A measurement of the mass of the tau lepton

Citation

Jones, Lawrence Aston (1995) A measurement of the mass of the tau lepton. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6q1r-0m94. https://resolver.caltech.edu/CaltechETD:etd-10102007-090831

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

For a conventional charged lepton l under the Standard Model, the electronic branching ratio [...], lifetime [...], mass [...], the dimensionless weak coupling constant [...] and the W-boson mass [...] are related by [...] up to small radiative and electroweak corrections. This implies the following relationship among the above parameters for the [...] and [...] leptons: [...]. In 1992, world averages for the above quantities yielded [...], implying a 2.4 standard deviation disagreement with lepton universality.

A measurement of the [...] production cross section in the region most sensitive to the [...] mass--a few MeV around threshold--provides the opportunity to measure the r mass with greatly improved precision. This thesis presents such a measurement made using the Beijing Spectrometer at the Beijing Electron Positron Collider.

A search was conducted for threshold assuming a parameterized form for the [...] cross section. After each search point a likelihood was generated using all the information from the search so far. This identified the energy where it would be most efficient to search next. The mass value is obtained from a fit to the energy dependence of the cross section. The measurement is independent of the [...] mass.

A likelihood-driven search was carried out at BES based on [...] events. The data has been re-analysed to take into account the additional decay modes [...] , [...], [...], [...], and [...]. This new analysis yields [...] MeV.

Using contemporary values for [...] and [...] and the result above, the ratio of the weak coupling constants becomes [...], and lepton universality is supported.

Thesis Files