Methods for the study of transverse momentum differential correlations

Abstract

We introduce and compare three differential correlation functions for the study of transverse-momentum correlations in p+p and A+A collisions. These consist of inclusive and eventwise and a differential version of the correlation measure C-tildeintroduced by Gavin for experimental study of the viscosity per unit entropy of the matter produced in A+A collisions. We study the quantitative difference between the three observables on the basis of PYTHIA simulations of p+p collisions and A+A collisions consisting of an arbitrary superposition of p+p collision events at {radical}(s)=200 GeV. We observe that inclusive and eventwise correlation functions are remarkably similar to each other whereas the observable C-tilde differs quantitatively from the two. We study the robustness and efficiency dependencies of these observables based on truncated Taylor expansions in efficiency in p+p collisions and on the basis of Monte Carlo simulation using an ad hoc detector efficiency parametrization. We find that all the three observables are essentially independent of detector efficiency. We additionally study the scaling of the correlation measures and find all the observables exhibit an approximate 1/N dependence of the number of participants (N) in A+A collisions. Finally, we study the impact of flowlike anisotropy on the inclusive correlation function and find flowmore » imparts azimuthal modulations similar to those observed with two-particle densities.« less