853,019 research outputs found
Saturation in nuclei
This talk discusses some recent studies of gluon saturation in nuclei. We
stress the connection between the initial condition in heavy ion collisions and
observables in deep inelastic scattering (DIS). The dominant degree of freedom
in the small x nuclear wavefunction is a nonperturbatively strong classical
gluon field, which determines the initial condition for the glasma fields in
the initial stages of a heavy ion collision. A correlator of Wilson lines from
the same classical fields, known as the dipole cross section, can be used to
compute many inclusive and exclusive observables in DIS.Comment: 7 pages, 3 figures. Talk given at EDS'09: 13th International
Conference on Elastic and Diffractive Scattering, CERN, Geneva, 29th June-3rd
July, 200
Conformal invariant saturation
We show that, in onium-onium scattering at (very) high energy, a transition
to saturation happens due to quantum fluctuations of QCD dipoles. This
transition starts when the order correction of the dipole loop is
compensated by its faster energy evolution, leading to a negative interference
with the tree level amplitude. After a derivation of the the one-loop dipole
contribution using conformal invariance of the elastic 4-gluon amplitude in
high energy QCD, we obtain an exact expression of the saturation line in the
plane (Y,L) where Y is the total rapidity and L, the logarithm of the onium
scale ratio. It shows universal features implying the Balitskyi - Fadin -
Kuraev - Lipatov (BFKL) evolution kernel and the square of the QCD triple
Pomeron vertex. For large L, only the higher BFKL Eigenvalue contributes,
leading to a saturation depending on leading log perturbative QCD
characteristics. For initial onium scales of same order, however, it involves
an unlimited summation over all conformal BFKL Eigenstates. In all cases,
conformal invariance is preserved for the saturation mechanism based on dipole
loops.Comment: 15 pages,3 eps figures; Version to be published in Nucl.Phys.B., one
more figure, writing improvements, results and conclusion unchange
Influence of Mechanical Yielding on Predictions of Saturation: The Saturation Line
It is now well accepted that the mechanical and the water retention behaviour of a soil under unsaturated conditions are coupled and, that such coupling, should be incorporated into a constitutive model for a realistic representation of soil’s response. In existing models, the influence of the mechanical behaviour on the water retention is often represented by a shift of the main wetting retention curve to higher values of matric suction (the difference between pore air and pore water pressures) when the specific volume decreases. This means that any variation of total volumetric strains of compression (whether these are elastic or elasto-plastic) will result in a shift of the main wetting and drying curves to the right, when these curves are represented in the water retention plane. This shift of the main water retention curves, however, should not only influence the unsaturated stress states as often described in the literature, it should also have some impact on the saturated stress states and, more specifically, on the predictions of de-saturation (air-entry point) and saturation (air-exclusion point). From a modelling point of view, it is advantageous to represent this influence through the plastic component of volumetric strain of compression only because, in this way, a consistent representation of the mechanical behaviour for both unsaturated and saturated states can be naturally achieved. This and other advantages resulting from this singular approach are demonstrated in the paper in the context of the Glasgow Coupled Model (GCM)
Colour Dipoles and Saturation
We employ values of the colour dipole cross section extracted from
electroproduction and photoproduction data to show that gluon saturation
effects are not required by the current HERA data but will become important in
the THERA energy region.Comment: 3 pages, 2 figures. Talk given by G.S. at DIS 2000(Liverpool, April
2000
Saturation 2005 (mini-review)
This talk was given at DIS'05 (Madison, April 27-May 2, 2005). It is a brief
review of ups and downs of high density QCD during the past year.Comment: 4 pages and 1 figur
Saturation and geometrical scaling
We discuss emergence of geometrical scaling as a consequence of the nonlinear
evolution equations of QCD, which generate a new dynamical scale, known as the
saturation momentum: Qs. In the kinematical region where no other energy scales
exist, particle spectra exhibit geometrical scaling (GS), i.e. they depend on
the ratio pT=Qs, and the energy dependence enters solely through the energy
dependence of the saturation momentum. We confront the hypothesis of GS in
different systems with experimental data.Comment: 6 pages, 4 figures, based on talk presented at XLVI International
Symposium on Multiparticle Dynamics, 29 August 2016 to 02 September 2016,
Seogwipo, Jeju Island, South Kore
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