Measurement of an Elongation of the Pion Source in Z Decays

TL;DR

This paper measures Bose-Einstein correlations in pion pairs from Z decays, revealing an elongated pion source along the thrust axis with specific size ratios, using three-dimensional analysis at LEP.

Contribution

It provides the first detailed three-dimensional measurement of the pion source shape in Z decays, highlighting elongation along the thrust axis.

Findings

Pion source is elongated along the thrust axis.

Transverse to longitudinal radius ratio is approximately 0.81.

Analysis performed in three dimensions in the center-of-mass system.

Abstract

We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z decays with the L3 detector at LEP. The analysis is performed in three dimensions in the longitudinal center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of $0.81\pm 0.02 ^{+0.03}_{-0.19}$.