Development of an object oriented C++ algorithm for b-quark identification (Development of methods of b-quark identification in high energy $e^+e^-$ and pp collisions)

In the past thirty years particle physics has developed rapidly resulting in the formulation of the Standard Model, which seems to provide, at least in principle, a microscopic description for all known physical phenomena except gravity. The Standard Model is not complete, e.g. it lacks any explanation for the pattern of particle masses. The Higgs mechanism provides a solution to the problem of how particles acquire their masses. It implies the existence of at least one new particle, the Higgs boson H0 , which has not yet been observed. The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) will be switched on in winter 2007. If the Higgs boson exists, the LHC will be able to detect it. Depending on the mass of the Higgs boson, physicists have a clear idea regarding its experi- mental signature. For quite low masses (50 < mH0 < 130[ GeV]) )1 the Higgs will predominantly decay into two b-quarks. The present study describes the investigation of the identification ca- pability of b-quark signatures in the CMS experiment at the LHC. In order to test the b-quark identification methods developed, the data of the ALEPH experiment recorded at the LEP e+ e− storage ring from 1992 till 1995 are used. Chapter 1 is divided in three parts. The first part describes basic concepts of the Standard Model and the properties of b-quark decays, which can be utilized to identify (tag) them. The second part describes the foundations of the measurement of Rb at the Z0 resonance with the ALEPH experiment. The measurement of Rb , which is the partial decay width of the Z0 boson ̄ into bb-quark pairs2 , is used as a benchmark to tune the b-quark identification strategies. The current status of the Higgs boson search and the discovery potential of the CMS experiment for a light Higgs boson decaying into two b-quarks is summarized in the third part of chapter 1. The measurement of Rb at the Z0 resonance employing the developed b-tag strategy is de- scribed in chapter 2. About 3.8 million events collected by the ALEPH experiment from 1992 to 1995 together with the corresponding simulated data are utilized. Chapter 3 describes the discovery potential of the CMS experiment for the Higgs produced in association with a W± boson. The study is based on simulated data obtained from the full detector simulation. The analysis investigates the features and the expected performance of the b-tag developed above.