413 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
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
Baryon Stopping in Proton-Nucleus Collisions
We calculate the inclusive small-x valence quark production cross section in
proton-nucleus collisions at high energies. The calculation is performed in the
framework of the Color Glass Condensate formalism. We consider both the case
when the valence quark originates inside the nucleus and the case when it
originates inside the proton. We first calculate the cross section in the
quasi-classical approximation resumming the multiple rescatterings with the
nucleus. Then we include the the effects of double logarithmic reggeon
evolution and leading logarithmic gluon evolution in the obtained cross
section. The calculated nuclear modification factor for the stopped baryons
exhibits Cronin enhancement in the quasi-classical approximation and
suppression at high energies/rapidities when quantum evolution corrections are
included, providing a new observable which can be used to test Color Glass
physics.Comment: 30 pages, 12 figures One figure and comments added. Version to appear
in Nucl. Phys.
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
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
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
Prompt photons at RHIC
We calculate the inclusive cross section for prompt photon production in
heavy-ion collisions at RHIC energies ( GeV and
GeV) in the central rapidity region including next-to-leading order,
, radiative corrections, initial state nuclear
shadowing and parton energy loss effects. We show that there is a significant
suppression of the nuclear cross section, up to at
GeV, due to shadowing and medium induced parton energy loss effects. We find
that the next-to-leading order contributions are large and have a strong
dependence.Comment: 9 pages, 5 figures, expanded discussion of the K facto
The initial energy density of gluons produced in very high energy nuclear collisions
In very high energy nuclear collisions, the initial energy of produced gluons
per unit area per unit rapidity, , is equal to , where is proportional to the gluon density per unit
area of the colliding nuclei. For an SU(2) gauge theory, we perform a
non--perturbative numerical computation of the function . It
decreases rapidly for small but varies only by %, from
to , for a wide range 35.36--296.98 in , including the range relevant for collisions at RHIC and LHC. Extrapolating
to SU(3), we estimate the initial energy per unit rapidity for Au-Au collisions
in the central region at RHIC and LHC.Comment: 11 pages, Latex, 3 figures; revised version-includes additional
numerical data; reference adde
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