Bose-Einstein correlations ine+e−collisions

Four data sets collected with the Mark II detector during its operation at the SPEAR and PEP $e^{+}$ $e^{\mathrm{-}}$ storage rings at SLAC are used to study the Bose-Einstein correlation between pairs and triplets of like-sign charged pions. The data sets represent four different regions of energy available for hadron production: the J/ψ at √s =3.095 GeV, typical hadronic energy of ≊5 GeV in two-photon events, and annihilation in the energy regions √s =4–7 GeV above the J/ψ, and √s =29 GeV. The Bose-Einstein correlation is studied as a function of $Q^2$, the four-momentum difference squared of the pair, and of $Q_3^2$, an analogous quantity defined for triplets. After corrections for Coulomb effects and pion misidentification, pair analyses indicate a nearly full Bose-Einstein enhancement (λ≊1) in the J/ψ and the two-photon data, and about half the maximum value in the two higher-energy data sets. The pair analysis parameter r lies within a band of ±0.1 fm around 0.7 fm and is essentially the same for all four data sets. Pion triplet analyses give consistent results for the triplet parameters ${\lambda }_3$ and $r_3$. In an attempt to investigate the shape of the pion source, we also study the Bose-Einstein correlation in pion pairs using two-dimensional distributions in components of $Q^2$.