Partial correlation analysis in ultra-relativistic nuclear collisions

TL;DR

This paper demonstrates that partial covariance is an effective method for incorporating constraints in data analysis of ultra-relativistic nuclear collisions, helping to isolate initial-state physics from trivial fluctuations.

Contribution

It introduces the use of partial covariance for constraining data analysis in nuclear collisions, separating initial-state effects from final-state fluctuations.

Findings

Effective in analyzing forward-backward multiplicity fluctuations

Separates initial-state physics from statistical fluctuations

Applicable to multiple observables and constraints

Abstract

We show that the method of partial covariance is a very efficient way to introduce constraints (such as the centrality selection) in data analysis in ultra-relativistic nuclear collisions. The technique eliminates spurious event-by-event fluctuations of physical quantities due to fluctuations of control variables. Moreover, in the commonly used superposition approach to particle production the method can be used to impose constraints on the initial sources rather than on the finally produced particles, thus separating out the trivial fluctuations from statistical hadronization or emission from sources and focusing strictly on the initial-state physics. As illustration, we use simulated data from hydrodynamics started on the wounded-quark event-by-event initial conditions, followed with statistical hadronization, to show the practicality of the approach in analyzing the forward-backward multiplicity fluctuations. We mention generalizations to the case with several constraints and other observables, such as the transverse momentum or eccentricity correlations.