We have measured the reaction e+e− → e+e− at the ϒ Using athe excess of electron pairs over the QED expectation we obtain an electronic branching ratio of Bee = (5.1 ± 3.0) %. Combining this with publishe values of the muonic branching ratio Bμμ we conclude that the ϒ is a narrow state with a total width < 180 keV at 95% C.L.

We have studied the τ→νρ0π decay in data taken with the PLUTO detector at the DORISe+e− storage ring, at CM energies from 4 to 5 GeV. We have found 27 events with the τ→νρ0π decay mode corresponding to a branching ratio ofB=(5.4±1.7)%. The Dalitz plot and theρ0π mass spectrum are analysed for the ρπ partial wave and spin state. Only theρ0πs-wave as produced by the axial vector current gives a good description. Theρ0π mass spectrum is suggestive of anA1 resonance. An upper limit on τ±→vπ±π+π− withoutρ0 formation is given.

The electronic width Γ ee and the muonic branching ratioB μμ =Γ μμ /Γtot of the Γ(9.46) have been measured as Γ ee =(1.33±0.14) andBμμ=(2.2±2.0)%. From these values a lower limit of Γtot<23keV for the total width of the Γ(9.46) is obtained.

The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction.

The polarization of the f0(1270) and ϱ0(770) produced in the J/ψ decays into f0γ and ϱ0π0 are measured in e+e− collisions at 3.1 GeV. A fit to the f0 production and decay angular distributions yields the values A1/A0 = 0.6 ± 0.3 and A2/A0 = 0.3 −1.6+0.6, where Aλ are the f0 helicity amplitudes. These results are in good agreement with the values predicted from a QCD two-gluon-exchange model. In addition an upper limit of 2.3 × 10−4 is obtained for the J/ψ → f′0(1514) γ decay branching ratio which implies Γ(J/ψ → f′γ)/Γ(J/ψ → f0γ) ⩽ 0.12 ± 0.05.

From an analysis of data taken with the detector PLUTO and the DORIS storage rings we have obtained evidence for jet structure in e+e− annihilation with hadrons. Results for mean sphericity, mean thrust, the angular dependence of the jet axis and for 〈pt〉 and 〈p∥〉 with respect to the jet axis are presented. At 9.4 GeV we also discuss the angular dependence of the charged and neutral deposited energy with respect to the jet axis.

Annihilation of e+e− into final states with a single electron has been studied with the PLUTO detector at the DORIS storage ring at CMS energies from 3.6 to 5 GeV. In the sample of 4-prong events without any detected photon we observe 21 events which we assign to the reaction e+e− → τ+τ− → ννe + νϱ0π. We obtain a branching ratio for τ+ → νϱ0π+ of 0.050 ± 0.015 with an overall systematic uncertainty of 30%. The data are consistent with the ϱπ coming from an A1 meson.