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Track impact parameter resolution in the BaBar detector Asgeirsson, David J.

Abstract

This thesis contains a study of track impact parameter resolution in the BABAR detector using lepton pair events from e⁺e⁻ --> /⁺/⁻ (y) and from y*y* —> /⁺/⁻ where I is either e or μ,. The high number of these events in the data set and Monte Carlo simulations allows the tails of the resolution to be studied in detail. The Gaussian core of the resolution is consistent within 20% with the track-by-track errors returned by the track fitting software for both data and Monte-Carlo simulations. Beyond about three standard deviations (ϭ) the non-Gaussian tail approximately obeys power laws. A simple parametrization is presented which fits the data well to beyond 10 ϭ. The tail shape is consistent with that expected from a large-angle Coulomb scattering Toy Monte-Carlo. The GEANT4-based BABAR Monte Carlo software reproduces the core out to approximately 2a but the behaviour of the tails further out disagrees with the data and the predictions of Moliere theory.

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