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 Lithium Fluoride (LiF) crystal radiators and MWPCs filled with a CH4/TEA gas mixture. Part of the radiator crystals will have the new 'sawtooth' geometry. We have tested the first two of the 30 detector modules together with the first 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. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

A measurement of the spin alignment of charged D* mesons produced in continuum e⁺e^-→cc̄ events at √s = 10.5 GeV is presented. This study using 4.72 fb^-1 of CLEO II data shows that there is little evidence of any D* spin alignment.

Abstract:

Using a 73.6 pb^-1 data sample of Y(2S) events collected with the CLEO II detector at the Cornell Electron Storage Ring, we have investigated the hadronic transitions between the Y(2S) and the Y(1S). The dipion transition Y(2S)→Y(1S)π⁺π was studied using two different analysis techniques. Selecting events in which Y(1S)→e⁺e^-,μ⁺μ^- ("exclusive" analysis), and using the Y(1S) leptonic branching fractions world averages from the PDG review, we obtained B(Y(2S)→Y(1S)π⁺π^-) = 0.189±0.004±0.010, while using a method allowing Y(1S)→anything ("inclusive" analysis) we obtained B(Y(2S)→Y(1S)π⁺π^- = 0.196 ±0.002±0.010. The appropriate weighted average of the two measurements gives B(Y(2S) →Y(1S)μ⁺μ^-) = 0.192±0.002±0.010. Combining the exclusive and inclusive results we derive the Y(1S) leptonic branching fractions Bee = 0.0229±0.0008±0.0011 and Bμμ = 0.0249±0.0008±0.0013. We also studied Y(2S)→Y(1S)π⁰π⁰ and obtained B(Y(2S)→Y(1S)π⁰π⁰) = 0.092±0.006±0.008. Parameters of the ππ system (dipion invariant mass spectra, angular distributions) were analyzed and found to be consistent with current theoretical models. Lastly, we searched for the η and single π⁰ transitions and obtained the 90% confidence level upper limits B(Y(2S)→Y(1S)η)<0.0028 and B(Y(2S)→Y(1S)π⁰)<0.0011.