[Show abstract][Hide abstract] ABSTRACT: We compute fragmentation corrections to hadroproduction of the quarkonium
states $J/\psi$, $\chi_{cJ}$, and $\psi(2S)$ at leading power in $m_c/p_T$,
where $m_c$ is the charm-quark mass and $p_T$ is the quarkonium transverse
momentum. The computation is carried out in the framework of nonrelativistic
QCD. We include corrections to the parton-production cross sections through
next-to-leading order in the strong coupling $\alpha_s$ and corrections to the
fragmentation functions through second order in $\alpha_s$. We also sum leading
logarithms of $p_T^2/m_c^2$ to all orders in perturbation theory. We find that,
when we combined these leading-power fragmentation corrections with fixed-order
calculations through next-to-leading order in $\alpha_s$, we are able to obtain
good fits for $p_T\geq 10$ GeV to hadroproduction cross sections that were
measured at the Tevatron and the LHC. Using values for the nonperturbative
long-distance matrix elements that we extract from the cross-section fits, we
make predictions for the polarizations of the quarkonium states. We obtain good
agreement with measurements of the polarizations, with the exception of the CDF
Run II measurement of the prompt $J/\psi$ polarization, for which the agreement
is only fair. In the predictions for the prompt-$J/\psi$ cross sections and
polarizations, we take into account feeddown from the $\chi_{cJ}$ and
$\psi(2S)$ states.
[Show abstract][Hide abstract] ABSTRACT: We compute leading-power fragmentation corrections to $J/\psi$
photoproduction at DESY HERA, making use of the nonrelativistic QCD
factorization approach. Our calculations include parton production cross
sections through order $\alpha_s^3$, fragmentation functions though order
$\alpha_s^2$, and leading logarithms of the transverse momentum divided by the
charm-quark mass to all orders in $\alpha_s$. We find that the leading-power
fragmentation corrections, beyond those that are included through
next-to-leading order in $\alpha_s$, are small relative to the fixed-order
contributions through next-to-leading order in $\alpha_s$. Consequently, an
important discrepancy remains between the experimental measurements of the
$J/\psi$ photoproduction cross section and predictions that make use of
nonrelativistic-QCD long-distance matrix elements that are extracted from the
$J/\psi$ hadroproduction cross-section and polarization data.
[Show abstract][Hide abstract] ABSTRACT: 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 are new.
Physical Review D 12/2014; 91(7). DOI:10.1103/PhysRevD.91.074013 · 4.64 Impact Factor
[Show abstract][Hide abstract] 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 heavy-quark 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
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 $\alpha_s^2$. These refinements reduce
the theoretical errors on the direct-production 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 Higgs-boson
Yukawa couplings to the charm and bottom quarks.
Physical Review D 07/2014; 90(11). DOI:10.1103/PhysRevD.90.113010 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Double logarithms of $Q^2/m_c^2$ that appear in the cross section for
$e^+e^-\to J/\psi + \eta_c$ at next-to-leading 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 center-of-momentum energy, and
$m_c$ is the charm-quark 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
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
$e^+e^-\to J/\psi + \eta_c$, and in resumming logarithms of $Q^2/m_c^2$ to all
orders in $\alpha_s$.
Physical Review D 06/2014; 90(7). DOI:10.1103/PhysRevD.90.074028 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We compute leading-power fragmentation corrections to J/psi 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 alpha_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/psi polarization in the helicity frame at large p_T.
[Show abstract][Hide abstract] 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
open-heavy-flavor 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.
[Show abstract][Hide abstract] 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 Higgs-charm 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.
[Show abstract][Hide abstract] 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
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.
[Show abstract][Hide abstract] ABSTRACT: We compute the relativistic corrections to the color-singlet contribution to
gluon fragmentation into a J/psi at relative order v^4, making use of the
nonrelativistic QCD (NRQCD) factorization approach. The corresponding full-QCD
process exhibits infrared divergences that manifest themselves as single and
double poles in epsilon in 4-2epsilon dimensions. We isolate the
infrared-divergent contributions and treat them analytically. In the matching
of full QCD to NRQCD, the pole contributions are absorbed into long-distance
NRQCD matrix elements. The renormalizations of the ultraviolet divergences of
the long-distance NRQCD matrix elements involve Born and one-loop single-pole
counterterm contributions and Born double-pole counterterm contributions. While
the order-v^4 contribution enhances the J/psi hadroproduction rate for the
color-singlet channel substantially, this contribution is not important
numerically in comparison with the color-octet contributions. We also find that
the ^3P_J color-octet channel in the gluon fragmentation function contributes
to J/psi hadroproduction significantly in comparison with the complete
contribution of next-to-leading order in alpha_s in that channel.
[Show abstract][Hide abstract] ABSTRACT: We compute the relative-order-v^4 contribution to gluon fragmentation into
quarkonium in the 3S1 color-singlet channel, using the nonrelativistic QCD
(NRQCD) factorization approach. The QCD fragmentation process contains infrared
divergences that produce single and double poles in epsilon in 4-2epsilon
dimensions. We devise subtractions that isolate the pole contributions, which
ultimately are absorbed into long-distance NRQCD matrix elements in the NRQCD
matching procedure. The matching procedure involves two-loop renormalizations
of the NRQCD operators. The subtractions are integrated over the phase space
analytically in 4-2epsilon dimensions, and the remainder is integrated over the
phase-space numerically. We find that the order-v^4 contribution is enhanced
relative to the order-v^0 contribution. However, the order-v^4 contribution is
not important numerically at the current level of precision of
quarkonium-hadroproduction phenomenology. We also estimate the contribution to
hadroproduction from gluon fragmentation into quarkonium in the 3PJ color-octet
channel and find that it is significant in comparison to the complete
next-to-leading-order-in-alpha_s contribution in that channel.
Journal of High Energy Physics 08/2012; 2012(11). DOI:10.1007/JHEP11(2012)020 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: I give an overview of the current status of the theory of charmonium
production in hard-scattering processes and summarize the present state of
comparisons between theory and experiment.
[Show abstract][Hide abstract] ABSTRACT: We calculate the NRQCD matrix elements for the decays of the lowest-lying S- and P-wave states of charmonium and bottomonium in quenched lattice QCD. We also compute the one-loop relations between the lattice and continuum matrix elements.
International Journal of Modern Physics A 01/2012; 12(22). DOI:10.1142/S0217751X97002176 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: I review the NRQCD factorization approach for quarkonium production and
compare its predictions with measurements in hadron-hadron and ep collisions.
[Show abstract][Hide abstract] ABSTRACT: We address the possibility in factorization proofs that low-energy collinear
gluons can couple to soft gluons.
[Show abstract][Hide abstract] 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 CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion 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 newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium 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 heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon 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/s10052-010-1534-9 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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. Comment: 69 pages, 12 figures, 2 tables. v2: Version published in Physical Review D
[Show abstract][Hide abstract] 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 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. Comment: 18 pages, 10 figures, 2 tables, version published in Physical Review D
[Show abstract][Hide abstract] ABSTRACT: 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 sqrt[s] is the e;{+}e;{-} center-of-momentum energy.