Morphology of high-multiplicity events in heavy ion collisions

Abstract

We discuss opportunities that may arise from subjecting high-multiplicity events in relativistic heavy ion collisions to an analysis similar to the one used in cosmology for the study of fluctuations of the cosmic microwave background (CMB). To this end, we discuss examples of how pertinent features of heavy ion collisions including global characteristics, signatures of collective flow, and event-wise fluctuations are visually represented in a Mollweide projection commonly used in CMB analysis, and how they are statistically analyzed in an expansion over spherical harmonic functions. If applied to the characterization of purely azimuthal dependent phenomena such as collective flow, the expansion coefficients of spherical harmonics are seen to contain redundancies compared to the set of harmonic flow coefficients commonly used in heavy ion collisions. Our exploratory study indicates, however, that these redundancies may offer novel opportunities for a detailed characterization of those event-wise fluctuations that remain after subtraction of the dominant collective flow signatures. By construction, the proposed approach allows also for the characterization of more complex collective phenomena like higher-order flow and other sources of fluctuations, and it may be extended to the characterization of phenomena of noncollective origin such as jets.

Introductory Overview of Quark Matter 2012

“…It is for instance validated by the recent successes of the Cosmic Microwave Background Cosmology that allowed to determine the material composition of our Universe with a few percent uncertainties from a fluctuation analysis in terms of multipole moments. The analogies between these CMB fluctuation analyses and the analyses of heavy ion collisions are indeed striking, and have been pointed out repeatedly [33,34,35]. Here, I do not want to run through all aspects of this analogy.…”

Studying Heavy Ion Collisions Using Methods From Cosmic Microwave Background (CMB) Analysis

“…The present exposition is a much condensed account of ref. [10]. to which we refer the reader for full details.…”

“…In ref. [10] we describe a systematic analysis of simulated events with flow of various magnitudes (and orders) and varying symmetry plane angle. We also establish relationships between the b lm and the v n and φ n coefficients.…”

“…A main message of this talk is, apart from drawing attention to the method outlined in ref. [10], [11] to point out that the experimental conditions at the LHC at CERN combined with powerful experiments such as ALICE [9] will, in the near future make it possible to collect very significant statistics for each event in f.ex. Pb+Pb collisions.…”

Nonlinear evolution of density and flow perturbations on a Bjorken background

“…It has been noted repeatedly [1][2][3] that the collective dynamics of the hot and dense QCD matter produced in ultrarelativistic heavy-ion collisions shares many commonalities with the expansion dynamics of the early Universe. Both systems are initially relativistic, of high energy density and rapidly expanding.…”