In-medium minijet dissipation in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 and 200 GeV studied with charge-independent two-particle number fluctuations and correlations

Abstract

Medium effects on charged-particle production are studied using three analysis techniques. We find angular collinearity and number correlations on $p_t$ at moderate $p_t<3$ GeV/$c$. In this $p_t$ range abundant multiplicities enable precision measurements of correlations of non-identified hadrons for kinematic variables ($p_t$,$η$,$ϕ$). Methods include (1) direct construction of two-particle correlation functions, (2) inversion of the bin-size dependence of non-statistical multiplicity fluctuations and (3) two-dimensional discrete wavelet analysis. Two-particle correlations on $p_t$ exceed expectations from a model of equilibrated events with fluctuating global temperature. A correlation excess at higher $p_t$ is interpreted as final-state remnants of initial-state semi-hard collisions. Lower-$p_t$ correlations exhibit a saddle structure varying with centrality. Variations in the forms and strengths of low and high $p_t$ correlations with centrality suggest transport of semi-hard collision products into the lower $p_t$ region as a manifestation of in-medium dissipation of minijets. Correlations on $p_t$ can be associated with angular correlations on ($η$,$ϕ$), using analysis methods (1), (2) or (3). In particular, wavelet analysis (3) is performed in the ($η$,$ϕ$) space in bins of $p_t$ ($<2$ GeV/$c$). Observed angular correlation structures include those attributed to quantum correlations and elliptic flow, as well as a localized structure, increasing in amplitude with $p_t$, and presumed to originate with minijets. That structure evolves with increasing centrality in a way which also suggests dissipation, including an increased correlation length on $η$ which may be related to the influence of a longitudinally expanding medium on minijet fragmentation.