|M.Sc Student||Moed Shulamit|
|Subject||A Search for Rare B Decays with the Opal Detector|
|Department||Department of Physics||Supervisors||Professor Emeritus Shlomo Dado|
|Professor Yoram Rozen|
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.