Gluon spectrum in the glasma from JIMWLK evolution

The JIMWLK equation with a "daughter dipole" running coupling is solved numerically starting from an initial condition given by the McLerran-Venugopalan model. The resulting Wilson line configurations are then used to compute the spectrum of gluons comprising the glasma inital state of a high energy heavy ion collision. The development of a geometrical scaling region makes the spectrum of produced gluons harder. Thus the ratio of the mean gluon transverse momentum to the saturation scale grows with energy. Also the total gluon multiplicity increases with energy slightly faster than the saturation scale squared.Comment: 7 pages, 8 figures, RevTeX. V2: typo corrections, corrected fig 1. Published in PL

Multiplicity distributions and long range rapidity correlations

The physics of the initial conditions of heavy ion collisions is dominated by the nonlinear gluonic interactions of QCD. These lead to the concepts of parton saturation and the Color Glass Condensate (CGC). We discuss recent progress in calculating multi-gluon correlations in this framework, prompted by the observation that these correlations are in fact easier to compute in a dense system (nucleus-nucleus) than a dilute one (proton-proton).Comment: 7 pages, 4 figures, talk at "Saturation, the CGC and the Glasma: What have we learned from RHIC?" RBRC workshop, May 201

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

On the running coupling in the JIMWLK equation

We propose a new method to implement the running coupling constant in the JIMWLK equation, imposing the scale dependence on the correlation function of the random noise in the Langevin formulation. We interpret this scale choice as the transverse momentum of the emitted gluon in one step of the evolution and show that it is related to the "Balitsky" prescription for the BK equation. This slows down the evolution speed of a practical solution of the JIMWLK equation, bringing it closer to the x-dependence inferred from fits to HERA data. We further study our proposal by a numerical comparison of the BK and JIMWLK equations.Comment: 13 pages, 11 figures, RevTe

J/Psi production in ultraperipheral Pb+Pb and p+Pb collisions at energies available at the CERN Large Hadron Collider

We compute cross sections for incoherent and coherent diffractive J/Psi production in ultraperipheral nucleus-nucleus and proton-nucleus collisions using two different dipole models fitted to HERA data. We obtain a reasonably good description of the available ALICE data for coherent J/\Psi production and present our prediction for the incoherent cross section. We also find that while the normalization of the cross section depends quite strongly on the dipole model and vector meson wave function used, the rapidity dependence is very well constrained.Comment: 6 pages, 5 figures. RevTeX. v2: references added, corrected a numerical error (small effect on coherent cross section), conclusions unchanged. v3: references updated, published in Phys. Rev.