A Study Of Decays Of The Tau Lepton With Charged Kaons

Precise studies of the decays of the tau (tau-) lepton have been made possible by the availability of large, low-background tau samples, such as those produced in e+e- collisions at the Z0 resonance at LEP. This thesis describes a study of tau decay modes containing charged kaons, using data collected by the OPAL experiment at LEP. A charged kaon (K-) is a meson composed of a bound state of a strange quark and an up anti-quark, and has a mass of 0.492 GeV/c2. Another example of a meson is the charged pion (pi-), which is composed of a down quark and an up anti-quark, and has a mass of 0.139 GeV/c 2. Charged pions are often produced in tau decays, but decays including charged kaons only occur approximately 5% of the time. One way to experimentally distinguish between the predominant charged pions and the kaons in tau decays is to determine the energy lost by the particle as it traverses a gas and ionises molecules in that gas; the energy lost in this process is a function of the particle mass. The OPAL detector provides precise measurements of the ionisation energy loss of charged particles, and it is primarily this capability that is exploited in this work to study these tau final states and obtain precise measurements of their branching ratios.