Publications (87)257.66 Total impact

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ABSTRACT: We compute fragmentation functions for a quark to fragment to a quarkonium through an $S$wave spintriplet heavy quarkantiquark pair. We consider both colorsinglet and coloroctet heavy quarkantiquark ($Q\bar Q$) 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 are new. 
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ABSTRACT: 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 heavyquark velocity in the quarkonium rest frame. Our numerical results also include a previously calculated correction of order $\alpha_s$ and summations, to all orders in $\alpha_s$, of leading logarithms of $m_H^2/m_Q^2$, where $m_H$ is the Higgsboson mass and $m_Q$ is the heavyquark 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 $\alpha_s^2$. These refinements reduce the theoretical errors on the directproduction amplitudes for $H \to J/\psi+\gamma$ and $H \to \Upsilon+\gamma$ by approximately a factor of three and open the door to improved determinations at the LHC of the Higgsboson Yukawa couplings to the charm and bottom quarks.Physical Review D 07/2014; 90(11). DOI:10.1103/PhysRevD.90.113010 · 4.86 Impact Factor 
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ABSTRACT: Double logarithms of $Q^2/m_c^2$ that appear in the cross section for $e^+e^\to J/\psi + \eta_c$ at nexttoleading order (NLO) in the strong coupling $\alpha_s$ account for the bulk of the NLO correction at $B$factory energies. (Here, $Q^2$ is the square of the centerofmomentum energy, and $m_c$ is the charmquark mass.) We analyze the double logarithms that appear in the contribution of each of NLO Feynman diagram, and we find that the double logarithms arise from both the Sudakov and the endpoint regions of the loop integration. The Sudakov double logarithms cancel in the sum over all diagrams. We show that the endpoint region of integration can be interpreted as a pinchsingular 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 helicityflip processes, such as $e^+e^\to J/\psi + \eta_c$, and in resumming logarithms of $Q^2/m_c^2$ to all orders in $\alpha_s$. 
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ABSTRACT: We compute leadingpower fragmentation corrections to J/psi production at the Tevatron and the LHC. We find that, when these corrections are combined with perturbative corrections through nexttoleading order in the strong coupling constant alpha_s, we obtain a good fit to highp_T cross section data from the CDF and CMS collaborations. The fitted longdistance matrix elements lead to predictions of nearzero J/psi polarization in the helicity frame at large p_T.Physical Review Letters 03/2014; 113(2). DOI:10.1103/PhysRevLett.113.022001 · 7.73 Impact Factor 
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ABSTRACT: In this Snowmass White Paper, we discuss physics opportunities involving heavy quarkonia at the intensity and energy frontiers of high energy physics. We focus primarily on two specific aspects of quarkonium physics for which significant advances can be expected from experiments at both frontiers. The first aspect is the spectroscopy of charmonium and bottomonium states above the openheavyflavor thresholds. Experiments at e^+ e^ colliders and at hadron colliders have discovered many new, unexpected quarkonium states in the last 10 years. Many of these states are surprisingly narrow, and some have electric charge. The observations of these charged quarkonium states are the first definitive discoveries of manifestly exotic hadrons. These results challenge our understanding of the QCD spectrum. The second aspect is the production of heavy quarkonium states with large transverse momentum. Experiments at the LHC are measuring quarkonium production with high statistics at unprecedented values of p_T. Recent theoretical developments may provide a rigorous theoretical framework for inclusive production of quarkonia at large p_T. Experiments at the energy frontier will provide definitive tests of this framework. Experiments at the intensity frontier also provide an opportunity to understand the exclusive production of quarkonium states. 
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ABSTRACT: In this paper we discuss decays of the Higgs boson to quarkonia in association with a photon. We identify a new mechanism for producing such final states in Higgs decays that leads to predictions for the decay rates that differ by an order of magnitude from previous estimates. Although the branching ratios for these processes are still small, the processes are experimentally clean, and the H \to J/\psi+gamma decay should be observable at a 14 TeV LHC. We point out that quantum interference between two different production mechanisms makes the decay rates sensitive to the HQQbar couplings. Consequently, measurements of the H \to J/\psi+gamma decay rate would allow one to probe the Higgscharm coupling directly at the LHC. We discuss the experimental prospects for the observation of these decays and for the direct measurement of the Hccbar coupling.Physical review D: Particles and fields 06/2013; 88(5). DOI:10.1103/PhysRevD.88.053003 · 4.86 Impact Factor 
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ABSTRACT: 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 nexttoleading order in alpha_s. We find that, diagrambydiagram, 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 allorders factorization theorem for this helicityflip 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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ABSTRACT: We compute the relativistic corrections to the colorsinglet contribution to gluon fragmentation into a J/psi at relative order v^4, making use of the nonrelativistic QCD (NRQCD) factorization approach. The corresponding fullQCD process exhibits infrared divergences that manifest themselves as single and double poles in epsilon in 42epsilon dimensions. We isolate the infrareddivergent contributions and treat them analytically. In the matching of full QCD to NRQCD, the pole contributions are absorbed into longdistance NRQCD matrix elements. The renormalizations of the ultraviolet divergences of the longdistance NRQCD matrix elements involve Born and oneloop singlepole counterterm contributions and Born doublepole counterterm contributions. While the orderv^4 contribution enhances the J/psi hadroproduction rate for the colorsinglet channel substantially, this contribution is not important numerically in comparison with the coloroctet contributions. We also find that the ^3P_J coloroctet channel in the gluon fragmentation function contributes to J/psi hadroproduction significantly in comparison with the complete contribution of nexttoleading order in alpha_s in that channel. 
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ABSTRACT: We correct several errors in Phys. Rev. D 66, 094011 (2002). [arXiv:hepph/0205210].Physical review D: Particles and fields 01/2013; 87(3). DOI:10.1103/PhysRevD.87.039902 · 4.86 Impact Factor 
Article: Higherorder relativistic corrections to gluon fragmentation into spintriplet Swave quarkonium
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ABSTRACT: We compute the relativeorderv^4 contribution to gluon fragmentation into quarkonium in the 3S1 colorsinglet channel, using the nonrelativistic QCD (NRQCD) factorization approach. The QCD fragmentation process contains infrared divergences that produce single and double poles in epsilon in 42epsilon dimensions. We devise subtractions that isolate the pole contributions, which ultimately are absorbed into longdistance NRQCD matrix elements in the NRQCD matching procedure. The matching procedure involves twoloop renormalizations of the NRQCD operators. The subtractions are integrated over the phase space analytically in 42epsilon dimensions, and the remainder is integrated over the phasespace numerically. We find that the orderv^4 contribution is enhanced relative to the orderv^0 contribution. However, the orderv^4 contribution is not important numerically at the current level of precision of quarkoniumhadroproduction phenomenology. We also estimate the contribution to hadroproduction from gluon fragmentation into quarkonium in the 3PJ coloroctet channel and find that it is significant in comparison to the complete nexttoleadingorderinalpha_s contribution in that channel.Journal of High Energy Physics 08/2012; 2012(11). DOI:10.1007/JHEP11(2012)020 · 6.22 Impact Factor 
Article: Theory of Charmonium Production
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ABSTRACT: I give an overview of the current status of the theory of charmonium production in hardscattering processes and summarize the present state of comparisons between theory and experiment. 
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ABSTRACT: We calculate the NRQCD matrix elements for the decays of the lowestlying S and Pwave states of charmonium and bottomonium in quenched lattice QCD. We also compute the oneloop relations between the lattice and continuum matrix elements.International Journal of Modern Physics A 01/2012; 12(22). DOI:10.1142/S0217751X97002176 · 1.09 Impact Factor 
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ABSTRACT: I review the NRQCD factorization approach for quarkonium production and compare its predictions with measurements in hadronhadron and ep collisions. Comment: 6 pages, contribution to the proceedings of Charm 2010, IHEP, Beijing, October 2124, 201012/2010; DOI:10.1142/S201019451100050X 
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ABSTRACT: We address the possibility in factorization proofs that lowenergy collinear gluons can couple to soft gluons.11/2010; DOI:10.1063/1.3575015 
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ABSTRACT: A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$factories and CLEOc flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavyion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newlyfound quarkoniumlike states unleashed a flood of theoretical investigations into new forms of matter such as quarkgluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and inmedium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavyion collisions that have emerged from RHIC have elevated the importance of separating hot and coldnuclearmatter effects in quarkgluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.European Physical Journal C 10/2010; 71(2). DOI:10.1140/epjc/s1005201015349 · 5.44 Impact Factor 
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ABSTRACT: We present factorization theorems for two exclusive heavyquarkonium production processes: production of two quarkonia in e^+e^ annihilation and production of a quarkonium and a light meson in Bmeson decays. We describe the general proofs of factorization and supplement them with explicit oneloop analyses, which illustrate some of the features of the softgluon cancellations. We find that violations of factorization are generally suppressed relative to the factorized contributions by a factor v^2m_c/Q for each Swave charmonium and a factor m_c/Q for each Lwave 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 Bmeson decays, sqrt{s} is the e^+e^ centerofmomentum energy, m_c is the charmquark mass, and m_B is the Bmeson mass. There are modifications to the suppression factors if quantumnumber restrictions apply for the specific process. Comment: 69 pages, 12 figures, 2 tables. v2: Version published in Physical Review DPhysical review D: Particles and fields 02/2010; DOI:10.1103/PhysRevD.81.114014 · 4.86 Impact Factor 
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ABSTRACT: 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 softcollinear effective theory, the lowenergy collinear modes factor most straightforwardly into the soft function. We point out that the cancellation of the soft function, which relies on the colorsinglet nature of the external hadrons, fails when the soft function contains lowenergy collinear modes. Comment: 18 pages, 10 figures, 2 tables, version published in Physical Review DPhysical review D: Particles and fields 03/2009; DOI:10.1103/PhysRevD.81.114005 · 4.86 Impact Factor 
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ABSTRACT: We outline the proofs of the factorization theorems for exclusive twobody charmonium production in Bmeson 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 Bmeson decay and corrections of order m_{c};{2}/s in e;{+}e;{} annihilation, where m_{c} is the charmquark mass, m_{b} is the bottomquark mass, and sqrt[s] is the e;{+}e;{} centerofmomentum energy.Physical Review Letters 10/2008; 101(10):102002. DOI:10.1103/PhysRevLett.101.102002 · 7.73 Impact Factor 
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ABSTRACT: We compute in order alpha_s the nonrelativistic QCD (NRQCD) shortdistance coefficients that match quarkantiquark operators of all orders in the heavyquark velocity v to the electromagnetic current. We employ a new method to compute the oneloop NRQCD contribution to the matching condition. The new method uses fullQCD 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 quarkantiquarkoperator contributions to the electromagnetic current converges. The velocity expansion converges rapidly for approximate J/psi operator matrix elements.Physical review D: Particles and fields 08/2008; 79(1). DOI:10.1103/PHYSREVD.79.014007 · 4.86 Impact Factor 
Article: Resummation of relativistic corrections to e{sup +}e{sup } {rarrow} J/{psi} + {eta}{sub c}.
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ABSTRACT: No abstract prepared.Physical Review D 04/2008; 77(May 2008). DOI:10.1103/PhysRevD.77.094018 · 4.86 Impact Factor
Publication Stats
4k  Citations  
257.66  Total Impact Points  
Top Journals
Institutions

1990–2014

Argonne National Laboratory
 Division of High Energy Physics
Lemont, Illinois, United States


2010

University of Alberta
 Department of Physics
Edmonton, Alberta, Canada


2007

The Ohio State University
 Department of Physics
Columbus, Ohio, United States


2004–2007

Korea University
 Department of Physics
Seoul, Seoul, South Korea


1981–1989

Stanford University
 SLAC National Accelerator Laboratory
Palo Alto, California, United States


1988

University of Illinois at Chicago
 Department of Physics
Chicago, Illinois, United States
