This thesis presents the first observation of electroweak W+W- boson pair production in association with two jets in the fully leptonic final state. The analysis utilises data collected by the CMS detector from p-p collisions at a centre-of-mass energy of 13 TeV at the LHC between 2016 and 2018. Electroweak W+W- production belongs to the rare Vector Boson Scattering (VBS) processes, with cross sections in the fb range. The main background sources in this analysis come from top-antitop production, which can be reduced by vetoing jets containing b quarks. Additionally, there's the QCD-induced W+W- production, which can be minimised with strict kinematic cuts on jets. The Drell-Yan (DY) production contributes to background, particularly in the same flavor channels. The achievement of the final result is greatly attributed to the use of a deep neural network (DNN), which was trained to distinguish between the signal, and background from both top and QCD-induced W+W- production in the different flavor channel. The signal has been observed with a statistical significance of 5.6 standard deviations. Two distinct cross sections were measured in different fiducial phase spaces. These measurements represent the first determinations of the purely electroweak W+W- cross section and agree well with the SM predictions. VBS processes highlight the crucial role of the Higgs boson in maintaining unitarity in the SM. Any deviations from SM predictions could disrupt this balance, making the study of VBS cross-sections valuable for uncovering new physics phenomena. In cases where new physics might exist at energy scales beyond the LHC's reach, the adoption of an effective field theory (EFT) framework, such as the Standard Model Effective Field Theory (SMEFT), becomes a powerful tool for capturing potential effects. SMEFT extends the SM by introducing higher-dimensional operators based on SM fields and symmetries, making it suitable for accommodating extensions of the SM involving heavy particles. A second phase of this project aims to assess the expected sensitivities to 5 SMEFT operators in the W+W- VBS. We account for all background sources and uncertainties to replicate a realistic analysis. Our analysis relies on two 2D phase spaces, where the DNN output is plotted against two key observables: the invariant mass and transverse momentum of the dilepton system. The DNN output helps reduce the main backgrounds, and smultaneously, the two kinematic variables provide strong limits on the Wilson coefficients under study. The thesis additionally presents the research efforts directed towards enhancing the energy and timing reconstruction capabilities of the Electromagnetic Calorimeter (ECAL) for the high-luminosity phase of the LHC. When particles interact with crystals in the ECAL, a reconstruction algorithm is used to extract key information about the incident particles energy. The project was focused on the refinement and development of the Weights method, a reconstruction algorithm used for estimating signal amplitudes by calculating them through weighted combinations of time samples. Significantly, the modules developed for this project have been successfully integrated into the official CMS software.

Questa tesi presenta la prima osservazione della produzione elettrodebole di coppie di bosoni W+W- in associazione a due jet nello stato finale leptonico. L'analisi utilizza dati di LHC tra il 2016 e il 2018 raccolti dal rivelatore CMS da collisioni tra protoni a un'energia nel centro di massa di 13 TeV. La produzione elettodebole dei bosoni W+W- appartiene ai processi rari di scattering dei bosoni vettori (VBS), con sezioni d'urto nell'ordine dei femtobarn. Le principali fonti di background in questa analisi provengono dalla produzione di coppie top-antitop, che può essere ridotta applicando un veto ai jet contenenti quark b. Inoltre, c'è la produzione di W+W- indotta da processi QCD, che può essere ridotta mediante rigorosi tagli cinematici sui jet. La produzione di Drell-Yan (DY) contribuisce al background, in particolare nei canali con leptoni di stesso sapore. Il successo del risultato finale è in gran parte attribuito all'uso di una rete neurale (DNN), che è stata addestrata nello spazio fase con leptoni di sapore differente al fine di distinguere tra il segnale e il background derivante sia dalla produzione di top-antitop, sia da processi di produzione QCD di W+W-. Il segnale è stato osservato con una significatività statistica di 5.6 deviazioni standard. Sono state misurate due diverse sezioni d'urto in differenti spazi fase fiduciali. Queste misure rappresentano le prime determinazioni della sezione d'urto puramente elettrodebole di W+W- e concordano con le previsioni del Modello Standard (MS). I processi VBS evidenziano il ruolo cruciale del bosone di Higgs nel mantenere l'unitarietà nel MS. Qualsiasi deviazione dalle previsioni del MS potrebbe compromettere questo equilibrio, rendendo lo studio delle sezioni d'urto del VBS prezioso per scoprire nuovi fenomeni fisici. Nei casi in cui la nuova fisica potrebbe esistere a scale energetiche al di là della portata di LHC, l'adozione di un framework di Effective Field Theory (EFT), come la SMEFT, diventa uno strumento potente per catturare gli effetti potenziali. La SMEFT estende il MS introducendo operatori di dimensione superiore basati sui campi e le simmetrie del MS, rendendolo adatto ad accogliere estensioni del MS che coinvolgono particelle pesanti. Una seconda fase di questo progetto mira a valutare le sensibilità previste per 5 operatori SMEFT nel processo di W+W- VBS. Abbiamo considerato tutte le fonti di background e le incertezze per replicare un'analisi realistica. La nostra analisi si basa su due spazi fase bidimensionali, in cui l'output della DNN è rappresentato in funzione di due osservabili chiave: la massa invariante e il momento trasverso dei due leptoni carichi. L'output della DNN aiuta a ridurre i principali background, mentre le due variabili cinematiche forniscono limiti significativi sui coefficienti di Wilson. La tesi presenta inoltre gli sforzi di ricerca volti a migliorare le capacità di ricostruzione dell'energia e del timing del calorimetro elettromagnetico (ECAL) di CMS per la fase ad alta luminosità del LHC. Quando le particelle interagiscono con i cristalli in ECAL, un algoritmo di ricostruzione è utilizzato per estrarre informazioni sull'energia delle particelle incidenti. Questo progetto si è concentrato su perfezionamento e sviluppo del metodo dei pesi, un algoritmo di ricostruzione utilizzato per stimare le ampiezze del segnale, calcolandole attraverso combinazioni pesate dei campionamenti. I moduli sviluppati per questo progetto sono stati integrati con successo nel software ufficiale di CMS.

(2024). Observation of the electroweak production of W+W- bosons with two jets with the CMS detector at the LHC and searches for new physics with dimension-6 Effective Field Theory. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2024).

Observation of the electroweak production of W+W- bosons with two jets with the CMS detector at the LHC and searches for new physics with dimension-6 Effective Field Theory

PINOLINI, BIANCA SOFIA
2024

Abstract

This thesis presents the first observation of electroweak W+W- boson pair production in association with two jets in the fully leptonic final state. The analysis utilises data collected by the CMS detector from p-p collisions at a centre-of-mass energy of 13 TeV at the LHC between 2016 and 2018. Electroweak W+W- production belongs to the rare Vector Boson Scattering (VBS) processes, with cross sections in the fb range. The main background sources in this analysis come from top-antitop production, which can be reduced by vetoing jets containing b quarks. Additionally, there's the QCD-induced W+W- production, which can be minimised with strict kinematic cuts on jets. The Drell-Yan (DY) production contributes to background, particularly in the same flavor channels. The achievement of the final result is greatly attributed to the use of a deep neural network (DNN), which was trained to distinguish between the signal, and background from both top and QCD-induced W+W- production in the different flavor channel. The signal has been observed with a statistical significance of 5.6 standard deviations. Two distinct cross sections were measured in different fiducial phase spaces. These measurements represent the first determinations of the purely electroweak W+W- cross section and agree well with the SM predictions. VBS processes highlight the crucial role of the Higgs boson in maintaining unitarity in the SM. Any deviations from SM predictions could disrupt this balance, making the study of VBS cross-sections valuable for uncovering new physics phenomena. In cases where new physics might exist at energy scales beyond the LHC's reach, the adoption of an effective field theory (EFT) framework, such as the Standard Model Effective Field Theory (SMEFT), becomes a powerful tool for capturing potential effects. SMEFT extends the SM by introducing higher-dimensional operators based on SM fields and symmetries, making it suitable for accommodating extensions of the SM involving heavy particles. A second phase of this project aims to assess the expected sensitivities to 5 SMEFT operators in the W+W- VBS. We account for all background sources and uncertainties to replicate a realistic analysis. Our analysis relies on two 2D phase spaces, where the DNN output is plotted against two key observables: the invariant mass and transverse momentum of the dilepton system. The DNN output helps reduce the main backgrounds, and smultaneously, the two kinematic variables provide strong limits on the Wilson coefficients under study. The thesis additionally presents the research efforts directed towards enhancing the energy and timing reconstruction capabilities of the Electromagnetic Calorimeter (ECAL) for the high-luminosity phase of the LHC. When particles interact with crystals in the ECAL, a reconstruction algorithm is used to extract key information about the incident particles energy. The project was focused on the refinement and development of the Weights method, a reconstruction algorithm used for estimating signal amplitudes by calculating them through weighted combinations of time samples. Significantly, the modules developed for this project have been successfully integrated into the official CMS software.
PAGANONI, MARCO
GOVONI, PIETRO
LHC; CMS; VBS; EFT; ECAL
LHC; CMS; VBS; EFT; ECAL
FIS/04 - FISICA NUCLEARE E SUBNUCLEARE
English
22-gen-2024
36
2022/2023
open
(2024). Observation of the electroweak production of W+W- bosons with two jets with the CMS detector at the LHC and searches for new physics with dimension-6 Effective Field Theory. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2024).
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Descrizione: Observation of the electroweak production of W+W- bosons with two jets with the CMS detector at the LHC and searches for new physics with dimension-6 Effective Field Theory
Tipologia di allegato: Doctoral thesis
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/457519
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