Transverse and Longitudinal Bose Einstein Correlations in hadronic Z0 Decays

TL;DR

This study measures Bose-Einstein correlations in Z0 decays, revealing an elongated pion emission source and providing detailed spatial dimensions, which inform models of particle production.

Contribution

It presents the first detailed measurement of transverse and longitudinal Bose-Einstein correlation dimensions in Z0 decays, highlighting source elongation and comparing results with string fragmentation models.

Findings

The emitting source is elongated along the thrust axis.

Measured correlation radii are approximately 0.65-0.81 fm transversely and 0.99 fm longitudinally.

The ratio of longitudinal to transverse radius is about 1.22.

Abstract

Bose-Einstein correlations in pairs of identical charged pions produced in a sample of 4.3 million Z0 hadronic decays are studied as a function of the three components of the momentum difference, transverse ("out" and "side") and longitudinal with respect to the thrust direction of the event. A significant difference between the transverse, r_t_side, and longitudinal, r_l, dimensions is observed, indicating that the emitting source of identical pions, as observed in the Longitudinally CoMoving System, has an elongated shape. This is observed with a variety of selection techniques. Specifically, the values of the parameters obtained by fitting the extended Goldhaber parametrisation to the correlation function C'= C^{DATA}}/C^{MC} for two-jet events, selected with the Durham algorithm and resolution parameter ycut=0.04, are r_t_out=(0.647+-0.011(stat})+0.022-0.124(syst)) fm, r_t_side=(0.809+-0.009(stat)+0.019-0.032}(syst)) fm, r_l=(0.989+-0.011(stat)+0.030-0.015(syst})) fm and r_l/r_t_side=1.222+-0.027(stat})+0.075-0.012(syst). The results are discussed in the context of a recent model of Bose-Einstein correlations based on string fragmentation.