טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMoed Shulamit
SubjectA Search for Rare B Decays with the Opal Detector
at LEP
DepartmentDepartment of Physics
Supervisors Professor Emeritus Shlomo Dado
Professor Yoram Rozen


Abstract

Rare B meson decays are suggested to give good opportunities for discovering new physics beyond the Standard Model.

A search for the decays   and   was performed using 4.1 million hadronic  events with center-of mass energy of  91GeV collected with the OPAL detector at LEP during the years 1989-1995.

 These decays are strongly suppressed in the Standard Model, but may not be so in models that are extensions of the Standard Model. Therefore these processes provide an appropriate testing ground for physics beyond the Standard Model.

The decay channels that were searched for are induced by the quark transitions   and . These quark transitions are mediated in the Standard Model by box diagrams with the up type quark and the weak bosons inside the loop. 

In the Standard Model the two decay modes have a branching ratio of the order   or less. The expected branching ratios vary between  in models like the Minimal Supersymmetric Standard Model, with and without R-parity conservation, or the two Higgs doublet model.

The search for these decays was done by reconstructing   B meson candidates by combining tracks using different selection criteria based on event variables  measured by the detector and artificial neural network classifications.

In agreement with other searches for these decays done by the CLEO collaboration and the BELLE collaboration, no evidences for a signal are observed and at 90% confidence level an upper limit of   is set on the branching ratio of the decay  and an upper limit of    on the branching  ration of the  decay.