366 research outputs found
Gluon multiplicity in coherent diffraction of onium on a heavy nucleus
We derive the cross section for the diffractive gluon production in high
energy onium-nucleus collisions that includes the low-x evolution effects in
the rapidity interval between the onium and the produced gluon and in the
rapidity interval between the gluon and the target nucleus. We analyze our
result in two limiting cases: when the onium size is much smaller than the
saturation scale and when its size is much larger than the saturation scale. In
the later case the gluon multiplicity is very small in the quasi-classical case
and increases when the low-x evolution effects in onium become significant. We
discuss the implications of our result for the RHIC, LHC and EIC phenomenology.Comment: 21 pages, 5 figure
Gluon Structure Function of a Color Dipole in the Light-Cone Limit of Lattice QCD
We calculate the gluon structure function of a color dipole in
near-light-cone SU(2) lattice QCD as a function of . The quark and
antiquark are external non-dynamical degrees of freedom which act as sources of
the gluon string configuration defining the dipole. We compute the color dipole
matrix element of transversal chromo-electric and chromo-magnetic field
operators separated along a direction close to the light cone, the Fourier
transform of which is the gluon structure function. As vacuum state in the pure
glue sector, we use a variational ground state of the near-light-cone
Hamiltonian. We derive a recursion relation for the gluon structure function on
the lattice similar to the perturbative DGLAP equation. It depends on the
number of transversal links assembling the Schwinger string of the dipole.
Fixing the mean momentum fraction of the gluons to the "experimental value" in
a proton, we compare our gluon structure function for a dipole state with four
links with the NLO \emph{MRST} 2002 and the \emph{CTEQAB-0} parameterizations
at . Within the systematic uncertainty we find rather
good agreement. We also discuss the low behavior of the gluon structure
function in our model calculation.Comment: 44 pages, 10 figures, to be in accordance with the variant submitted
to Phys. Rev.
Exotic hybrid mesons in hard electroproduction
We estimate the sizeable cross section for deep exclusive electroproduction
of an exotic hybrid meson in the Bjorken regime. The production
amplitude scales like the one for usual meson electroproduction, i.e. as
. This is due to the non-vanishing leading twist distribution amplitude
for the hybrid meson, which may be normalized thanks to its relation to the
energy momentum tensor and to the QCD sum rules technique. The hard amplitude
is considered up to next-to-leading order in and we explore the
consequences of fixing the renormalization scale ambiguity through the BLM
procedure. We study the particular case where the hybrid meson decays through a
meson pair. We discuss the generalized distribution
amplitude and then calculate the production amplitude for this process. We
propose a forward-backward asymmetry in the production of and
mesons as a signal for the hybrid meson production. We briefly comment on
hybrid electroproduction at very high energy, in the diffractive limit where a
QCD Odderon exchange mechanism should dominate. The conclusion of our study is
that hard electroproduction is a promissing way to study exotic hybrid mesons,
in particular at JLAB, HERA (HERMES) or CERN (Compass)
Exclusive photoproduction of hard dijets and magnetic susceptibility of QCD vacuum
We argue that coherent production of hard dijets by linearly polarized real
photons can provide direct evidence for chirality violation in hard processes,
the first measurement of the magnetic susceptibility of the quark condensate
and the photon distribution amplitude. It can also serve as a sensitive probe
of the generalized gluon parton distribution. Numerical calculations are
presented for HERA kinematics.Comment: 4 pages, 4 figure
The spread of the gluon k_t-distribution and the determination of the saturation scale at hadron colliders in resummed NLL BFKL
The transverse momentum distribution of soft hadrons and jets that accompany
central hard-scattering production at hadron colliders is of great importance,
since it has a direct bearing on the ability to separate new physics signals
from Standard Model backgrounds. We compare the predictions for the gluonic
k_t-distribution using two different approaches: resummed NLL BFKL and DGLAP
evolution. We find that as long as the initial and final virtualities (k_t)
along the emission chain are not too close to each other, the NLL resummed BFKL
results do not differ significantly from those obtained using standard DGLAP
evolution. The saturation momentum Q_s(x), calculated within the resummed BFKL
approach, grows with 1/x even slower than in the leading-order DGLAP case.Comment: 24 pages, 8 figures, An improved, slightly more precise NLL
resummation is used and the figures are updated accordingly. The conclusions
are unchange
Factorization and high-energy effective action
I demonstrate that the amplitude for high-energy scattering can be factorized
as a convolution of the contributions due to fast and slow fields. The fast and
slow fields interact by means of Wilson-line operators -- infinite gauge
factors ordered along the straight line. The resulting factorization formula
gives a starting point for a new approach to the effective action for
high-energy scattering in QCD.Comment: 34 pages, Latex, 13 postscript figures, submitted to PR
Chiral Perturbation Theory with tensor sources
We construct the most general chirally-invariant Lagrangian for mesons in the
presence of external sources coupled to the tensor current
\bar{\psi}\sigma_{\mu\nu}\psi. In order to have only even terms in the chiral
expansion, we consider the new source of O(p^2). With this choice, we build the
even-parity effective Lagrangian up to the p^6-order (NLO). While there are
only 4 new terms at the p^4-order, at p^6-order we find 78 terms for n_f=2 and
113 terms for n_f=3. We provide a detailed discussion on the different
mechanisms that ensure that our final set of operators is complete and
non-redundant. We also examine the odd-parity sector, to conclude that the
first operators appear at the p^8-order (NNLO).Comment: 23 pages, one figure; typos corrected, one paragraph added, new
section added, references added, published versio
Ultra-High Energy Neutrino-Nucleon Scattering and Parton Distributions at Small
The cross section for ultra-high energy neutrino-nucleon scattering is very
sensitive to the parton distributions at very small values of Bjorken x (. We numerically investigate the effects of modifying the
behavior of the gluon distribution function at very small in the DGLAP
evolution equation. We then use the Color Glass Condensate formalism to
calculate the neutrino-nucleon cross section at ultra-high energies and compare
the result with those based on modification of DGLAP evolution equation.Comment: 10 pages, 4 figures, INT-PUB-05-3
How Much of the Nucleon Spin is Carried by Glue?
We estimate in the QCD sum rule approach the amount of the nucleon spin
carried by the gluon angular momentum: the sum of the gluon spin and orbital
angular momenta. The result indicates that gluons contribute at least one half
of the nucleon spin at scale of 1 GeV^2.Comment: replaced with a couple of reference added and spell-checke
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