The SLD vertex detector upgrade (VXD3) and a study of bbg events

Abstract

This thesis presents a variety of work concerning the design, construction and use of the SLD's vertex detector.

SLD's pioneering 120 Mpixel vertex detector, VXD2, was replaced by VXD3, a 307Mpixel CCD vertex detector in January 1996. The motivation for the up-grade detector and its subsquent construction and testing are described in some detail. This work represents the collaborative work of a large number of people. My work was mainly carried out at EEV on the testing of the CCDs and subsequent ladders. VXD3 was commissioned during the 1996 SLD run and performed very close to design specifications.

Monitoring the position of VXD3 is crucial for reconstructing the data in the detector for physics analysis. This was carried out using a capacitive wire position monitoring system. The system indicated that VXD3 was very stable during the whole of the 1996 run, except for known controlled movements. VXD3 was aligned globally for each period in-between these known movements using the tracks from e+e- → Z° → hadrons.

The structure of three-jet bbg events has been studied using hadronic Z° decays from the 1993-1995 SLD data. Three-jet final states were selected and the CCD-based vertex detector was used to identify two of the jets as a ь or ъ. The distributions of the gluon energy and polar angle with respect to the electron beam direction were examined and were compared with perturbative QCD predictions. If was found that the QCD Parton Shower prediction was needed to describe the data well. These distributions are potentially sensitive to an anomalous b chromomagnetic moment к. к was measured to be -0.031±0.038 0.039(Stat.)±0.003 0.004(Syst.), which is consistent with the Standard Model, with 95% confidence level limit, -0.106 < к < 0.044.