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Search for the Standard Model Higgs boson in the four leptons decay channel with multivariate analysis at the ATLAS experiment

The purpose of this thesis is the search for the Higgs boson in the four leptons decay channel. The traditional analysis based on some selection cuts has been integrated with a multivariate one in order to increase the power of discrimination between signal and background processes.

Mostra/Nascondi contenuto.
Chapter1 The Standard Model and The Higgs Boson The Standard Model (SM) is a successful theory incorporating the present understanding of fundamental particles and their interactions. The SM is per- turbativeatsucientlyhighenergiesandrenormalizableduetoitsgaugeinvari- ant formulation. It is able to accommodate basically all the known experimen- tal facts and precise measurements performed in high energy particles colliders over the last decades. However it remains \incomplete": the existence of dark matter and the gravitational interaction are not described; the mechanism for electroweak symmetry breaking that gives masses to the particles is not iden- tied, and the associated particle, the Higgs boson, has not been observed yet. ThereforeitiscrucialtoprovetheHiggsexistenceandthevalidityofthetheory or completely exclude it over the entire allowed mass range. This chapter briey describes the Standard Model and its key ingredients with some attention to the mechanism which predicts the existence of the Higgs par- ticle and describes the origin of the masses of the fundamental particles. Then it will discuss the Higgs boson production, decay modes and the limits on its mass. 1.1 The Standard Model (SM) 1.1.1 Particles and Interactions In our current understanding, the physical world is composed by a few fun- damental building blocks, which are collectively called matter, and is shaped by their interactions, which are collectively called forces. In the Standard Model particles can be divided in two categories: fermions and bosons [1]. 6

Tesi di Laurea Magistrale

Facoltà: Scienze Matematiche, Fisiche e Naturali

Autore: Cristina Papaleo Contatta »

Composta da 183 pagine.


Questa tesi ha raggiunto 14 click dal 15/05/2012.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.