400 research outputs found
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
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
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
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
Chiral dynamics and the growth of the nucleon's gluonic transverse size at small x
We study the distribution of gluons in transverse space in the nucleon at
moderately small x (~10^{-2}). At large transverse distances (impact
parameters) the gluon density is generated by the 'pion cloud' of the nucleon,
and can be calculated in terms of the gluon density in the pion. We investigate
the large-distance behavior in two different approaches to chiral dynamics: i)
phenomenological soft-pion exchange, ii) the large-N_c picture of the nucleon
as a classical soliton of the pion field, which corresponds to degenerate N and
Delta states. The large-distance contributions from the 'pion cloud' cause a
\~20% increase in the overall transverse size of the nucleon if x drops
significantly below M_pi/M_N. This is in qualitative agreement with the
observed increase of the slope of the t-dependence of the J/psi photoproduction
cross section at HERA compared to fixed-target energies. We argue that the glue
in the pion cloud could be probed directly in hard electroproduction processes
accompanied by 'pion knockout', gamma^* + N -> gamma (or rho, J/psi) + pi + N',
where the transverse momentum of the emitted pion is large while that of the
outgoing nucleon is restricted to values of order M_pi.Comment: 20 pages, revtex4, 10 eps figure
Resolutions of Several Puzzles at Intermediate and Recent Developments in Correlation
Some of the puzzles on hadron production at intermediate found at RHIC
are explained as natural consequences of parton recombination. In that
framework for hadronization the correlation among hadrons produced in jets can
be calculated. Some new results on both near-side and away-side jet structures
are presented.Comment: 5 pages in LaTeX , 0 figures. Talk given at Quark Matter 200
Saturation and Wilson Line Distributions
We introduce a Wilson line distribution function bar{W}_tau(v) to study gluon
saturation at small Feynman x_F, or large tau=ln(1/x_F). This new distribution
can be obtained from the distribution W_tau(alpha) of the Color Glass
Condensate model and the JIMWLK renormalization group equation. bar{W}_tau(v)
is physically more relevant, and mathematically simpler to deal with because of
unitarity of the Wilson line v. A JIMWLK equation is derived for bar{W}_tau(v);
its properties are studied. These properties are used to complete Mueller's
derivation of the JIMWLK equation, though for bar{W}_tau(v) and not
W_tau(alpha). They are used to derive a generalized Balitsky-Kovchegov equation
for higher multipole amplitudes. They are also used to compute the unintegrated
gluon distribution at x_F=0, yielding a completely flat spectrum in transverse
momentum squared k^2, with a known height. This is similar but not identical to
the mean field result at small k^2.Comment: One reference and two short comments added. To appear in Physical
Revies
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