Bose-Einstein Correlations of Three Charged Pions in Hadronic Z^0 Decays
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Bose-Einstein Correlations (BEC) of three identical charged pions were studied in 4 x 10^6 hadronic Z^0 decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of r_3 = 0.580 +/- 0.004 (stat.) +/- 0.029 (syst.) fm and a strength of λ_3 = 0.504 +/- 0.010 (stat.) +/- 0.041 (syst.). The Coulomb correction was found to increase the λ_3 value by \~9% and to reduce r_3 by ~6%. The measured λ_3 corresponds to a value of 0.707 +/- 0.014 (stat.) +/- 0.078 (syst.) when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed.
19 pages, LaTeX, 5 eps figures included, accepted by Eur. Phys. J. C
19 pages, LaTeX, 5 eps figures included, accepted by Eur. Phys. J. C