579 research outputs found
Production of Forward Rapidity Photons in High Energy Heavy Ion Collisions
We consider production of prompt photons in high energy gold-gold and
deuteron-gold collisions in the forward rapidity region of RHIC ().
In this kinematics, the projectile partons typically have large while
the target partons are mostly at very small so that the primary
partonic collisions involve valence quarks from the projectile and gluons from
the target. We take the target nucleus to be a Color Glass Condensate while the
projectile deuteron or nucleus is treated as a dilute system of partons. We
show that the photon production cross section can be written as a convolution
of a quark-nucleus scattering cross section, involving a quark anti-quark
dipole, with the Leading Order quark-photon fragmentation function. We consider
different models of the quark anti-quark dipole and show that measurement of
photons in the forward rapidity region at RHIC can distinguish between
different parameterizations of the dipole cross section as well as help clarify
the role of parton coalescence models in hadron production at RHIC.Comment: 9 pages, 4 figure
Non-global jet evolution at finite N_c
Resummations of soft gluon emissions play an important role in many
applications of QCD, among them jet observables and small x saturation effects.
Banfi, Marchesini, and Smye have derived an evolution equation for non-global
jet observables that exhibits a remarkable analogy with the BK equation used in
the small x context. Here, this analogy is used to generalize the former beyond
the leading N_c approximation. The result shows striking analogy with the
JIMWLK equation describing the small x evolution of the color glass condensate.
A Langevin description allows numerical implementation and provides clues for
the formulation of closed forms for amplitudes at finite N_c. The proof of the
new equation is based on these amplitudes with ordered soft emission. It is
fully independent of the derivation of the JIMWLK equation and thus sheds new
light also on this topic.Comment: 22 page
Rapidity dependence of the photon to pion production ratio in high energy collisions
We investigate rapidity dependence of the ratio of photon and pion production
cross sections in high energy proton (deuteron) - nucleus collisions at RHIC
and LHC. This ratio, and its rapidity dependence can be a sensitive probe of
high density QCD (Color Glass Condensate) dynamics and shed further light on
the role of saturation physics at RHIC and LHC.Comment: 8 pages, 3 figure
Two-hadron correlations in the Color Glass Condensate formalism
Two-hadron correlations are a sensitive probe of the dynamics of gluon
saturation and the Color Glass Condensate formalism where the degrees of
freedom are Wilson lines of the gluon field. It is shown that unlike structure
functions in DIS and single hadron production in proton-nucleus collisions,
higher point functions of Wilson lines appear in two-hadron production cross
section. We derive equations for the energy () evolution of these higher
point functions using the JIMWLK Hamiltonian and show that dipole
approximation, employed in the literature to fit the di-hadron data measured by
the STAR collaboration in the forward rapidity region, breaks down. This
necessitates an investigation of the full hierarchy of the JIMWLK evolution
equations for these higher point functions and their solutions. This can then
be used to make a quantitative analysis of the di-hadron correlations in the
forward rapidity region in deuteron-gold collisions at RHIC and in the long
range rapidity correlations observed in proton-proton collisions at the LHC.Comment: 10 pages, based on talks given by the author in in the program "High
Energy Strong Interactions 2010" at the Yukawa Institute for Theoretical
Physics, July-August 2010, Kyoto, Japan and in the "5th International
Workshop on high Physics at LHC 2010", September - October, 2010,
Mexico City, Mexic
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