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UBC Theses and Dissertations

Evaluation of the photonic conversion finder for the BABAR experiment Lurie, Zerah

Abstract

A study of the leptonic backgrounds due to unidentified converted photon daughter tracks in semi-leptonic B decays has been conducted. The main tool in identifying converted photons at the BABAR experiment is a Photonic Conversion Finder (PCF) that has only been previously tested on Monte Carlo simulated data. The PCF is tested on a BABAR data sample containing Radiative Bhabha events. It was found that the PCF is able to properly identify two oppositely charged tracks as originating from a Photonic Conversion with a 70-80% isotropic efficiency above a converted photon energy of 0.5 GeV. This efficiency is slightly lower for converted photon energies below 0.5 GeV. The 70-80% efficiency plateau indicates that the PCF has an internal efficiency limit. The overall results of a comprehensive study on the lepton energy spectrum from tracks that were unidentified as originating from converted photons found that for every 2 tracks properly identified as originating from a Photonic Conversion, 2.4 tracks went unidentified. This result is due to both a low energy reconstruction inefficiency of the BABAR detector acting on highly asymmetric Photonic Conversions and to the internal efficiency limit of the PCF. In future studies at the BABAR experiment, users will be able to obtain the energy spectrum of leptons unidentified as originating from converted photons in their analysis by taking the energy spectrum of identified converted photons obtained in this thesis and scaling it to match their energy spectrum of identified converted photons.

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