C. Milstene

τ Production and decay with the cello detector at petra

Abstract The reaction e + e − → τ + τ − has been studied at centre of mass energies between 14.0 and 46.8 GeV with the CELLO detector at the PETRA e + e − collider. We present results for the cross section σ τ and the charge asymmetry A τ . The results are in good agreement with the standard model. We have also measured the topological decay rates BR 1 , BR 3 and BR 5 for the inclusive decay of the τ lepton into one, three and five charge particles. The results confirm and improve earlier CELLO measurements at other energies. We find for the combined values at all energies BR 1 = (84.9 ± 0.4 ± 0.3)%, BR 3 = (15.0 ± 0.4 ± 0.3)% and BR 5 = (0.16 ± 0.13 ± 0.04)%.

Neutrino counting with the CELLO detector and search for supersymmetric particles

A search for single photons, produced in e+e− collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector at the PETRA storage ring. We report on results from data taken at 35 GeV < √s<46.57 GeV. An upper limit of 8.7 (90% CL) on the number of light neutrino species is set. Combining our result with published results from other e+e− experiments the number of light neutrinos is limited to Nv < 4.6 at 90% CL. We also set lower limits on the masses of supersymmetric particles.

Search for production of charged Higgs particles

Abstract A search has been performed for the production of charged Higgs bosons in e+ e− annihilation at center of mass energies up to 46.8 GeV. From the absence of both hadronic and leptonic decay signatures, we exclude them up to a mass of 19 GeV/c2 independent of the hadronic and leptonic branching ratios.

a2(1320) andπ2(1670) formation in the reactionγγ→π+π−π0

The reactione+e−→e+e−π+π−π0 in the untagged mode has been measured with the CELLO detector at PETRA. The cross section is dominated by exclusivea2(1320) production, whose radiative width is determined to beΓγγ=1.00±0.07(stat.)±0.15(syst.)keV. An angular correlation analysis indicates pure helicity 2 with an upper limit on the helicity 0 contribution of 8.2% (at 95% c.l.). Excitation of the pseudotensor meson π20(1670) is observed for the first time in this reaction. The π2 radiative width and its dependence on interference effects are studied.

Inclusive strange particle production in e + e- annihilation

We present an analysis of strange particle production frome+e− annihilation into multihadronic final states. The experiment was performed with the CELLO detector at the PETRA storage ring at DESY, the data was taken at a centre of mass energy of 35 GeV with an integrated luminosity of 86 pb−1. The particlesKS0,K*± and Λ have been identified by their characteristic decays, and differential cross sections for their production have been obtained. From a comparison ofKS0 andK*± rates the Lund vector meson suppression parameterV/(V+P)S has been determined.

K s 0 Kπ production in tagged and untagged γγ interactions

AbstractWe have searched for resonance production in the reaction γγ→Ks0Kπ. No signal was found for theηc and an upper limit for the radiative with

Measurement of the reaction γγ → ϱ+ϱ− with the CELLO detector

\Gamma _{\gamma \gamma }^{\eta _c }

Estimates of the photon structure function derived from factorization

keV (95% c.l.) is obtained. For the glueball candidate η(1440) (previouslyi) the upper limit