Zofia Czyczula

Title: Search for New Physics in Tau-pair Events in ATLAS at the LHC

A thesis submitted for the degree of Doctor of Philosophy on June 2009 - defended August 27, 2009.

Supervisor:
Mogens Dam

Abstract

Search for New Physics in Tau-pair Events in ATLAS at the LHC

With the start-up of the Large Hadron Collider (LHC), a new world-largest particle accelerator, an exciting period in particle physics research will begin. ATLAS, one of the two general purpose detectors constructed at the LHC, is intended to search for new phenomena which involve highly massive particles whose detection was beyond the reach of past, lower-energy experiments.

In this thesis, the potential of ATLAS to discover a new heavy particle in the two tau lepton final state is discussed based on fully simulated data samples. The tau-pair signature is important as it is sensitive to particles which couple preferentially to the third generation fermions as well as it offers potential for measuring polarisation asymmetry. It is shown that such particle could be discovered in this channel already at early stage of ATLAS operation. After collecting more data, measurement of tau polarisation would then provide an interesting constraint on the nature of the resonance.

Searches for new physics in channels involving taus require excellent understanding of tau leptons' signatures in the ATLAS detector. Development of an algorithm for efficient and robust identification of hadronically decaying taus is a team work of many people in ATLAS. Improvements to the algorithm are also discussed in the thesis.