A. Bäcker

Observation of a Narrow Resonance Formed in e+ e- Annihilation at 9.46-GeV

Abstract An experiment using the PLUTO detector has observed the formation of a narrow, high mass, resonance in e+e− annihilations at the DORIS storage ring. The mass is determined to be 9.46±0.01 GeV which is consistent with that of the Upsilon. The gaussian width σ is observed as 8±1 MeV and is equal to the DORIS energy resolution. This suggests that the resonance is a bound state of a new heavy quark-antiquark pair. An electronic width Γee=1.3±0.4 keV was obtained. In standard theoretical models, this favors a quark charge assignment of 1 3 .

The total hadronic cross section for e+e− annihilation between 3.1 and 4.8 GeV center of mass energy

Abstract Using the solenoidal magnetic detector PLUTO, we have measured the total cross section for e+e− annihilation into hadrons. Results are presented for center of mass energies between 3.6 and 4.8 GeV, and in the regions of the J ψ (3.1) and ψ(3.7) resonances. We also present results for the 2 prong cross section in the energy range 3.6 to 4.8 GeV.

Jet analysis of the ϒ(9.46) decay into charged hadrons

Abstract The direct decay into four and more charged particles of the ϒ(9.46) formed in e+e− collisions is analysed for hadron-jet configurations. The results are compared with the expectations of phase space, a q q two-jet model and a QCD three-gluon decay mechanism. Out of these three models, the three-gluon decay describes best the data.

Evidence for heavy leptons from anomalous μe production in e+e− annihilation

Abstract Events of the type e + e − →μ ± +e ∓ + “nothing” have been observed in the magnetic detector PLUTO at the storage ring DORIS at DESY. The data support the hypothesis of the pair production of heavy leptons, and allow to determine decay parameters. Decay rates into muons and electrons are equal within error, and argue for a new lepton number of the heavy lepton.

Observation of associated Kos-electron production in e+e− annihilation

Abstract We have observed K o s production in e + e − annihilation between 3.6 and 4.4 GeV CMS energy. In the 4.0–4.1 GeV range K o s mesons occur correlated with prompt electrons, indicating the formation and weak decay of charmed particle. Within the sensitivity of the experiment, no K o s -electron correlation is seen at 3.6 and around 4.4 GeV.

Determination of the electronic branching ratio of the ϒ(9.46) and an upper limit for its total width

Abstract 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 B ee = (5.1 ± 3.0) %. Combining this with publishe values of the muonic branching ratio B μμ we conclude that the ϒ is a narrow state with a total width

Inclusive Ks0-production in e+e− annihilation at energies of 3.6 to 5.0 GeV

Abstract We have measured the production cross section for K s 0 in e + e − annihilation from 3.6 to 5.0 GeV center of mass energy. A substantial increase of the K s 0 yield is observed around 4 GeV in qualitative agreement with the charm hypothesis.

Measurement of leptonic branching ratios of the Γ(9.46)

The electronic width Γee and the muonic branching ratioBμμ=Γμμ/Γtot of the Γ(9.46) have been measured as Γee=(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.

Measurement of the f0(1270) polarization in the J/ψ → f0 γ decay☆

Abstract The polarization of the f 0 (1270) and ϱ 0 (770) produced in the J/ ψ decays into f 0 γ and ϱ 0 π 0 are measured in e + e − collisions at 3.1 GeV. A fit to the f 0 production and decay angular distributions yields the values A 1 / A 0 = 0.6 ± 0.3 and A 2 / A 0 = 0.3 −1.6 +0.6 , where A λ are the f 0 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 → f 0 γ ) ⩽ 0.12 ± 0.05.

Measurement of the branching ratios for the decays J/ψ(3.1) → fω and J/ψ(3.1) → Bπ

Abstract Decays of the J/ψ (3.1) resonance into final states with four charged and one neutral pion have been investigated. We measured the branching ratios J/ ψ (3.1) → f ω /all = 0.40 ± 0.14)% and J/ ψ (3.1) → (B + π − + B − π + )/all = (0.28 ± 0.07)%.