Long-range near-side correlation in $e^+e^-$ Collisions at 183-209 GeV with ALEPH Archived Data

TL;DR

This paper reports the first measurement of two-particle angular correlations in high-energy $e^+e^-$ collisions, revealing a long-range near-side excess not predicted by simulations, and introduces harmonic anisotropy coefficients in such collisions.

Contribution

It provides the first measurement of harmonic anisotropy coefficients in $e^+e^-$ collisions and observes a long-range correlation structure at high multiplicities.

Findings

Observation of long-range near-side excess in high-multiplicity events.

First measurement of harmonic anisotropy coefficients $v_n$ in $e^+e^-$ data.

Discrepancy between observed correlations and Monte Carlo predictions.

Abstract

The first measurement of two-particle angular correlations for charged particles with LEP-II data is presented. The study is performed using archived hadronic $e^+e^-$ data collected by ALEPH at center-of-mass energies up to 209 GeV, above the $W^+W^-$ production threshold, which provide access to unprecedented charged-particle multiplicities and more complex color-string configurations if compared to previous measurements at LEP-I energies. An intriguing long-range near-side excess is observed in the correlation function measured with respect to the thrust axis in the highest multiplicity interval $N_{\mathrm{trk}}\geq 50$. Such a structure is not predicted by the Monte-Carlo simulation. The harmonic anisotropy coefficients $v_n$, which result from the Fourier expansion of the two-particle correlation functions, were also measured for the first time in $e^+e^-$ data, and compared to PYTHIA6 predictions and to the results obtained in proton-proton collisions. The results presented in the Letter provide novel experimental constraints on the formation of collective phenomena in point-like $e^+e^-$ collisions.