Measurements of Two-Particle Correlations in e^{+}e^{-} Collisions at 91GeV with ALEPH Archived Data.

Anthony Badea,Michael Peters,Paoti Chang,Gian Michele Innocenti,Jesse Thaler,Marcello Maggi,Austin Baty,Tzu-An Sheng,Christopher Mcginn,Yen-Jie Lee

doi:10.1103/physrevlett.123.212002

Abstract

Measurements of two-particle angular correlations of charged particles emitted in hadronic Z decays are presented. The archived e^{+}e^{-} annihilation data at a center-of-mass energy of 91GeV were collected with the ALEPH detector at LEP between 1992 and 1995. The correlation functions are measured over a broad range of pseudorapidity and full azimuth as a function of charged particle multiplicity. No significant long-range correlation is observed in either the lab coordinate analysis or the thrust coordinate analysis, where the latter is sensitive to a medium expanding transverse to the color string between the outgoing qq[over ¯] pair from Z boson decays. The associated yield distributions in both analyses are in better agreement with the prediction from the pythia v6.1 event generator than from herwig v7.1.5. They provide new insights to showering and hadronization modeling. These results serve as an important reference to the observed long-range correlation in proton-proton, proton-nucleus, and nucleus-nucleus collisions.

Highlights

Measurements of two-particle angular correlation functions in high multiplicity proton-proton, protonnucleus, and nucleus-nucleus (AA) collisions have revealed a ridgelike structure for particle pairs having large differences in pseudorapidity [Δη, where η 1⁄4 − ln tan ðθ=2Þ and the polar angle θ is defined relative to the counterclockwise beam], but small differences in azimuthal angle (Δφ) [1,2,3,4,5,6,7,8]
Measurements of two-particle angular correlations of charged particles emitted in hadronic Z decays are presented
The correlation functions are measured over a broad range of pseudorapidity and full azimuth as a function of charged particle multiplicity

Summary

Published by the American Physical Society

[19] and are required to have a transverse momentum with respect to the beam axis (plTab) above 0.2 GeV=c and j cos θlabj < 0.94 in the lab frame. To study the event multiplicity dependence of the correlation function, the analysis is performed with events in 5 multiplicity intervals classified by the number of reconstructed charged particle tracks (Ntrk) with plTab > 0.2 GeV=c. For the purposes of calculating the thrust direction, an extra particle corresponding to the unreconstructed momentum of the event is included This reduces the effects of detector inefficiencies on the final correlation function. The variation of the thrust axis direction causes the ALEPH detector acceptance in the thrust coordinates to vary on an event-by-event basis This is accounted for by recalculating the kinematics for particles in paired events with respect to the thrust axis in the signal event. (3.4%) is quoted for the lab (thrust) coordinate analysis

Thrust coordinates

Findings

ALEPH Archived Data