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

Abstract

A measurement of charged hadron pair correlations in two-dimensional $\hat{I}”\hat{I}\cdot \hat{I}”\ddot{I}•$ 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 19$A$, 30$A$, 40$A$, 75$A$, and 150$A$ GeV/$c$. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The $C(\hat{I}”\hat{I}\cdot ,\hat{I}”\ddot{I}•)$ 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 $(\hat{I}”\hat{I}\cdot ,\hat{I}”\ddot{I}•)=(0,0)$ 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.

28 pages, 17 figures, applied corrections after journal review