Search for stable and long-lived heavy charged particles in electron-positron collisions at center of mass energies from 130 to 209 GeV with the OPAL detector at LEP.

摘要

A search for stable and long-lived massive particles of electric charge |Q/e| = 1 or fractional charges of 2/3, 4/3 and 5/3, produced in electron-positron collisions is reported in this thesis. The search is performed on data collected at center of mass energies from 130 to 209 GeV, by the OPAL detector at LEP. The existence of such particles is predicted by several supersymmetric theoretical scenarios beyond the Standard Model of particle physics. Because of their charge and high mass, such particles would yield an anomalous ionization, dE/dx. The data analysis presented is a topological search based on the very accurate dE/dx measurement of the OPAL detector. These massive charged particles are assumed to be pair-produced in electron-positron collisions and not to interact strongly. No evidence of the production of these particles is observed. Therefore model-independent upper limits on the production cross-section are derived. The results are also interpreted within the framework of the Constrained Minimal Supersymmetric Model (C-MSSM), obtaining mass lower limits for scalar muons and scalar taus. All mass and cross-section limits are derived at 95% confidence level and are valid for particles with lifetimes longer than 10−6 s.