Two-particle correlation in e^+e^- collisions at 91-209 GeV with archived ALEPH data

Abstract

We present the first measurement of two-particle angular correlations of charged particles produced in 𝑒 + 𝑒 − annihilation up to √ 𝑠 = 209 GeV. This analysis utilized the archived hadronic 𝑒 + 𝑒 − data at center-of-mass energy between 91 and 209 GeV collected with the ALEPH detector at LEP between 1992 and 2000. The angular correlation functions are measured over a broad range of pseudorapidity and full azimuth as a function of charged particle multiplicity for the first time with LEP-2 data. At 91 GeV, no significant long-range correlation is observed in either the beam coordinate analysis or the thrust coordinate analysis, where the latter is sensitive to a medium expanding transverse to the color string between the outgoing 𝑞 q pair from the Z boson decays. Results with 𝑒 + 𝑒 − data at higher collision energy than 91 GeV, providing higher event multiplicity reach up to around 50, are presented for the first time. The thrust axis analysis shows a longrange near-side excess in the two-particle correlation function. We performed Fourier series decomposition of the two-particle correlation functions. In high multiplicity events with more than 50 particles, the extracted Fourier coefficients 𝑣 2 and 𝑣 3 magnitudes in data are larger than the MC reference.