57 research outputs found
D-instantons and multiparticle production in N=4 SYM
N=4 Super-symmetric Yang-Mills theory (N=4 SYM) in the strong coupling regime
has been successfully applied (through the AdS/CFT correspondence) to the
description of strongly coupled plasma which is a multiparticle state. Yet, the
high-energy scattering in the strong coupling limit of N=4 SYM is purely
elastic, so this multiparticle final state can never be produced: this is
because in this limit the theory is dual to weak supergravity, and the dominant
interaction is the elastic graviton exchange. Here we propose a resolution of
this dilemma by considering the contribution of D-instantons in bulk
space to the scattering amplitude. We argue that D-instantons coupled to
dilatons and axions are responsible for multiparticle production in strongly
coupled N=4 SYM, and the corresponding cross section increases with energy. We
evaluate the intercept and the slope of the corresponding Pomeron trajectory in
terms of the typical size of the D-instanton, and argue that the resulting
physical picture may resemble the real world.Comment: 22 pp and 11 figures in the eps forma
Gluon saturation effects on J/Psi production in heavy ion collisions
We consider a novel mechanism for J/Psi production in nuclear collisions
arising due to the high density of gluons. We calculate the resulting J/Psi
production cross section as a function of rapidity and centrality. We evaluate
the nuclear modification factor and show that the rapidity distribution of the
produced J/Psi's is significantly more narrow in AA collisions due to the gluon
saturation effects. Our results indicate that gluon saturation in the colliding
nuclei is a significant source of J/Psi suppression that can be disentangled
from the quark-gluon plasma effects.Comment: 5 pages, 3 figures; v2: typos corrected; presentation improve
Hadron multiplicity in pp and AA collisions at LHC from the Color Glass Condensate
We provide quantitative predictions for the rapidity, centrality and energy
dependencies of inclusive charged-hadron productions for the forthcoming LHC
measurements in nucleus-nucleus collisions based on the idea of gluon
saturation in the color-glass condensate framework. Our formulation gives very
good descriptions of the first data from the LHC for the inclusive
charged-hadron production in proton-proton collisions, the deep inelastic
scattering at HERA at small Bjorken-x, and the hadron multiplicities in
nucleus-nucleus collisions at RHIC.Comment: 7 pages, 8 figures; v3: minor changes, one reference added, results
unchanged, the version to appear in Phys. Rev.
The onset of classical QCD dynamics in relativistic heavy ion collisions
The experimental results on hadron production obtained recently at RHIC offer
a new prospective on the energy dependence of the nuclear collision dynamics.
In particular, it is possible that parton saturation -- the phenomenon likely
providing initial conditions for the multi--particle production at RHIC
energies -- may have started to set in central heavy ion collisions already
around the highest SPS energy. We examine this scenario, and make predictions
based on high density QCD for the forthcoming 22 GeV run at RHIC.Comment: 4 pages, 2 figures, revte
Production of q bar-q Pairs in Proton-Nucleus Collisions at High Energies
We calculate production of quark-antiquark pairs in high energy
proton-nucleus collisions both in the quasi-classical approximation of
McLerran-Venugopalan model and including quantum small- evolution. The
resulting production cross section is explicitly expressed in terms of
Glauber-Mueller multiple rescatterings in the classical case and in terms of
dipole-nucleus scattering amplitude in the quantum evolution case. We
generalize the result of one of us (K.T.) beyond the aligned jet
configurations. We expand on the earlier results of Blaizot, Gelis and
Venugopalan by deriving quark production cross section including quantum
evolution corrections in rapidity intervals both between the quarks and the
target and between the quarks and the projectile.Comment: 18 pages, 3 figures; typos corrected, discussion extende
Classical gluodynamics in curved space--time and the soft Pomeron
QCD at the classical level possesses scale invariance which is broken by
quantum effects. This ``dimensional transmutation'' phenomenon can be
mathematically described by formulating classical gluodynamics in a curved,
conformally flat, space-time with non-vanishing cosmological constant. We study
QCD high-energy scattering in this theory. We find that the properties of the
scattering amplitude at small momentum transfer are determined by the energy
density of vacuum fluctuations. The approach gives rise to the power growth of
the total hadron-hadron cross section with energy, i.e. the Pomeron. The
intercept of the Pomeron and the multiplicity of produced particles are
evaluated. We also speculate about a possible link between conformal anomaly
and TeV scale quantum gravity.Comment: 13 pages, 4 figure
Chemical composition of the decaying glasma
The the initial stage of a relativistic heavy ion collision can be described
by a classical color field configuration known as the Glasma. The production of
quark pairs from this background field is then computed nonperturbatively by
numerically solving the Dirac equation in the classical background. The result
seems to point towards an early chemical equilibration of the plasma.Comment: 8 pages, 5 figures, invited talk at Stangeness in Quark Matter 2006
(SQM06), UCLA, March 200
Color mixing in high-energy hadron collisions
The color mixing of mesons propagating in a nucleus is studied with the help
of a color-octet Pomeron partner present in the two-gluon model of the Pomeron.
For a simple model with four meson-nucleon channels, color mixings are found to
be absent for pointlike mesons and very small for small mesons. These results
seem to validate the absorption model with two independent color components
used in recent analyses of the nuclear absorption of mesons produced
in nuclear reactions.Comment: 3 journal-style page
Recent Heavy-Flavor results at STAR
We present the recent results on non-photonic electron (NPE) yields from RHIC
run8 p+p collisions. The ratio as a function of in run8 with a
factor of 10 reduction of the inner detector material at STAR is found to be
consistent with those results from run3 taking into account the NPE from charm
leptonic decay and the difference of photonic electron yield from photon
conversion in detector material. \Jpsi spectra in \pp and \cucu collisions at
\sNN = 200 GeV with high sampled luminosity \Jpsi spectrum at high-\pT follows
scaling, but the scaling is violated at low \pT. -hadron
correlations in \pp collisions are studied to understand the \Jpsi production
mechanism at high . We observed an absence of charged hadrons accompanying
\Jpsi on the near-side, in contrast to the strong correlation peak in the
di-hadron correlations. This constrains the -meson contribution and jet
fragmentation to inclusive \Jpsi to be . Yields in
minimum-bias \cucu collisions are consistent with those in \pp collisions
scaled by the underlying binary nucleon-nucleon collisions in the measured \pT
range. Other measurements and future projects related to heavy-flavors are
discussed.Comment: 8 pages 4 figures, proceedings of the International Conference on
Strangeness in Quark Matter 2008 - Beijing, China, Oct. 6-10, 200
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