749 research outputs found
Vector potential versus colour charge density in low-x evolution
We reconsider the evolution equations for multigluon correlators derived in
hep-ph/9709432. We show how to derive these equations directly in terms of
vector potentials (or colour field strength) avoiding the introduction of the
concept of colour charge density in the intermediate steps. The two step
procedure of deriving the evolution of the charge density correlators followed
by the solution of classical equations for the vector potentials is shown to be
consistent with direct derivation of evolution for vector potentials. In the
process we correct some computational errors of hep-ph/9709432 and present the
corrected evolution equations which have a somewhat simpler appearance.Comment: 15 pages, 1 figure, changes made referee report, to be published in
Phys. Rev
Saturation physics and angular correlations at RHIC and LHC
We investigate the angular correlation between pions and photons produced in
deuteron-gold collisions at RHIC and proton-lead collisions at LHC using the
Color Glass Condensate formalism and make predictions for the dependence of the
production cross section on the angle between the pion and photon at different
rapidities and transverse momenta. Measuring this dependence would shed further
light on the role of high gluon density and saturation dynamics at RHIC and
LHC.Comment: 2-column EPJ C format, requires svjour.cls and svepj.clo; 4 pages, 4
figure
Probing colored glass via photoproduction
In this paper, we calculate the cross-section for the photoproduction of
quark-antiquark pairs in the peripheral collision of ultra-relativistic nuclei,
by treating the color field of the nuclei within the Color Glass Condensate
model. We find that this cross-section is sensitive to the saturation scale
that characterizes the model. In particular, the transverse momentum
spectrum of the produced pairs could be used to measure the properties of the
color glass condensate.Comment: 25 pages LaTeX document - A reference and some footnotes added
(version to appear in Nucl. Phys. A
Shadowing of gluons in perturbative QCD: A comparison of different models
We investigate the different perturbative QCD-based models for nuclear
shadowing of gluons. We show that in the kinematic region appropriate to RHIC
experiment, all models give similar estimates for the magnitude of gluon
shadowing. At scales relevant to LHC, there is a sizable difference between
predictions of the different models.Comment: 11 pages, 4 figure
Photon production in high energy proton-nucleus collisions
We calculate the photon production cross-section in collisions under the
assumption that the nucleus has reached the saturation regime, while the proton
can be described by the standard parton distribution functions. We show that
due to the strong classical field of the nucleus, bremsstrahlung
diagrams become dominant over the direct photon diagrams. In particular, we
show that jet transverse momentum spectrum and correlations are very
sensitive to gluon saturation effects in the nucleus.Comment: 15 pages, 2 figure
Non-Gaussian Correlations in the McLerran-Venugopalan Model
We argue that the statistical weight function W[rho] appearing in the
McLerran-Venugopalan model of a large nucleus is intrinsically non-Gaussian,
even if we neglect quantum corrections. Based on the picture where the nucleus
of radius R consists of a collection of color-neutral nucleons, each of radius
a<<R, we show that to leading order in alpha_s and a/R only the Gaussian part
of W[rho] enters into the final expression for the gluon number density. Thus,
the existing results in the literature which assume a Gaussian weight remain
valid.Comment: 21 pages with 4 figures (revtex
Production of gluons in the classical field model for heavy ion collisions
The initial stages of relativistic heavy ion collisions are studied
numerically in the framework of a 2+1 dimensional classical Yang-Mills theory.
We calculate the energy and number densities and momentum spectra of the
produced gluons. The model is also applied to non central collisions. The
numerical results are discussed in the light of RHIC measurements of energy and
multiplicity and other theoretical calculations. Some problems of the present
approach are pointed out.Comment: 9 pages, 11 figures, RevTeX; error in eq. (11) corrected, figures
clarified, published in Phys. Rev.
Forward Quark Jets from Protons Shattering the Colored Glass
We consider the single-inclusive minijet cross section in pA at forward
rapidity within the Color Glass Condensate model of high energy collisions. We
show that the nucleus appears black to the incident quarks except for very
large impact parameters. A markedly flatter p_t distribution as compared to QCD
in the dilute perturbative limit is predicted for transverse momenta about the
saturation scale, which could be as large as Q_s^2 ~ 10 GeV^2 for a gold
nucleus boosted to rapidity ~10 (as at the BNL-RHIC).Comment: 9 pages, no figure
Polarized 3 parton production in inclusive DIS at small x
Azimuthal angular correlations between produced hadrons/jets in high energy
collisions are a sensitive probe of the dynamics of QCD at small x. Here we
derive the triple differential cross section for inclusive production of 3
polarized partons in DIS at small x using the spinor helicity formalism. The
target proton or nucleus is described using the Color Glass Condensate (CGC)
formalism. The resulting expressions are used to study azimuthal angular
correlations between produced partons in order to probe the gluon structure of
the target hadron or nucleus. Our analytic expressions can also be used to
calculate the real part of the Next to Leading Order (NLO) corrections to
di-hadron production in DIS by integrating out one of the three final state
partons.Comment: 5 pages, 6 figures; version accepted for publication in Physics
Letters
The Wilson renormalization group for low x physics: towards the high density regime
We continue the study of the effective action for low physics based on a
Wilson renormalization group approach. We express the full nonlinear
renormalization group equation in terms of the average value and the average
fluctuation of extra color charge density generated by integrating out gluons
with intermediate values of . This form clearly exhibits the nature of the
phenomena driving the evolution and should serve as the basis of the analysis
of saturation effects at high gluon density at small .Comment: 14 pages, late
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