479 research outputs found

### Spin correlations and velocity-scaling in color-octet NRQCD matrix elements

We compute spin-dependent decay matrix elements for S-wave charmonium and
bottomonium in lattice nonrelativistic quantum chromodynamics (NRQCD).
Particular emphasis is placed upon the color-octet matrix elements, since the
corresponding production matrix elements are expected to appear in the dominant
contributions to the production cross sections at large transverse momenta. We
use three slightly different versions of the heavy-quark lattice Green's
functions in order to minimize the contributions that scale as powers of the
ultraviolet cutoff. The lattice matrix elements that we calculate obey the
hierarchy that is suggested by the velocity-scaling rules of NRQCD.Comment: 25 pages, 2 figures, 2 tables, further discussion of effective
lattice cutoffs and uncertainties, additional minor revisions, version to be
published in Phys. Rev.

### Lattice Calculation of Quarkonium Decay Matrix Elements

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.Comment: 10 pages, LaTeX. Talk presented at the Quarkonium Physics Workshop,
University of Illinois, Chicago, June 13-15, 199

### 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.Comment: 31 pages, minor corrections, version published in Phys. Rev.

### 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.Comment: 31 pages, 2 figures, minor corrections, version published in Phys.
Rev.

### The Color-Octet intrinsic charm in $\eta^\prime$ and $B\to \eta^\prime X$ decays

Color-octet mechanism for the decay B\to \eta^\prime X is proposed to explain
the large branching ratio of Br(B\to \eta^\prime X)\sim 1\times 10^{-3}
recently announced by CLEO. We argue that the inclusive \eta^\prime production
in B decays may dominantly come from the Cabbibo favored b\to (\bar c c)_8s
process where \bar c c pair is in a color-octet configuration, and followed by
the nonperturbative transition (\bar c c)_8\to \eta^\prime X. The color-octet
intrinsic charm component in the higher Fock states of \eta^\prime is crucial
and is induced by the strong coupling of \eta^\prime to gluons via QCD axial
anomaly.Comment: 9 pages, RevTex, 1 PS figur

### Double charmonium production at B-factories within light cone formalism

This paper is devoted to the study of the processes e^+e^- \to J/\Psi \eta_c,
J/\Psi \eta_c', \psi' \eta_c, \psi' \eta_c' within light cone formalism. It is
shown that if one disregards the contribution of higher fock states, the
twist-3 distribution amplitudes needed in the calculation can be unambiguously
determined from the twist-2 distribution amplitudes and equations of motion.
Using models of the twist-2 distribution amplitudes the cross sections of the
processes under study have been calculated. The results of the calculation are
in agreement with Belle and BaBar experiments. It is also shown that
relativistic and radiative corrections to the cross sections play crucial role
in the achievement of the agreement between the theory and experiments. The
comparison of the results of this paper with the results obtained in other
papers has been carried out. In particular, it is shown that the results of
papers where relativistic and radiative corrections were calculated within
NRQCD are overestimated by a factor of ~1.5.Comment: 14 pages, 1 figur

### Color Octet Contribution to High p_T J/\Psi Production in pp Collisions at \sqrt s = 500 and 200 GeV at RHIC

We compute \frac{d\sigma}{dp_T} of the J/\psi production in pp collisions at
RHIC at \sqrt s = 500 and 200 GeV by using both the color octet and singlet
models in the framework of non-relativistic QCD. The J/\psi we compute here
includes the direct J/\psi from the partonic fusion processes and the J/\psi
coming from the radiative decays of \chi_J's both in the color octet and
singlet channel. The high p_T J/\psi production cross section is computed
within the PHENIX detector acceptance ranges: -0.35 < \eta < 0.35 and 1.2 <
\|\eta| < 2.4, the central electron and forward muon arms. It is found that the
color octet contribution to J/\psi production is dominant at RHIC energy in
comparison to the color singlet contributions. We compare our results with the
recent preliminary data obtained by PHENIX detector for the high p_T J/\psi
measurements. While the color singlet model fails to explain the data
completely the color octet model is in agreement with the single data point
above 2 GeV transverse momentum. A measurement of J/\psi production at RHIC in
the next run with better statistics will allow us to determine the validity of
the color octet model of J/\psi production at RHIC energies. This is very
important because it is necessary to know the exact mechanism for J/\psi
production in pp collisions at RHIC if one is to make predictions of J/\psi
suppression as a signature of quark-gluon plasma. These mechanisms also play an
important role in determining the polarized spin structure function of the
proton at RHIC.Comment: 16 pages latex, 6 figure

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### A lattice formulation of chiral gauge theories

We present a method for implementing gauge theories of chiral fermions on the lattice. Discussed topics include: the lattice as a UV regulator, a chiral QED model, modification of the fermion determinant, large gauge-field momenta, and a non-perturbative problem

### Photoproduction of h_c

Using the NRQCD factorization formalism, we calculate the total cross section
for the photoproduction of h_c mesons. We include color-octet and color-singlet
mechanisms as well as next-to-leading order perturbative QCD corrections. The
theoretical prediction depends on two nonperturbative matrix elements that are
not well determined from existing data on charmonium production. For reasonable
values of these matrix elements, the cross section is large enough that the h_c
may be observable at the E831 experiment and at the HERA experiments.Comment: Revtex file 8 pages, 1 figure. Macros needed: epsf,floats,rotate
Minor typos changed, and reference added. Version to be published in
Phys.Rev.

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