ISBN 91-628-2804-5
LUNFD6/(NFFL-7150) 1997

The search for a standard model Higgs at the LHC and electron identification using transition radiation in the ATLAS tracker

By due permission of the faculty of mathematics and natural sciences at Lund University, to be publicly discussed at the lecture hall B of the Department of Physics, January 16th 1998 at 2.15pm for the degree of Doctor of Philosophy

by


Ulrik Egede

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Elementary Particle Physics,
Lund University,
Box 118,
SE-221 00 Lund,
Sweden.

An automatic translation of this thesis from LaTeX to html was performed. In some places text or figures are slightly modified because of limitations and bugs in the translation programme. In case of doubt the PostScript version should always be consulted. In special should be noted that many equation numbers are incorrect; the references with hyperlinks to them are, however, always correct.

Abstract:

The Large Hadron Collider (LHC) will be ready for proton-proton collisions in the year 2005 and the ATLAS detector will be one of the two experiments at the LHC which will explore a new and higher energy range for particle physics. In this thesis, an analysis of the power of the ATLAS detector to detect a Standard Model Higgs boson has been performed. It is shown that it will be possible to discover a Higgs particle across the complete mass range from the lower limit defined by the reach of the LEP2 collider experiments to the upper theoretical limit around 1 TeV. The role of the inner tracking detector of ATLAS for the detection of conversions and the identification of the primary vertex in the detection of a Higgs particle in the H $\rightarrow$ $\gamma$$\gamma$ decay channel is demonstrated with a detailed detector simulation. The identification of a 1 TeV Higgs particle requires a good understanding of both the signal and the backgrounds. The related uncertainties are covered in detail and it is shown that the Higgs can be identified in the H $\rightarrow$ W ⁺W ^- $\rightarrow$ l$\nu$jj , H $\rightarrow$ ZZ $\rightarrow$ l ⁺l ^-$\nu$$\bar{\nu}$ and H $\rightarrow$ ZZ $\rightarrow$ l ⁺l ^-jj decay channels. The Transition Radiation Tracker (TRT) is a combined tracking an electron identification device which will be a part of the inner tracking detector of ATLAS. For a prototype of the TRT the electron identification performance is analysed and it is shown that the full scale TRT together with the calorimeters will provide the electron identification power required for a clean electron and photon signal at the LHC. For the prototype a rejection factor of 100 against pions was achieved with an electron efficiency of 90%. The importance of the TRT for a clear detection of a Higgs particle is demonstrated.