Q^2/m_c^2 that appear in the calculation of the cross section for e+e- -> J/psi + eta_c at next-to-leading order in alpha_s. We find that, diagram-by-diagram, the double logarithms are accounted for by Sudakov double logarithms and endpoint double logarithms. The Sudakov double logarithms cancel in the sum over all diagrams, but the endpoint double logarithms do not. We reinterpret the endpoint double logarithms in terms of a leading region of loop integration in which a spectator fermion line becomes soft. This reinterpretation may simplify the process of establishing an all-orders factorization theorem for this helicity-flip process, which, in turn, might allow one to resum logarithms of Q^2/m_c^2 to all orders in alpha_s.

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arXiv2011

Polarization of prompt J/psi in pp -> J/psi+X at sqrt{s}=200 GeV

Within the framework of the nonrelativistic QCD factorization approach, we compute the cross section and polarization of prompt J/psi produced from proton-proton collisions at the center-of-momentum energy sqrt{s}=200 GeV. We present the transverse-momentum distribution in the forward-rapidity region 1.2 < |y| < 2.2 and the rapidity distribution over the transverse-momentum range 2 GeV < p_T < 20 GeV. The perturbative contributions are computed at leading order in the strong coupling constant. We predict slight transverse polarization of J/psi in the forward-rapidity region, while that for the mid-rapidity region is slightly longitudinal. The transverse-momentum distribution agrees well with the PHENIX preliminary data and the color-singlet-model prediction at next-to-leading order in alpha_s, but disagrees with the result from the leading-order color-singlet model or the s-channel-cut method.

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arXiv2011

NRQCD matrix elements for S-wave bottomonia and Gamma[eta_b(nS) -> gamma gamma] with relativistic corrections

We determine the leading-order nonrelativistic quantum chromodynamics (NRQCD) matrix element < O_1 >_Upsilon and the ratio < q^2>_Upsilon, for Upsilon=Upsilon(nS) with n=1, 2, and 3 by comparing the measured values for Gamma[Upsilon -> e^+ e^-] with the NRQCD factorization formula in which relativistic corrections are resummed to all orders in the heavy-quark velocity v. The values for < q^2 >_Upsilon, which is the ratio of order-v^2 matrix element to < O_1 >_Upsilon, are new. They can be used for NRQCD predictions involving Upsilon(nS) and eta_b(nS) with relativistic corrections. As an application, we predict the two-photon decay rates for the spin-singlet states: Gamma[eta_b(1S) -> gamma gamma] = 0.512^{+0.096}_{-0.094} keV, Gamma[eta_b(2S) -> gamma gamma] = 0.235^{+0.043}_{-0.043} keV, and Gamma[eta_b(3S) -> gamma gamma] = 0.170^{+0.031}_{-0.031} keV.

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arXiv2010

Polarization of prompt J/psi in proton-proton collisions at RHIC

Within the framework of the nonrelativistic QCD (NRQCD) factorization approach, we compute the polarization of prompt J/psi produced at the Brookhaven's Relativistic Heavy-Ion Collider from proton-proton collisions at the center-of-momentum energy sqrt{s}=200 GeV. The perturbative contributions are computed at leading order in the strong coupling constant. The prediction reveals that the color-singlet contribution severely underestimates the PHENIX preliminary data for the differential cross section integrated over the rapidity range |y|<0.35 and its contribution is strongly transversely polarized, which disagrees with the PHENIX preliminary data. After including the color-octet contributions, we find that the NRQCD predictions for both the cross section and polarization over the transverse-momentum range 1.5 GeV < p_T < 5 GeV (1.5 GeV < p_T < 2 GeV) integrated over the rapidity range |y|<0.35 (1.2 < |y| < 2.2) agree with the data within errors.

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arXiv2009

Order-alpha_s corrections to the quarkonium electromagnetic current at all orders in the heavy-quark velocity

We compute in order alpha_s the nonrelativistic QCD (NRQCD) short-distance coefficients that match quark-antiquark operators of all orders in the heavy-quark velocity v to the electromagnetic current. We employ a new method to compute the one-loop NRQCD contribution to the matching condition. The new method uses full-QCD expressions as a starting point to obtain the NRQCD contribution, thus greatly streamlining the calculation. Our results show that, under a mild constraint on the NRQCD operator matrix elements, the NRQCD velocity expansion for the quark-antiquark-operator contributions to the electromagnetic current converges. The velocity expansion converges rapidly for approximate J/psi operator matrix elements.

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arXiv2008

Exclusive heavy quarkonium + gamma production from e+ e- annihilation into a virtual photon

We compute the cross section for exclusive production of a photon associated with a heavy quarkonium H of charge-conjugation parity C=+1 from e+ e- annihilation into a virtual photon at the center-of-momentum energy root-s=10.58 GeV. The NRQCD factorization formulas for the differential and total cross sections are obtained at leading order in the strong coupling and in the relative velocity of the heavy quark in the quarkonium rest frame. The predicted cross sections for the S-wave spin-singlet cases are about 80 fb and 50 fb for H = eta_c and eta_c(2S), respectively. Among P-wave spin-triplet charmonia, chi_{c1} has a particularly large cross section of about 14 fb. The cross sections for bottomonium states eta_b and chi_{bJ} are about 3 fb. A rough estimate of the background reveals that the signal significances for charmonium processes are sufficiently large enough to be detected with ease with the integrated luminosities available at the present B factories.

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arXiv2008

Recent Developments in Heavy-Quarkonium Phenomenology

We review recent developments in heavy-quarkonium phenomenology within the nonrelativistic QCD factorization approach. Main issues we consider in this work include the polarization of prompt J/psi at the Fermilab Tevatron and the large relativistic and QCD corrections to double-charmonium production at the B factories. We also consider inclusive charm production in bottomonia decays.

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arXiv2008

Improved determination of color-singlet nonrelativistic QCD matrix elements for S-wave charmonium

We present a new computation of S-wave color-singlet nonrelativistic QCD matrix elements for the J/psi and the eta_c. We compute the matrix elements of leading order in the heavy-quark velocity v and the matrix elements of relative order v^2. Our computation is based on the electromagnetic decay rates of the J/psi and the eta_c and on a potential model that employs the Cornell potential. We include relativistic corrections to the electromagnetic decay rates, resumming a class of corrections to all orders in v, and find that they significantly increase the values of the matrix elements of leading order in v. This increase could have important implications for theoretical predictions for a number of quarkonium decay and production processes. The values that we find for the matrix elements of relative order v^2 are somewhat smaller than the values that one obtains from estimates that are based on the velocity-scaling rules of nonrelativistic QCD.

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arXiv2008

Invariant-mass distribution of cc-bar in Upsilon(1S) -> cc-bar + X

We calculate the invariant-mass distribution for the cc-bar pair produced in the inclusive Upsilon(1S) decay based on the color-singlet mechanism of the nonrelativistic quantum chromodynamics factorization approach at leading order in the bottom-quark velocity v_b in the meson rest frame. As the short-distance processes, we consider bb-bar -> g^*gg followed by g^* -> cc-bar and bb-bar -> gamma^* -> cc-bar at leading order in the strong coupling. The invariant-mass distribution of the bb-bar -> cc-bar gg contribution has a sharp peak just above the threshold and that of the bb-bar -> gamma^* -> cc-bar channel is concentrated at the maximally allowed kinematic end point. We predict that Gamma[Upsilon(1S) -> cc-bar+X]/Gamma[Upsilon(1S)->light hadrons] = 0.065 alpha_s, which is smaller than a previous result by about 20%.

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arXiv2008

Cornell Potential Parameters for S-wave Heavy Quarkonia

We compute derived quantities for various values of the model parameter of the Cornell potential model for the S-wave heavy quarkonia with radial quantum numbers n=1, 2, and 3. Our results can be used to determine leading and relative-order-v^2 nonrelativistic quantum chromodynamics matrix elements for S-wave charmonia and bottomonia such as psi(2S), eta_c(2S), and Upsilon(nS) for n=1, 2, and 3. These matrix elements will be essential ingredients for resumming relativistic corrections to processes involving those S-wave heavy quarkonium states.

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