George Moschelli

Long range correlations and the soft ridge in relativistic nuclear collisions

Relativistic Heavy Ion Collider experiments exhibit correlations peaked in relative azimuthal angle and extended in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the untriggered ridge arises when particles formed by flux tubes in an early Glasma stage later manifest transverse flow. Combining a blast wave model of flow fixed by single-particle spectra with a simple description of the Glasma, we find excellent agreement with current data.

Fluctuation Probes of Early-Time Correlations in Nuclear Collisions

a) Department of Physics and Astronomy, Wayne State University, 666 W Hancock, Detroit, MI, 48202, USAb) Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University,Ruth-Moufang-Str. 1, 60438 Frankfurt am Main, Germany(Dated: July 26, 2011)Correlation measurements imply that anisotropic ow in nuclear collisions includes a novel tri-angular component along with the more familiar elliptic-ow contribution. Triangular ow hasbeen attributed to event-wise uctuations in the initial shape of the collision volume. We ask twoquestions: 1) How do these shape uctuations impact other event-by-event observables? 2) Canwe disentangle fundamental information on the early time uctuations from the complex ow thatresults? We study correlation and uctuation observables in a framework in which ux tubes inan early Glasma stage later produce hydrodynamic ow. Calculated multiplicity and transversemomentum uctuations are in excellent agreement with data from 62.4 GeV Au+Au up to 2.76TeV Pb+Pb.

Soft contribution to the hard ridge in relativistic nuclear collisions

Nuclear collisions exhibit near side long-range rapidity correlations not present in proton–proton collisions. Because the correlation structure is wide in relative pseudorapidity and narrow in relative azimuthal angle, it is known as the ridge. Similar ridge structures are observed in correlations of particles associated with a jet trigger (the hard ridge) as well as correlations without a trigger (the soft ridge). Earlier we argued that the soft ridge arises when particles formed in an early Glasma stage later manifest transverse flow. We extend this study to address new soft ridge measurements. We then determine the contribution of flow to the hard ridge.

Viscosity and the soft ridge at RHIC

Correlation studies exhibit a ridge-like feature in rapidity and azimuthal angle, with and without a jet trigger. We ask whether this feature in untriggered correlations can be a consequence of transverse flow and viscous diffusion.

Boltzmann-Langevin Approach to Pre-equilibrium Correlations in Nuclear Collisions

Correlations born before the onset of hydrodynamic flow can leave observable traces on the final state particles. Measurement of these correlations can yield important information on the isotropization and thermalization process. Starting from a Boltzmann-like kinetic theory in the presence of dynamic Langevin noise, we derive a new partial differential equation for the two-particle correlation function that respects the microscopic conservation laws. We illustrate how this equation can be used to study the effect of thermalization on long range correlations.

Two Ridges, One Explanation

Abstract We attribute the phenomenon known as “the ridge” to long range initial state correlations from Color Glass Condensate flux tubes and later stage radial flow. We show that this description can explain the amplitude and azimuthal width of the soft ridge and nearly explain that of the hard ridge, suggesting that the two are essentially the same phenomenon.