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Jungil Lee

Publications and source records attributed to Jungil Lee.

At least 55 records · Page 3Linked to original sources
arXiv2011

p p -> J/psi+Upsilon+X as a clean probe to the quarkonium production mechanism

We report that, unlike most inclusive quarkonium-production processes, the production rate for p p -> J/psi+Upsilon+X dominantly depends on two not well-known long-distance nonrelativistic QCD matrix elements, and at leading order in the strong coupling constant, which account for the transition probabilities of the color-octet spin-triplet heavy-quark-antiquark pairs c\bar{c}_8(^3S_1) -> J/psi and b\bar{b}_8(^3S_1) -> Upsilon, respectively. With the integrated luminosity ~ 100 fb^{-1} at the center-of-momentum energy sqrt{s}=14 TeV we expect that approximately 1900 p p -> J/psi+Upsilon+X events can be observed at the CERN Large Hadron Collider by tagging muon pairs, which are enough to probe to the color-octet mechanism. The forthcoming measurement may provide a useful constraint to resolve the decade-old puzzle for the polarization of prompt J/psi at the Fermilab Tevatron. If corresponding measured rate is significantly less than the prediction, it may imply that the current values for the color-octet matrix elements are overestimated.

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arXiv2011

Inclusive double-quarkonium production at the Large Hadron Collider

Based on the nonrelativistic QCD (NRQCD) factorization formalism, we investigate inclusive productions of two spin-triplet S-wave quarkonia pp->2J/psi+X, 2Upsilon+X, and J/psi+Upsilon+X at the CERN Large Hadron Collider. The total production rates integrated over the rapidity (y) and transverse-momentum (p_T) ranges |y|<2.4 and p_T<50 GGeV are predicted to be sigma[pp->2J/psi+X] = 22 (35) nb, sigma[pp->2Upsilon+X] = 24 (49) pb, and sigma[pp->J/psi+Upsilon+X] = 7 (13) pb at the center-of-momentum energy sqrt{s} = 7 (14) TeV. In order to provide predictions that can be useful in both small- and large-p_T regions, we do not employ the fragmentation approximation and we include the spin-triplet S-wave color-singlet and color-octet channels for each quarkonium final state at leading order in the strong coupling. The p_T distributions of pp->2J/psi+X and 2Upsilon+X in the low-p_T region are dominated by the color-singlet contributions. At leading order in the strong coupling, the color-singlet channel is absent for pp->J/psi+Upsilon+X. Therefore, the process pp->J/psi+Upsilon+X may provide a useful probe to the color-octet mechanism of NRQCD.

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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

Relativistic corrections to the axial vector and vector currents in the bar{b}c meson system at order alpha_s

We compute the short distance coefficients for the NRQCD factorization formulas of the meson-to-vacuum matrix elements for the axial vector and vector parts of the charged weak current in the $S$-wave spin-singlet and -triplet bar{b}c mesons, respectively. The computation is carried out to order alpha_s including relativistic corrections of all orders in vec{q}^{2n}, where vec{q} is the relative momentum of the bar{b} and c in the meson rest frame. The relativistic corrections at order alpha_s are new. The results reveal that the relativistic corrections to the leptonic decay rate of the B_c meson at order alpha_s or less converge rapidly, which shows a strong contrast to the uncomfortably large corrections of order alpha_s^2|vec{q}|^0. The short distance coefficients listed in this paper can be employed to compute the resummation of relativistic corrections to the phenomenological measurables that involve B_c and B_c^* production and decay.

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arXiv2010

Factorization of low-energy gluons in exclusive processes

We outline a proof of factorization in exclusive processes, taking into account the presence of soft and collinear modes of arbitrarily low energy, which arise when the external lines of the process are taken on shell. Specifically, we examine the process of e^+e^- annihilation through a virtual photon into two light mesons. In an intermediate step, we establish a factorized form that contains a soft function that is free of collinear divergences. In contrast, in soft-collinear effective theory, the low-energy collinear modes factor most straightforwardly into the soft function. We point out that the cancellation of the soft function, which relies on the color-singlet nature of the external hadrons, fails when the soft function contains low-energy collinear modes.

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arXiv2010

Factorization in exclusive quarkonium production

We present factorization theorems for two exclusive heavy-quarkonium production processes: production of two quarkonia in e^+e^- annihilation and production of a quarkonium and a light meson in B-meson decays. We describe the general proofs of factorization and supplement them with explicit one-loop analyses, which illustrate some of the features of the soft-gluon cancellations. We find that violations of factorization are generally suppressed relative to the factorized contributions by a factor v^2m_c/Q for each S-wave charmonium and a factor m_c/Q for each L-wave charmonium with L>0. Here, v is the velocity of the heavy quark or antiquark in the quarkonium rest frame, Q=sqrt{s} for e^+e^- annihilation, Q=m_B for B-meson decays, sqrt{s} is the e^+e^- center-of-momentum energy, m_c is the charm-quark mass, and m_B is the B-meson mass. There are modifications to the suppression factors if quantum-number restrictions apply for the specific process.

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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

Study of Higgs self couplings of a supersymmetric $E_6$ model at the International Linear Collider

We study the Higgs self couplings of a supersymmetric $E_6$ model that has two Higgs doublets and two Higgs singlets. The lightest scalar Higgs boson in the model may be heavier than 112 GeV, at the one-loop level, where the negative results for the Higgs search at the LEP2 experiments are taken into account. The contributions from the top and scalar top quark loops are included in the radiative corrections to the one-loop mass of the lightest scalar Higgs boson, in the effective potential approximation. The effect of the Higgs self couplings may be observed in the production of the lightest scalar Higgs bosons in $e^+e^-$ collisions at the International Linear Collider (ILC) via double Higgs-strahlung process. For the center of mass energy of 500 GeV with the integrated luminosity of 500 fb$^{-1}$ and the efficiency of 20 %, we expect that at least 5 events of the lightest scalar Higgs boson may be produced at the ILC via double Higgs-strahlung process.

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arXiv2009

Optimal spin-quantization axes for quarkonium with large transverse momentum

The gluon collision process that creates a heavy-quark-antiquark pair with small relative momentum and large transverse momentum predicts at leading-order in the QCD coupling constant that the transverse polarization of the pair should increase with its transverse momentum. Measurements at the Fermilab Tevatron of the polarization of charmonium and bottomonium states with respect to a particular spin-quantization axis are inconsistent with this prediction. However the predicted rate of approach to complete transverse polarization depends on the choice of spin-quantization axis. We introduce axes that maximize and minimize the transverse polarization from the leading-order gluon collision process. They are determined by the direction of the jet that provides most of the balancing transverse momentum.

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arXiv2009

Optimal spin-quantization axes for the polarization of dileptons with large transverse momentum

The leading-order parton processes that produce a dilepton with large transverse momentum predict that the transverse polarization should increase with the transverse momentum for almost any choice of the quantization axis for the spin of the virtual photon. The rate of approach to complete transverse polarization depends on the choice of spin quantization axis. We propose axes that optimize that rate of approach. They are determined by the momentum of the dilepton and the direction of the jet that provides most of the balancing transverse momentum.

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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

Resummation of Relativistic Corrections to e+ e- -> J/psi+eta_c

We present a new calculation, in the nonrelativistic QCD (NRQCD) factorization formalism, of the relativistic corrections to the double-charmonium cross section sigma[e+ e- -> J/psi+eta_c] at the energy of the Belle and BABAR experiments. In comparison with previous work, our calculation contains several refinements. These include the use of the improved results for the nonperturbative NRQCD matrix elements, the resummation of a class of relativistic corrections, the use of the vector-meson-dominance method to calculate the fragmentation contribution to the pure QED amplitude, the inclusion of the effects of the running of alpha, and the inclusion of the contribution that arises from the interference between the relativistic corrections and the corrections of next-to-leading order in alpha_s. We also present a detailed estimate of the theoretical uncertainty. We conclude that the discrepancy between the theoretical prediction for sigma[e+e- -> J/psi+eta_c] and the experimental measurements has been resolved.

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arXiv2008

Factorization theorems for exclusive heavy-quarkonium production

We outline the proofs of the factorization theorems for exclusive two-body charmonium production in B-meson decay and e^+e^- annihilation to all orders in perturbation theory in quantum chromodynamics. We find that factorized expressions hold up to corrections of order m_c/m_b in B-meson decay and corrections of order m_c^2/s in e^+e^- annihilation, where m_c is the charm-quark mass, m_b is the bottom-quark mass, and root-s is the e^+e^- center-of-momentum energy.

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