Transverse and longitudinal
in hadronic Z0 decays
The OPAL Collaboration
G.Abbiendi2 - et al.
2 Dipartimento di Fisica dell' Università di Bologna and INFN,
40126 Bologna, Italy
Received: 3 January 2000 / Published online: 8 June 2000 - © Springer-Verlag 2000
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 tside, and longitudinal, rl, 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' = CDATA/CMCfor two-jet events, selected with the Durham algorithm and resolution parameter ycut = 0.04, are r tside = (0.809 0.009 (stat) +0.019-0.032 (syst)) fm, rl = (0.989 0.011 (stat) +0.030-0.015 (syst)) fm and rl/r tside = 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. The results of a unidimensional analysis are also presented.
Copyright Società Italiana di Fisica, Springer-Verlag 2000