Bose-Einstein correlations of three charged pions in hadronic Z$^{\bf 0}$ decays

The OPAL Collaboration:     K. Ackerstaff - et al.

doi:doi:10.1007/s100529800970

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2018 Impact factor 4.843

Particles and Fields

Eur. Phys. J. C 5, 239-248
DOI 10.1007/s100529800970

Bose-Einstein correlations of three charged pions
in hadronic Z $^{\bf 0}$ decays

The OPAL Collaboration
K.Ackerstaff $^{\rm 8}$ - et al.

⁸ CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland

Received: 7 May 1998 / Published online: 12 August 1998

Abstract
Bose-Einstein Correlations (BEC) of three identical charged pions were studied in $4 \times 10^6$ hadronic ${\rm Z}^0$ 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 $r_3 = 0.580 \pm 0.004 \mbox{~(stat.)}\pm 0.029 \mbox{~(syst.)}\mbox{~fm}$ and a strength of $\lambda_3 = 0.504 \pm 0.010 \mbox{~(stat.)}\pm 0.041 \mbox{~(syst.)}$ . The Coulomb correction was found to increase the $\lambda_3$ value by $\sim 9\%$ and to reduce r₃ by $\sim 6\%$ . The measured $\lambda_3$ corresponds to a value of $0.707 \pm 0.014 \mbox{~(stat.)}\pm 0.078 \mbox{~(syst.)}$ when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed.