Multi-particle Integral and Differential Correlation Functions

Abstract

This paper formalizes the use of integral and differential cumulants for measurements of multi-particle event-by-event transverse momentum fluctuations, rapidity fluctuations, as well as net charge fluctuations. This enables the introduction of multi-particle balance functions, defined based on differential correlation functions (factorial cumulants), that suppress two and three prong resonance decays effects and enable measurements of underlying long range correlations obeying quantum number conservation constraints. These multi-particle balance functions satisfy simple sum rules determined by quantum number conservation. It is additionally shown that these multi-particle balance functions arise as an intrinsic component of high-order net charge cumulants. This implies that the magnitude of these cumulants, measured in a specific experimental acceptance, is strictly constrained by charge conservation and primarily determined by the rapidity and momentum width of these balance functions. The paper also presents techniques to reduce the computation time of differential correlation functions up to order $n=$10 based on the methods of moments.