Balance functions of (un)identified hadrons in Pb--Pb, p--Pb, and pp collisions at the LHC

Abstract

In ultrarelativistic heavy-ion collisions, correlations of particles with opposite quantum numbers provide insight into quark production mechanisms and time scales, collective motion, and re-scattering in the hadronic phase. The longitudinal and azimuthal widths of balance functions for charged kaons and charged pions are used to examine the two-wave quark production model proposed to explain quark-antiquark production within the QGP, which predicts a large increase in up and down quark pairs relative to strange quark pairs around the time of hadronization. Balance functions are also analyzed in small collision systems such as p--Pb and pp to study fragmentation effects and possible collective effects in high-multiplicity events. A comprehensive set of balance functions has been measured using the ALICE detector, including results for unidentified hadrons in Pb--Pb and p--Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV, for charged pions in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV, p--Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV and pp collisions at $\sqrt{s}=7$ TeV, and for charged kaons in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV. The first balance function yield results are also presented.