Dijet asymmetry at the Large Hadron Collider

The MARTINI numerical simulation allows for direct comparison of theoretical model calculations and the latest results for dijet asymmetry from the ATLAS and CMS collaborations. In this paper, partons are simulated as undergoing radiative and collisional processes throughout the evolution of central lead-lead collisions at the Large Hadron Collider. Using hydrodynamical background evolution determined by a simulation which fits well with the data on charged particle multiplicities from ALICE and a value of $\alpha_s\approx 0.25-0.3$, the dijet asymmetry is found to be consistent with partonic energy loss in a hot, strongly-interacting medium.Comment: 8 pages, 3 figures. For version 2: ATLAS' latest analysis is included, with some comments and minor changes of wordin

The shape of the proton at high energies

We present first calculations of the fluctuating gluon distribution in a proton as a function of impact parameter and rapidity employing the functional Langevin form of the JIMWLK renormalization group equation. We demonstrate that when including effects of confinement by screening the long range Coulomb field of the color charges, the evolution is unitary. The large-x structure of the proton, characterized by the position of three valence quarks, retains an effect on the proton shape down to very small values of x. We determine the dipole scattering amplitude as a function of impact parameter and dipole size and extract the rapidity evolution of the saturation scale and the proton radius.Comment: 8 pages, 6 figure

Pseudorapidity correlations in heavy ion collisions from viscous fluid dynamics

We demonstrate by explicit calculations in 3+1 dimensional viscous relativistic fluid dynamics how two-particle pseudorapidity correlation functions in heavy ion collisions at the LHC and RHIC depend on the number of particle producing sources and the transport properties of the produced medium. In particular, we present results for the Legendre coefficients of the two-particle pseudorapidity correlation function in Pb+Pb collisions at 2760 GeV and Au+Au collisions at 200 GeV from viscous hydrodynamics with three dimensionally fluctuating initial conditions. Our results suggest that these coefficients provide important constraints on initial state fluctuations and the transport properties of the quark gluon plasma.Comment: 5 pages, 5 figures, Corrected Eq.(8) and all figures to agree with the corrected definition used by ATLAS, conclusions remain unchanged, added reference