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 so
urce is found to be elongated along the thrust axis with a ratio of transve
rse to longitudinal radius of 0.81 +/- 0.02(-0.19)(+0.03). (C) 1999 Publish
ed by Elsevier Science B.V. All rights reserved.