Two-particle correlations in azimuthal angle and pseudorapidity in central ⁷Be + ⁹Be collisions at the CERN Super Proton Synchrotron

Abstract

A measurement of charged hadron pair correlations in two-dimensional Δ ηΔ ϕ space is presented. The analysis is based on total 30 million central Be + Be collisions observed in the NA61/SHINE detector at the CERN SPS for incident beam momenta of 19A, 30A, 40A, 75A, and 150A Ge/c. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The C(Δ η, Δ ϕ) correlation functions were compared with results from a similar analysis on p + p interactions at similar beam momenta per nucleon. General trends of the back-to-back correlations are similar in central Be + Be collisions and p + p interactions, but are suppressed in magnitude due to the increased combinatorial background. Predictions from the Epos and UrQMD models are compared to the measurements. Evolution of an enhancement around (Δ η, Δ ϕ) = (0 , 0) with incident energy is observed in central Be + Be collisions. It is not predicted by both models and almost non-existing in proton–proton collisions at the same momentum per nucleon.