14,448 research outputs found
Inclusive Gluon Production In High Energy Onium-Onium Scattering
We calculate the inclusive single-gluon production cross section in high
energy onium-onium scattering including pomeron loop effects. The resulting
inclusive cross section is given by the k_T-factorization formula with one of
the unintegrated gluon distribution functions depending on the total
onium-onium scattering cross section, which includes all pomeron loops and has
to be found independently. We discuss the limits of applicability of our result
and argue that they are given by the limits of applicability of pomeron loop
resummation approach. Since the obtained k_T-factorization formula is infrared
divergent we conclude that, in order to consistently calculate the
(infrared-finite) gluon production cross section in onium-onium scattering, one
has to include corrections going beyond the pomeron loop approximation.Comment: 20 pages, 6 figures; v2: version accepted to Phys. Rev. D, minor
corrections include
JIMWLK evolution in the Gaussian approximation
We demonstrate that the Balitsky-JIMWLK equations describing the high-energy
evolution of the n-point functions of the Wilson lines (the QCD scattering
amplitudes in the eikonal approximation) admit a controlled mean field
approximation of the Gaussian type, for any value of the number of colors Nc.
This approximation is strictly correct in the weak scattering regime at
relatively large transverse momenta, where it reproduces the BFKL dynamics, and
in the strong scattering regime deeply at saturation, where it properly
describes the evolution of the scattering amplitudes towards the respective
black disk limits. The approximation scheme is fully specified by giving the
2-point function (the S-matrix for a color dipole), which in turn can be
related to the solution to the Balitsky-Kovchegov equation, including at finite
Nc. Any higher n-point function with n greater than or equal to 4 can be
computed in terms of the dipole S-matrix by solving a closed system of
evolution equations (a simplified version of the respective Balitsky-JIMWLK
equations) which are local in the transverse coordinates. For simple
configurations of the projectile in the transverse plane, our new results for
the 4-point and the 6-point functions coincide with the high-energy
extrapolations of the respective results in the McLerran-Venugopalan model. One
cornerstone of our construction is a symmetry property of the JIMWLK evolution,
that we notice here for the first time: the fact that, with increasing energy,
a hadron is expanding its longitudinal support symmetrically around the
light-cone. This corresponds to invariance under time reversal for the
scattering amplitudes.Comment: v2: 45 pages, 4 figures, various corrections, section 4.4 updated, to
appear in JHE
Properties of inclusive hadron production in Deep Inelastic Scattering on heavy nuclei at low x
In this paper we present a comprehensive study of inclusive hadron production
in DIS at low . Properties of the hadron spectrum are different in different
kinematic regions formed by three relevant momentum scales: photon virtuality
, hadron transverse momentum and the saturation momentum .
We investigate each kinematic region and derive the corresponding asymptotic
formulas for the cross section at the leading logarithmic order. We also
analyze the next-leading-order (NLO) corrections to the BFKL kernel that are
responsible for the momentum conservation. In particular, we establish the
asymptotic behavior of the forward elastic dipole--nucleus scattering amplitude
at high energies deeply in the saturation regime and a modification of the
pomeron intercept. We study the nuclear effect on the inclusive cross section
using the nuclear modification factor and its logarithmic derivative. We argue
that the later is proportional to the difference between the anomalous
dimension of the gluon distribution in nucleus and in proton and thus is a
direct measure of the coherence effects. To augment our arguments and present
quantitative results we performed numerical calculations in the kinematic
region that may be accessible by the future DIS experiments.Comment: 29 pages, 8 figure
Forward gluon production in hadron-hadron scattering with Pomeron loops
We discuss new physical phenomena expected in particle production in
hadron-hadron collisions at high energy, as a consequence of Pomeron loop
effects in the evolution equations for the Color Glass Condensate. We focus on
gluon production in asymmetric, `dilute-dense', collisions : a dilute
projectile scatters off a dense hadronic target, whose gluon distribution is
highly evolved. This situation is representative for particle production in
proton-proton collisions at forward rapidities (say, at LHC) and admits a
dipole factorization similar to that of deep inelastic scattering (DIS). We
show that at sufficiently large forward rapidities, where the Pomeron loop
effects become important in the evolution of the target wavefunction, gluon
production is dominated by `black spots' (saturated gluon configurations) up to
very large values of the transverse momentum, well above the average saturation
momentum in the target. In this regime, the produced gluon spectrum exhibits
diffusive scaling, so like DIS at sufficiently high energy.Comment: 29 pages, 7 figure
Odderon and seven Pomerons: QCD Reggeon field theory from JIMWLK evolution
We reinterpret the JIMWLK/KLWMIJ evolution equation as the QCD Reggeon field
theory (RFT). The basic "quantum Reggeon field" in this theory is the unitary
matrix which represents the single gluon scattering matrix. We discuss the
peculiarities of the Hilbert space on which the RFT Hamiltonian acts. We
develop a perturbative expansion in the RFT framework, and find several
eigenstates of the zeroth order Hamiltonian. The zeroth order of this
perturbation preserves the number of - channel gluons. The eigenstates have
a natural interpretation in terms of the - channel exchanges. Studying the
single - channel gluon sector we find the eigenstates which include the
reggeized gluon and five other colored Reggeons. In the two ( - channel)
gluon sector we study only singlet color exchanges. We find five charge
conjugation even states. The bound state of two reggeized gluons is the
standard BFKL Pomeron. The intercepts of the other Pomerons in the large
limit are where is the intercept of the BFKL
Pomeron, but their coupling in perturbation theory is suppressed by at least
relative to the double BFKL Pomeron exchange. For the Pomeron
we find . We also find three charge
conjugation odd exchanges, one of which is the unit intercept
Bartels-Lipatov-Vacca Odderon, while another one has an interecept greater than
unity. We explain in what sense our calculation goes beyond the standard
BFKL/BKP calculation. We make additional comments and discuss open questions in
our approach.Comment: 58 pages, 4 figures, Extended version. To appear in JHE
JIMWLK evolution for multi-particle production in Langevin form
Within the effective theory for the Color Glass Condensate, we study
multi-particle production with rapidity correlations in proton-nucleus
collisions at high energy. The high-energy evolution responsible for such
correlations is governed by a generalization of the JIMWLK equation which
describes the simultaneous evolution of the (strong) nuclear color fields in
the direct amplitude and the complex conjugate amplitude. This functional
equation can be used to derive ordinary evolution equations for the
cross-sections for particle production (a generalization of the Balitsky
hierarchy). However, the ensuing equations appear to be too complicated to be
useful in practice, including in the limit where the number of colors is large.
To circumvent this problem, we propose an alternative formulation of the
high-energy evolution as a Langevin process, which is better suited for
numerical implementations. This process is directly oriented towards the
calculation of the cross-sections, so its detailed structure depends upon the
nature of the final state. We present the stochastic equations appropriate for
two gluon production, and also for three gluon production, with generic
rapidity differences.Comment: 28 pages, 5 figure
Decomposition of the QCD String into Dipoles and Unintegrated Gluon Distributions
We present the perturbative and non-perturbative QCD structure of the
dipole-dipole scattering amplitude in momentum space. The perturbative
contribution is described by two-gluon exchange and the non-perturbative
contribution by the stochastic vacuum model which leads to confinement of the
quark and antiquark in the dipole via a string of color fields. This QCD string
gives important non-perturbative contributions to high-energy reactions. A new
structure different from the perturbative dipole factors is found in the
string-string scattering amplitude. The string can be represented as an
integral over stringless dipoles with a given dipole number density. This
decomposition of the QCD string into dipoles allows us to calculate the
unintegrated gluon distribution of hadrons and photons from the dipole-hadron
and dipole-photon cross section via kT-factorization.Comment: 43 pages, 14 figure
Saturation Physics and Deuteron--Gold Collisions at RHIC
We present a review of parton saturation/Color Glass Condensate physics in
the context of deuteron-gold () collisions at RHIC. Color Glass
Condensate physics is a universal description of all high energy hadronic and
nuclear interactions. It comprises classical (McLerran-Venugopalan model and
Glauber-Mueller rescatterings) and quantum evolution (JIMWLK and BK equations)
effects both in small- hadronic and nuclear wave functions and in the high
energy scattering processes. Proton-nucleus (or ) collisions present a
unique opportunity to study Color Glass Condensate predictions, since many
relevant observables in proton-nucleus collisions are reasonably
well-understood theoretically in the Color Glass Condensate approach. In this
article we review the basics of saturation/Color Glass Condensate physics and
reproduce derivations of many important observables in proton
(deuteron)--nucleus collisions. We compare the predictions of Color Glass
physics to the data generated by experiments at RHIC and observe an
agreement between the data and the theory, indicating that Color Glass
Condensate has probably been discovered at RHIC. We point out further
experimental measurements which need to be carried out to test the discovery.Comment: 113 pages, 65 figures, minor changes, version accepted for
publication in Progress in Particle and Nuclear Physic
Direct and Inverse Computational Methods for Electromagnetic Scattering in Biological Diagnostics
Scattering theory has had a major roll in twentieth century mathematical
physics. Mathematical modeling and algorithms of direct,- and inverse
electromagnetic scattering formulation due to biological tissues are
investigated. The algorithms are used for a model based illustration technique
within the microwave range. A number of methods is given to solve the inverse
electromagnetic scattering problem in which the nonlinear and ill-posed nature
of the problem are acknowledged.Comment: 61 pages, 5 figure
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