Georg Viehhauser

Abstract:

The CLEO collaboration is preparing a major upgrade of its present detector including a RICH detector for particle identification. This subdetector system follows the 'proximity focussing' design and uses LiF crystal radiators and MWPCs filled with a CH4/TEA gas mixture as photon detector. Part of the radiator crystals will have the new 'sawtooth' geometry.We have constructed two of the 30 detector modules and tested these together with the first planar and 'sawtooth' radiator crystals in a muon halo beam at Fermilab. For the measurement of the Cherenkov angle we obtain a single photon measurement error of 13.5 mrad for the conventional planar radiator. With 14 detected photons we find a resolution per track of 4.5 mrad. In the first measurement ever of a 'sawtooth' radiator we achieve a resolution of 11.8 mrad for single photons and 4.8 mrad per track for 12.3 detected photons with a reduced geometric acceptance. These results fulfill CLEO III requirements.

Abstract:

We have observed new channels for τ decays with an η in the final state. We study 3-prong tau decays, using the η → γγ and η → 3π0 decay modes and 1-prong decays with two π0’s using the η → γγ channel. The measured branching fractions are B(τ → π−π−π+ηντ = (3.4+0.6-0.5 ± 0.6) × 10-4 and B(τ− → π−2π0ηντ = (1.4 ± 0.6 ± 0.3) × 10-4. We observe clear evidence for f1 → ηππ substructure and measure B(τ− → f1π−ντ) = (5.8+1.4-1.3 ± 1.8) × 10-4. We have also searched for η′(958) production and obtain 90% C.L. upper limits B(τ → π−η′ντ) < 7.4 × 10-5 and B(τ → π−π0η′ντ) < 8.0 × 10-5. © 1997 American Physical Society.

Abstract:

Using 4.8 fb^-1 of data taken with the CLEO II detector, the branching fraction for the Cabibbo suppressed decay D⁺ → π⁰ℓ⁺v measured relative to the Cabibbo favored decay D⁺ → K⁰̄ℓ⁺v is found to be 0.046 ± 0.014 ± 0.017. Using Vcs and Vcd from unitarity constraints, we determine |f^π+(0) / f^K+(0)|² = 0.9 ± 0.3 ± 0.3 We also present a 90% confidence level upper limit for the branching ratio of the decay D⁺ → ηe⁺ve relative to that for D⁺ →⁰e⁺ve of 1.5. © 1997 Published by Elsevier Science B.V.