b-Tagging and the Search for Neutral Supersymmetric Higgs Bosons at DØ

A search for neutral supersymmetric Higgs bosons and work relating to the improvement of the b-tagging and trigger capabilities at the DØ detector during Run II of the Fermilab Tevatron collider is presented. The search for evidence of the Higgs sector in the Standard Model (SM) and supersymmetric extensions of the SM are a high priority for the DØ collaboration, and b-tagging and good triggers are a vital component of these searches. The development and commissioning of the first triggers at DØ which use btagging is outlined, along with the development of a new secondary vertex b-tagging tool for use in the Level 3 trigger. Upgrades to the Level 3 trigger hit finding code, which have led to significant improvements in the quality and efficiency of the tracking code, and by extension the b-tagging tools, are also presented. An offline Neural Network (NN) b-tagging tool was developed, trained on Monte Carlo and extensively tested and measured on data. The new b-tagging tool significantly improves the b-tagging performance at DØ, for a fixed fake rate relative improvements in signal efficiency range from ∼ 40% to ∼ 15%. Fake rates, for a fixed signal efficiency, are typically reduced to between a quarter and a third of their value. Finally, three versions of the search for neutral supersymmetric Higgs bosons are presented. The latest version of the analysis makes use of almost 1 fb−1 of data, the new NN b-tagger and the new b-tagging triggers, and has set one of the world’s best limits on the supersymmetric parameter tanβ in the mass range 90 to 150 GeV.