Search for third generation Leptoquarks in the CMS experiment at LHC
Description
Installed on the LHC (Large Hadron Collider) ring, the CMS experiment (Compact Muon Solenoid) recorded a great amount of proton-proton collisions data from 2009 to 2012 at center of mass energies of 7 TeV and 8 TeV. This experiment was designed for precise measurements of the Standard Model parameters, for Higgs boson studies and for testing theories beyond the standard model. Some of these theories foresee the existence of leptoquarks (LQ) which are new bosons with couplings to both leptons and quarks. The first part of this thesis is dedicated to a presentation of the Standard Model and to a leptoquarks theoretical introduction. The second one briefly explains how the LHC and the CMS experiment work. The third part details the work accomplished during the first year of my thesis in the CMS generator group. Finally, the last one deals with data analysis and the search of third generation leptoquarks pair production. Three LQ decay channels are investigated: to a top quark and a tau lepton, to a top quark and a neutrino and at last to a top quark and a muon. This study is based on the full integrated luminosity recorded during 2012, namely 19.7 fb. Various selections requiring at least one lepton and several jets are scrutinized in order to identify the regions with best signal efficiency regarding to Standard model backgrounds. Finally, a selection optimisation on discriminative variables is performed to extract the best limits at 95% confidence. No significant excess with respect to Standard Model expectations was found. Thus we were able to set limits on the leptoquarks pair production cross sections. Third generation leptoquarks with masses below 320 GeV, 240 GeV and 910 GeV are excluded for the top tau, top nu and top mu channels, respectively. (author)
Abstract (French)
L'experience CMS (Compact Muon Solenoid), construite sur l'anneau du LHC (Large Hadron Collider) a enregistre une quantite colossale de donnees provenant des collisions proton-proton de 2009 a 2012 a des energies dans le centre de masse de 7 TeVet 8 TeV. Cette experience est consacree aux mesures de precision des parametres du modele standard, a l'etude du boson de Higgs ainsi qu'a la mise a l'epreuve de theories au-dela du modele standard. Un certain nombre de ces theories prevoient l'existence de particules appelees leptoquarks, de nouveaux bosons se couplant a la fois aux leptons et au quarks. La premiere partie de cette these est consacree a la presentation du Modele Standard des particules et a une introduction theorique aux leptoquarks. La seconde presente brievement le fonctionnement du LHC et de l'experience CMS. La troisieme partie est dediee au travail effectue dans le groupe generateur de CMS au cours de la premiere annee de ma these. Cette mission consistait principalement a generer et a valider massivement des evenements Monte-Carlo avec le logiciel Madgraph pour l'ensemble de la collaboration CMS. Enfin, la derniere partie porte sur l'analyse de donnees et la recherche de paires de leptoquarks scalaires de troisieme generation. Trois canaux de desintegration des LQ sont envisages: en quark top et lepton tau, en quark top et neutrino et enfin en quark top et muon. Cette etude est basee sur l'ensemble des donnees enregistrees par l 'experience CMS au cours de l'annee 2012. Ce qui represente une luminosite integree totale de 19,7 fb. Differentes selections basees sur au moins un lepton et de nombreux jets sont examinees afin de definir les regions presentant les meilleures efficacites de signal par rapport au fond du Modele Standard. Enfin, une optimisation des coupures sur des variables tres discriminantes est realisee afin d'obtenir les meilleures limites a 95% de confiance sur les sections efficaces de production des leptoquarks. Aucun exces significatif par rapport aux previsions du modele standard n'a pu etre mis en evidence ce qui a permis de poser des limites sur les sections efficaces de production des leptoquarks. Les leptoquarks de troisieme generation sont exclus jusqu'a des masses de 320 GeV a 95 % de niveau de confiance pour le canal top tau, jusqu'a 240 GeV pour le canal top nu et jusqu'a 910 GeV pour le canal top mu. (auteur)
Files
Restricted
The record is publicly accessible, but files are restricted to users with access.
Additional details
Additional titles
- Original title (French)
- Recherche de leptoquarks de troisieme generation dans l'experience CMS au LHC
Publishing Information
- Imprint Pagination
- 162 p.
- Report number
- FRNC-TH--14360
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 54054455
- Subject category
- S72: PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; S43: PARTICLE ACCELERATORS;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- CERN LHC; CMS DETECTOR; COMPUTERIZED SIMULATION; DATA ANALYSIS; LEPTOQUARKS; M CODES; MASS; PARTICLE PRODUCTION; STANDARD MODEL; TEV RANGE 01-10
- Descriptors DEC
- ACCELERATORS; BOSONS; COMPUTER CODES; CYCLIC ACCELERATORS; DATA PROCESSING; ELEMENTARY PARTICLES; ENERGY RANGE; FIELD THEORIES; GRAND UNIFIED THEORY; MATHEMATICAL MODELS; MEASURING INSTRUMENTS; PARTICLE MODELS; POSTULATED PARTICLES; PROCESSING; QUANTUM FIELD THEORY; RADIATION DETECTORS; SIMULATION; STORAGE RINGS; SYNCHROTRONS; TEV RANGE; UNIFIED GAUGE MODELS
Optional Information
- Notes
- 106 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses