$K^0_S$ production in $\tau$ decays

From a sample of about 160k Z → τ+τ− candidates collected with the ALEPH detector at LEP between 1991 and 1995, τ lepton decays involving K S → π+π− are studied. The K SK L associated production in τ decays is also investigated. The branching ratios are measured for the inclusive decay B(τ−→K0 SXντ ) = (9.70±0.58±0.62) × 10−3, where X− can be anything, and for the exclusive decays B(τ−→Kπ−ντ ) = (8.55±1.17±0.66) × 10−3, B(τ−→Kπ−π0ντ ) = (2.94±0.73±0.37) × 10−3, B(τ−→KK−ντ ) = (1.58±0.42±0.17) × 10−3, B(τ−→KK−π0ντ ) = (1.52±0.76±0.21) × 10−3. The decay τ−→K0 SK Lπντ is studied for the first time, giving a branching ratio B(τ−→K0 SK Lπντ ) = (1.01±0.23±0.13) × 10−3. The channels τ− → K SK Sπντ , τ− → K SK Sππντ , τ− → K SK Lππντ , τ− → Kπ−π0π0ντ , τ− →K0K−π0π0ντ and τ− →K0h+h−h−ντ are also investigated. In addition, mass spectra in the K Sh and K Sh −π0 final states are analysed to provide information on the intermediate states produced in the decays. The ALEPH Collaboration: K S production in τ decays 31 1 Now at CERN, 1211 Geneva 23, Switzerland 2 Also at CERN, 1211 Geneva 23, Switzerland 3 Also at Dipartimento di Fisica, INFN, Sezione di Catania, Catania, Italy 4 Also Istituto di Fisica Generale, Università di Torino, Torino, Italy 5 Also Istituto di Cosmo-Geofisica del C.N.R., Torino, Italy 6 Supported by the Commission of the European Communities, contract ERBCHBICT941234 7 Supported by CICYT, Spain 8 Supported by the National Science Foundation of China 9 Supported by the Danish Natural Science Research Council 10 Supported by the UK Particle Physics and Astronomy Research Council 11 Supported by the US Department of Energy, grant DE-FG0295-ER40896 12 Permanent address: Kangnung National University, Kangnung, Korea 13 Supported by the US Department of Energy, contract DE-FG05-92ER40742 14 Supported by the US Department of Energy, contract DE-FC05-85ER250000 15 Permanent address: Universitat de Barcelona, 08208 Barcelona, Spain 16 Supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Germany 17 Supported by the Direction des Sciences de la Matière, CEA