Dissertations / Theses on the topic 'Lepton number'

In this work we add a Dirac right-handed neutrino superfield to the Minimal Supersymmetric Standard Model (MSSM). We discuss the interactions of the right- handed (RH) sneutrino and its mixing with its left-handed counterpart. We study the possibility of this RH sneutrino to be the lightest supersymmetrie particle (LSP). We obtain that this dark matter candidate is a non-thermal relic, and generally has a small relic density. This we argue makes it an interesting candidate for addressing the Ω(_DM)/ Ω(_b) problem. We then discuss a lepton-number conserving leptogenesis scenario, in which an Affleck-Dine inspired mechanism generates a left-right asymmetry in the sneutrino sector. The left-handed part of this asymmetry eventually genesis mechanism, as the right-handed part of the left-right asymmetry becomes the observed dark matter density.

The Standard Model does not describe several phenomena, such as gravity and dark matter, and therefore is an incomplete description of nature. This demands the existence of new physics beyond the Standard Model. Two searches for new physics are presented in this thesis, along with a sensitivity study for a third analysis sensitive to new physics. The vMSM model motivates a search for lepton number violation using B+ -> h- μ+ μ+ decays, where h = (pi, K). No B+ → h- μ+ μ+ candidates are seen in ~ 36 pb -1 of LHCb data and limits are set of BR (B+ → K- μ+ μ+) < 4.1 x 10 -8 and BR (B+ → pi- μ+ μ+) < 4.4 x 10 -8 at 90\% C.L. These improve the previous best limits by a factor 40 and 30, respectively. Using ~ 1fb -1 of LHCb data, the B+ → pi+ μ+ μ- decay is observed for the first time with 5.2 sigma significance. This is the first b → dμ+μ- transition to be observed. The B+→ pi+ μ+ μ- branching fraction is measured to be (2.3 ± 0.6 (stat) ± 0.1 (syst)) x 10 -8. The ratio of branching fractions between B+ → pi+ μ+ μ- and B+ → K- μ+ μ- is measured to be 0.053 ± 0.014 (stat) ± 0.001 (syst), and this is used to determine a value of the ratio of quark mixing matrix elements Vtd| /Vtd| = 0.266 ± 0.035 (stat) ± 0.003 (syst). All of these results are compatible with the Standard Model expectations. Previous measurements of the ratio of B → D(*)τ+v and B → D(*)μ+v branching fractions exceed the Standard Model expectations by more than 3 sigma, combining D and D*. These decays are challenging to measure at a hadron collider, due to the presence of neutrinos in the final state. A sensitivity study is presented for a measurement of the ratio of B0 → D*τ+v and B0 → D*-μ+v branching fractions at LHCb. This study includes a novel fit method, and two new algorithms which enable the backgrounds to be controlled, and control samples to be isolated. The estimated uncertainty on Rd*, including the largest systematic uncertainties, is ~ 8\%, competitive with the 9\% uncertainty on the present best measurement of Rd*.

The GERmanium Detector Array (GERDA) experiment, located underground at the INFN Laboratori Nazionali del Gran Sasso (LNGS) in Italy, uses high-purity germanium detectors to search for neutrinoless double beta decay (0νββ) of Ge-76. The first phase of the experiment lasted from November 2011 to May 2013 and collected data with a total exposure of 21.6 kg · yr. In this thesis, a thorough analysis of these data was performed. A background model was developed to decompose the observed energy spectrum in its individual contributions. The region around the Q-value of 0νββ, Qββ , at 2039 keV was studied in great detail. As main contributions to the background in this region, alpha and beta decays of the U-238 chain, beta decays of the Th-232 chain, and beta decays of K-42 were identified. It was shown that the background around Qββ can be approximated with a flat distribution. Neutrino accompanied double beta decay (2νββ) is a lepton number conserving process allowed by the Standard Model. Due to the low background in the experiment, in the region dominated by 2νββ a signal-to-background ratio of 3 : 1 could be reached. This allowed to measure the half-life of the decay with a precision unprecedented by previous experiments, T1/2^2ν = (1.96 ± 0.13) · 10^21 yr. Several beyond-Standard Model theories predict neutrinoless double beta decay with majoron emission (0νββχ(χ)). Depending on the theory, this process can be lepton number violating or lepton number conserving. A search in the GERDA Phase I data gave no indication of contributions to the observed energy spectra for any of the majoron models. The lower limit on the half-life for the ordinary majoron model (spectral index n = 1) was determined to be T1/2^0νχ > 4.15 · 10^23 yr (90 % quantile). This limit and the limits derived for the other majoron modes constitute the most stringent limits on 0νββχ(χ) of Ge-76 measured to date. The primary scope of the GERDA experiment was the search for 0νββ of Ge-76. This lepton number violating decay is expected by extensions of the Standard Model. The observation of 0νββ would be the proof that the neutrino has a non-vanishing Majorona mass component. The analysis of the GERDA Phase I data did not reveal any hint for the presence of a signal from 0νββ. A lower limit on the half-life was derived, T1/2^0ν > 1.83 · 10^25 yr (90 % quantile).
L’esperimento GERmanium Detector Array (GERDA), situato nei Laboratori Nazionali del Gran Sasso (LNGS) dell’INFN, utilizza rivelatori al germanio ultra-puro per la ricerca del doppio decadimento beta senza neutrini (0νββ). Tali rivelatori sono arricchiti nell’isotopo Ge-76. La prima fase dell’esperimento è durata da novembre 2011 a maggio 2013 ed ha raccolto dati con un’esposizione totale di 21.6 kg · yr. In questa tesi è stato sviluppato dapprima un modello dei fondi per scomporre lo spettro energetico osservato nei suoi singoli componenti. La regione intorno al Q-valore della reazione 0νββ, Qββ , a 2039 keV è stata studiata in modo dettagliato. I contributi principali al fondo in questa regione sono: i decadimenti alfa e beta della catena del U-238, i decadimenti beta della catena del Th-232 ed i decadimenti beta del K-42. È stato dimostrato inoltre che il fondo intorno a Qββ può essere descritto con una costante. Il doppio decadimento beta con emissione di due neutrini (2νββ) è un processo che conserva il numero leptonico ed è previsto dal Modello Standard. Nella regione dominata dagli eventi 2νββ è stato raggiunto un rapporto fra segnale e fondo di 3 : 1. Questo risultato ha permesso di misurare il tempo di dimezzamento del decadimento con una precisione ineguagliata dagli esperimenti precedenti, T1/2^2ν = (1.96 ± 0.13) · 10^21 yr. Alcuni modelli di fisica oltre il Modello Standard prevedono il doppio decadimento beta senza neutrini con emissione di uno o due majoroni (0νββχ(χ)). In base alla teoria, questo processo può violare o conservare il numero leptonico. Un’analisi dei dati della prima fase di GERDA non ha fornito alcun riscontro di contributi di uno di questi modelli agli spettri energetici osservati. Il limite inferiore sul tempo di dimezzamento per il modello ordinario del majorone (indice spettrale n = 1) è stato stimato pari a T1/2^0νχ > 4.15 · 10^23 yr (quantile del 90 %). Questo valore e quelli ricavati per altri modelli del majorone costituiscono i limiti più stringenti su 0νββχ(χ) nel Ge-76 misurati fino ad ora. Lo scopo primario dell’esperimento GERDA è la ricerca del 0νββ nel Ge-76. Questo processo, che viola il numero leptonico, è previsto dalle estensioni del Modello Standard e la sua osservazione dimostrerebbe che la massa del neutrino ha una componente di tipo Majorana. L’analisi dei dati della prima fase di GERDA non ha rivelato nessun cenno della presenza di un segnale di 0νββ. È stato così determinato un limite inferiore sul tempo di dimezzamento, T1/2^0ν > 1.83 · 10^25 yr (quantile del 90 %).

A search for the Lepton Number Violating decay \(K\)\(^±\) → \(π\)\(^∓\)\(μ\)\(^±\)\(μ\)\(^±\) has been performed using the data collected by the NA48/2 experiment in 2003 and 2004. The signal event selection, the background rejection, the evaluation of the muon identification efficiency and the statistical methods used for the data interpretation are presented. Based on 1.8 x 10\(^1\)\(^1\) kaon decays in the fiducial volume and using several models for the signal, upper limits for the branching ratio \(B\)(\(K\)\(^±\) → \(π\)\(^∓\)\(μ\)\(^±\)\(μ\)\(^±\)) of the order of 10\(^-\)\(^1\)\(^0\) have been obtained for 90%, 95% and 99% confidence levels, improving the previous best limit of one order of magnitude. The Cherenkov differential counter used for kaon identification in the NA62 experiment, equipped with approximately 30% of the photo-detectors, was installed and tested during a Technical Run in 2012. The counter's ability of distinguishing between kaons and pions has been validated via pressure scan procedure. The data collected have been used for evaluating the kaon efficiency and time resolution. The extrapolation to the full-sized detector has been also estimated.

SNO+ is a liquid scintillator experiment whose physics goals include measurements of solar neutrinos, reactor anti-neutrinos, geo neutrinos and double beta decay. During an initial water phase, it will also search for invisible modes of nucleon decay. This thesis investigates methods of improving the detector's sensitivity to the baryon and lepton violating processes of neutrinoless double beta decay and invisible nucleon decay. It does this through an improved scintillator model, allowing the sensitivity of the detector with different loading techniques to be evaluated, through a new background rejection technique, capable of increasing the active volume of the detector, and with the development of improved position fitters, achieving resolutions of approximately 10 cm in scintillator and 25 cm in water. The sensitivity of SNO+ to invisible modes of nucleon decay is explored, predicting, after one month of data, a limit of t > 1.38 x 10³⁰ years on the decay of neutrons and of t > 1.57 x 10³⁰ years on the decay of protons.

This thesis presents work carried out using data from the LHCb experiment during the first three years of data taking, 2010 - 2012. A study of the effects of radiation damage on the silicon sensors of the LHCb Vertex Locator is performed, with an emphasis on the implications for the long term performance of the detector. Following three years of operation the sensors have received a maximum delivered neutron equivalent fluence of approximately 1.6E12 per square centimeter, leading to a number of radiation induced effects. In particular the change in charge collection efficiency and signal/noise with fluence is compared to theoretical expectations, and the current trends are extrapolated to the fluences expected at the end of the LHCb detector lifetime. The development of an unexpected effect due to the structure of the routing lines in the sensors is described in detail. Searches for lepton flavour and baryon number violating decays of the tau lepton using the 2011 LHCb dataset are described. Observation of any lepton flavour or baryon number violation would be an unambiguous sign of new physics, whilst setting improved limits helps to constrain a number of Beyond the Standard Model theories. First LHCb limits are set on the branching fractions of the decays tau- to mu- mu+ mu-, tau- to anti-proton mu+ mu- and tau- to proton mu- mu-, with these results also representing the first limits on lepton flavour violating tau decays at a hadron collider. The limit on tau- to mu- mu+ mu- is expected to approach the world's best result from Belle in the coming years whilst the tau- to anti-proton mu+ mu- and tau- to proton mu- mu- results constitute the first limits on the branching fractions of these decays. The future prospects for these measurements with further data are briefly described.

The search for the neutrinoless double beta (0nbb) decay is one of the most active fields in modern particle physics. This process is not allowed within the Standard Model and its observation would imply lepton number violation and would lead to the Majorana nature of neutrinos. The experimentally observed quantity is the half-life of the decay, which can be connected to the effective Majorana neutrino mass via nuclear matrix elements. The latter can only be determined theoretically and are currently affected by large uncertainties. To reduce these uncertainties one can investigate the well established two-neutrino double beta (2nbb) decay into the ground and excited states of the daughter isotope. These similar processes are allowed within the Standard Model. In this dissertation, the search for 2nbb decays into excited states is performed in Pd-110, Pd-102 and Ge-76. Three gamma spectroscopy setups at the Felsenkeller (Germany), HADES (Belgium) and LNGS (Italy) underground laboratories are used to search for the transitions in Pd-110 and Pd-102. No signal is observed leading to lower half-live bounds (90% C.I.) of 2.9e20 yr, 3.9e20 yr and 2.9e20 yr for the 0/2nbb 2p1, 0p1 and 2p2 transitions in Pd-110 and 7.9e18 yr, 9.2e18 yr and 1.5e19 yr for the 0/2nbb 2p1, 0p1 and 2p2 transitions in Pd-102, respectively. This is a factor of 1.3 to 3 improvement compared to previous limits. The data of Phase I (Nov 2011 - May 2013) of the 0nbb decay experiment GERDA at LNGS is used to search for excited state transitions in Ge-76. The analysis is based on coincidences between two detectors and finds no signal. Lower half-life limits (90 % C.L.) of 1.6e23 yr, 3.7e23 yr and 2.3e23 yr are obtained for the 2nbb 2p1, 0p1 and 2p2 transitions, respectively. These limits are more than two orders of magnitude larger than previous ones and could exclude many old matrix element calculations. In addition to the excited state searches, important measurements and improvements for GERDA Phase II upgrades are performed within this dissertation. 30 new BEGe detectors are characterized for their surface and active volume properties which is an essential ingredient for all future physics analyses in GERDA. These precision measurements reduce the systematic uncertainty of the active volume to a subdominant level. In extension to this, a new model for simulating pulse shapes of n+ electrode surface events is developed. With this model it is demonstrated that the dominant background of K-42 on the detector surfaces can be suppressed by a factor of 145 with an A/E pulse shape cut in Phase II. A further suppression of background is obtained by a liquid argon scintillation light veto. With newly developed Monte Carlo simulations, including the optical scintillation photons, it is demonstrated that Tl-208 in the detectors holders can be suppressed by a factor of 134. K-42 homogeneously distributed in the LAr can be suppressed with this veto in combination with pulse shape cuts by a factor of 170 for BEGe detectors. The characterization measurements and the developed simulation tools presented within this dissertation will help to enhance the sensitivity for all 0/2nbb decay modes and will allow to construct an improved background model in GERDA Phase II
Die Suche nach dem neutrinolosen Doppelbetazerfall (0nbb) ist eines der aktivsten Felder der modernen Teilchenphysik. Der Zerfall setzt die Verletzung der Leptonenzahl voraus und hätte die Majorananatur des Neutrinos zur Folge. Die durch eine Beobachtung bestimmbare Halbwertszeit des Zerfalls ermöglicht, über ein nukleares Matrixelement, Zugang zur effektiven Majorananeutrinomasse. Die größten Unsicherheiten gehen dabei auf das Matrixelement zurück, welches nur durch verschiedene, teilweise stark voneinander abweichende theoretische Modelle zugänglich ist. Eine Möglichkeit diese Unsicherheiten zu reduzieren bieten genaue Studien des im Standardmodel erlaubten neutrinobegleiteten Doppelbetazerfalls (2nbb) in angeregte Zustände des Tochterkerns. In dieser Dissertation wird der 2nbb-Zerfall der Nuklide Pd-110, Pd-102 und Ge-76 in angeregte Zustände untersucht. Die Untersuchungen von Pd-110 und Pd-102 wurden in drei umfangreichen Gammaspektroskopie-Experimenten in den Untergrundlaboren Felsenkeller (Deutschland), HADES (Belgien) und LNGS (Italien) durchgefürt. Es wurde kein Signal beobachtet und damit die weltweit besten unteren Grenzen für die Halbwertszeit dieser Zerfälle festgesetzt: 2,9e20 yr, 3,9e20 yr und 2,9e20 yr für die 0/2nbb 2p1, 0p1 und 2p2 Übergänge in Pd-110 and 7,9e18 yr, 9,2e18 yr und 1,5e19 yr für die 0/2nbb 2p1, 0p1 und 2p2 Übergänge in Pd-102 (90% C.I.). Dies ist eine 1,3 bis 3-fache Verbesserung gegenüber den vorher bekannten Grenzen. Die Untersuchung des 2nbb-Zerfalls in Ge-76 basiert auf Daten aus Phase I (Nov. 2011 - Mai 2013) des 0nbb-Zerfall Experiments GERDA. Mit der auf koinzidenten Ereignissen basierten Analyse konnte kein Signal beobachtet werden und folgende untere Grenzen für die Halbwertszeit der 2nbb 2p1, 0p1 und 2p2 Übergänge wurden festgelegt: 1,6e23 yr, 3,7e23 yr und 2,3e23 (90% C.L.). Diese 100-fache Verbesserung gegenüber den bisher bekannten Grenzen widerlegt eine Vielzahl älterer, zur Verfügung stehender Matrixelemente. Zusätzlich wurden im Rahmen dieser Dissertation für die Erweiterungen des GERDA Experiments zur Phase II wichtige Messungen durchgeführt und Verbesserungen entwickelt. 30 neu produzierte BEGe Detektoren wurden hinsichtlich ihrer Oberflächeneigenschaften sowie ihrer aktiven Volumina charakterisiert. Diese Präzisisionsmessungen sind für alle zukünftigen Analysen in GERDA notwendig und erlauben die entsprechenden systematischen Unsicherheiten auf ein subdominantes Niveau zu reduzieren. Erweiternd wurde ein neues Model zur Beschreibung der n+ Elektrode entwickelt, welches erstmals erlaubt die Pulsform von Oberflächeninteraktionen zu simulieren. Mithilfe dieses Models konnte demonstriert werden, dass der in Oberflächeninteraktionen begründete und in GERDA dominante Messuntergrund von K-42 auf der Detektoroberfläche durch Pulsformanalyse um das 145-fache unterdrückt werden kann. Eine weitere Untergrundreduzierung wird durch ein Flüssigargon Szintillationsveto erreicht. Im Rahmen dieser Arbeit wurden vorhandene Monte Carlo Simulationen um den Transport von optischen Photonen erweitert und die 134-fache Unterdrückung des Tl-208 Untergrundes demonstriert. Die Ergebnisse dieser Arbeit helfen eine deutliche Sensitivitätsverbesserung für die zuküntige Suche nach dem 0/2nbb-Zerfall zu erzielen und erlauben die Erstellung eines präziseren Untergrundmodels in GERDA Phase II

The search for the neutrinoless double beta (0nbb) decay is one of the most active fields in modern particle physics. This process is not allowed within the Standard Model and its observation would imply lepton number violation and would lead to the Majorana nature of neutrinos. The experimentally observed quantity is the half-life of the decay, which can be connected to the effective Majorana neutrino mass via nuclear matrix elements. The latter can only be determined theoretically and are currently affected by large uncertainties. To reduce these uncertainties one can investigate the well established two-neutrino double beta (2nbb) decay into the ground and excited states of the daughter isotope. These similar processes are allowed within the Standard Model. In this dissertation, the search for 2nbb decays into excited states is performed in Pd-110, Pd-102 and Ge-76. Three gamma spectroscopy setups at the Felsenkeller (Germany), HADES (Belgium) and LNGS (Italy) underground laboratories are used to search for the transitions in Pd-110 and Pd-102. No signal is observed leading to lower half-live bounds (90% C.I.) of 2.9e20 yr, 3.9e20 yr and 2.9e20 yr for the 0/2nbb 2p1, 0p1 and 2p2 transitions in Pd-110 and 7.9e18 yr, 9.2e18 yr and 1.5e19 yr for the 0/2nbb 2p1, 0p1 and 2p2 transitions in Pd-102, respectively. This is a factor of 1.3 to 3 improvement compared to previous limits. The data of Phase I (Nov 2011 - May 2013) of the 0nbb decay experiment GERDA at LNGS is used to search for excited state transitions in Ge-76. The analysis is based on coincidences between two detectors and finds no signal. Lower half-life limits (90 % C.L.) of 1.6e23 yr, 3.7e23 yr and 2.3e23 yr are obtained for the 2nbb 2p1, 0p1 and 2p2 transitions, respectively. These limits are more than two orders of magnitude larger than previous ones and could exclude many old matrix element calculations. In addition to the excited state searches, important measurements and improvements for GERDA Phase II upgrades are performed within this dissertation. 30 new BEGe detectors are characterized for their surface and active volume properties which is an essential ingredient for all future physics analyses in GERDA. These precision measurements reduce the systematic uncertainty of the active volume to a subdominant level. In extension to this, a new model for simulating pulse shapes of n+ electrode surface events is developed. With this model it is demonstrated that the dominant background of K-42 on the detector surfaces can be suppressed by a factor of 145 with an A/E pulse shape cut in Phase II. A further suppression of background is obtained by a liquid argon scintillation light veto. With newly developed Monte Carlo simulations, including the optical scintillation photons, it is demonstrated that Tl-208 in the detectors holders can be suppressed by a factor of 134. K-42 homogeneously distributed in the LAr can be suppressed with this veto in combination with pulse shape cuts by a factor of 170 for BEGe detectors. The characterization measurements and the developed simulation tools presented within this dissertation will help to enhance the sensitivity for all 0/2nbb decay modes and will allow to construct an improved background model in GERDA Phase II.
Die Suche nach dem neutrinolosen Doppelbetazerfall (0nbb) ist eines der aktivsten Felder der modernen Teilchenphysik. Der Zerfall setzt die Verletzung der Leptonenzahl voraus und hätte die Majorananatur des Neutrinos zur Folge. Die durch eine Beobachtung bestimmbare Halbwertszeit des Zerfalls ermöglicht, über ein nukleares Matrixelement, Zugang zur effektiven Majorananeutrinomasse. Die größten Unsicherheiten gehen dabei auf das Matrixelement zurück, welches nur durch verschiedene, teilweise stark voneinander abweichende theoretische Modelle zugänglich ist. Eine Möglichkeit diese Unsicherheiten zu reduzieren bieten genaue Studien des im Standardmodel erlaubten neutrinobegleiteten Doppelbetazerfalls (2nbb) in angeregte Zustände des Tochterkerns. In dieser Dissertation wird der 2nbb-Zerfall der Nuklide Pd-110, Pd-102 und Ge-76 in angeregte Zustände untersucht. Die Untersuchungen von Pd-110 und Pd-102 wurden in drei umfangreichen Gammaspektroskopie-Experimenten in den Untergrundlaboren Felsenkeller (Deutschland), HADES (Belgien) und LNGS (Italien) durchgefürt. Es wurde kein Signal beobachtet und damit die weltweit besten unteren Grenzen für die Halbwertszeit dieser Zerfälle festgesetzt: 2,9e20 yr, 3,9e20 yr und 2,9e20 yr für die 0/2nbb 2p1, 0p1 und 2p2 Übergänge in Pd-110 and 7,9e18 yr, 9,2e18 yr und 1,5e19 yr für die 0/2nbb 2p1, 0p1 und 2p2 Übergänge in Pd-102 (90% C.I.). Dies ist eine 1,3 bis 3-fache Verbesserung gegenüber den vorher bekannten Grenzen. Die Untersuchung des 2nbb-Zerfalls in Ge-76 basiert auf Daten aus Phase I (Nov. 2011 - Mai 2013) des 0nbb-Zerfall Experiments GERDA. Mit der auf koinzidenten Ereignissen basierten Analyse konnte kein Signal beobachtet werden und folgende untere Grenzen für die Halbwertszeit der 2nbb 2p1, 0p1 und 2p2 Übergänge wurden festgelegt: 1,6e23 yr, 3,7e23 yr und 2,3e23 (90% C.L.). Diese 100-fache Verbesserung gegenüber den bisher bekannten Grenzen widerlegt eine Vielzahl älterer, zur Verfügung stehender Matrixelemente. Zusätzlich wurden im Rahmen dieser Dissertation für die Erweiterungen des GERDA Experiments zur Phase II wichtige Messungen durchgeführt und Verbesserungen entwickelt. 30 neu produzierte BEGe Detektoren wurden hinsichtlich ihrer Oberflächeneigenschaften sowie ihrer aktiven Volumina charakterisiert. Diese Präzisisionsmessungen sind für alle zukünftigen Analysen in GERDA notwendig und erlauben die entsprechenden systematischen Unsicherheiten auf ein subdominantes Niveau zu reduzieren. Erweiternd wurde ein neues Model zur Beschreibung der n+ Elektrode entwickelt, welches erstmals erlaubt die Pulsform von Oberflächeninteraktionen zu simulieren. Mithilfe dieses Models konnte demonstriert werden, dass der in Oberflächeninteraktionen begründete und in GERDA dominante Messuntergrund von K-42 auf der Detektoroberfläche durch Pulsformanalyse um das 145-fache unterdrückt werden kann. Eine weitere Untergrundreduzierung wird durch ein Flüssigargon Szintillationsveto erreicht. Im Rahmen dieser Arbeit wurden vorhandene Monte Carlo Simulationen um den Transport von optischen Photonen erweitert und die 134-fache Unterdrückung des Tl-208 Untergrundes demonstriert. Die Ergebnisse dieser Arbeit helfen eine deutliche Sensitivitätsverbesserung für die zuküntige Suche nach dem 0/2nbb-Zerfall zu erzielen und erlauben die Erstellung eines präziseren Untergrundmodels in GERDA Phase II.

The neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We show the viability of the sterile neutrino hypothesis as dark matter component, together with the characteristic features of this scenario in the minimal Inverse Seesaw mechanism. The possibility of successfully accounting for the baryon asymmetry in a testable realisation of the leptogenesis mechanism is also addressed. On the other hand it is important to look for manifestations of sterile fermions in laboratory experiments. We address this point by making predictions for the expected rates of rare lepton number violating decays of vector bosons, that can be mediated by sterile fermions, as well as by studying the impact of sterile fermions on global fit of electroweak precision data.

Made available in DSpace on 2015-05-14T12:14:18Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 939261 bytes, checksum: f8a1456cf29d5789dabc615e68c9a352 (MD5) Previous issue date: 2009-08-28
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The standard model does not predict mass for the neutrinos, and any evidence that neutrinos are massive particles is a signal of new physics. Recent experimental data on neutrino oscillations provide a convincing evidence that neutrinos are massive and very light particles, with mass in the scale of eVs. Thus, we must extend the standard model in order to incorporate mass terms for the neutrinos, and find a mechanism to explain the value of observed masses. It is almost a consensus that the See-Saw mechanism provides the most elegant explanation for the observed value of the masses of neutrinos. In this work we implement the See-Saw mechanism in the 3-3-1 model with right handed neutrinos. The implementation is made with the introduction of a scalar sextet and the spontaneous breaking of the lepton number. We identi fied the Majoron as a singlet by the group SU(2)LNU(1)y, which makes it safe under the current limits of the eletroweak data. The main result of this work is that the See-Saw mechanism works at the TeV scale, and as a result the mass of right handed neutrinos lies in the electroweak scale, providing a great opportunity to test their existence in the current detectors. Finally we present one of the most interesting properties of the model, the Flavour Changing Neutral Current (FCNC). We show the explicit form of this lagrangian and motivate the study of this phenomenon through Hadronic and leptonic interactions that enable their testability in the next generation of accelerators.
O modelo padrão não prediz massa para os neutrinos, e qualquer evidência que os neutrinos sejam partículas massivas é um sinal de nova física. Dados experimentais recentes sobre oscilações de neutrinos fornecem uma evidência convincente de que os neutrinos são partículas massivas e muito leves, com massa na escala dos eVs. Assim, devemos estender o modelo padrão de forma tal que sejam incorporados termos de massa para os neutrinos, e encontrar um mecanismo que explique o valor das massas observadas. É quase um consenso que o mecanismo See-Saw proporciona a mais elegante explicação para o valor observado das massas dos neutrinos. Neste trabalho implementamos o mecanismo See-Saw no modelo 3-3-1 com neutrinos de mão direita, 3 - 3 - 1RHV. A implementação é feita com a introdução de um sexteto escalar e a quebra espontânea do número leptônico. Identificamos o Majoron como um singleto pelo grupo SU(2)LNU(1)y, o que o torna seguro sob os atuais limites dos dados eletrofracos. O principal resultado deste trabalho é que o mecanismo See-Saw funciona na escala dos TeVs, e como resultado a massa dos neutrinos de m~ao direita encontra-se na escala eletrofraca, fornecendo uma grande oportunidade de testar a sua existência nos atuais detectores. Finalmente, apresentamos uma das propriedades mas interessantes do modelo, a troca de sabor na corrente neutra (FCNC). Mostramos a forma explícita desta lagrangiana e motivamos o estudo deste fenômeno por meio de interações hadrônicas e leptônicas que possibilitam sua testabilidade na próxima geração de aceleradores.

Cette thèse présente la première mesure de la section efficace exclusive photon-photon-> di-leptons en collisions proton-proton à une énergie dans le centre de masse de 7 TeV dans l'expérience ATLAS au LHC. La mesure est réalisée avec toutes les données accumulées en 2011, pour une luminosité intégrée de 4.6/fb. La première partie de la thèse est dédiée à la description théorique de ce type d'interaction. Le calcul de l'amplitude de la réaction photon-photon-> di-leptons est bien connu dans le cadre du modèle standard de la physique des particules. Cependant, une complication apparaît au LHC avec la prise en compte des effets de taille finie du proton. Le calcul de cet effet est l'une de mes contributions personnelles. Il a donné lieu à une publication. La section efficace nominale est réduite d'environ 20% du fait de cet effet, ce qui n'est pas négligeable. La seconde partie de la thèse concerne la description des détecteurs de l'expérience ATLAS. J'y décris en particulier le travail que j'ai réalisé sur la simulation de certains de ces détecteurs, en particulier les détecteurs situés dans la ligne de vol des protons, qui permettent la mesure de la trajectoire de ces derniers. Enfin, la dernière partie de la thèse concerne la mesure expérimentale de la section efficace de la réaction photon-photon-> di-leptons en collisions proton-proton, comme mentionnée plus haut. Lorsque la paire de leptons est une paire de muons, on trouve que la section efficace exclusive est égale à 0.628 ± 0.032(stat) ± 0.021(syst) pb, pour le domaine cinématique suivant M(di-muons)>20 GeV, pT(muons)>10 GeV et |muons)<2.4. Lorsque la paire de leptons est une paire électron-positrons, nous avons obtenu une section efficace exclusive égale à 0.428 ± 0.035(stat) ± 0.018(syst) pb, pour M(ee)>24 GeV, pT(e)>12 GeV et |muons (e)|<2.4. De plus, ces mesures confirment que le facteur de réduction par rapport à la prédiction théorique nominale (sans prendre en compte les effets de taille finie du proton) est bien de 20% dans le domaine d'énergie de la mesure. Cette analyse a été publiée par la collaboration ATLAS. Une perspective pour cette mesure est de la réaliser à plus haute énergie avec les nouvelles données accumulées par l'expérience ATLAS à partir de 2015. De plus, une mesure directe de la trajectoire des protons pourrait aider à la sélection exclusive
This thesis presents a first measurement of the exclusive cross section for the reaction photon-photon-> di-leptons in proton-proton collisions at center of mass energy of 7 TeV in the ATLAS experiment at the LHC. The measurement is realized with all data accumulated during the year 2011 with an integrated luminosity of 4.6/fb. The first part of the thesis is dedicated to the theoretical description of this kind of interactions. The calculus of the amplitude for the reaction photon-photon-> di-leptons is well known in the context of the standard model of particle physics. However, the situation at the LHC is more complex. It requires taking into account the finite size effects of the protons. The understanding of this effect and its evaluation is one of my personal contributions, which has been published. The nominal cross section is then reduced by about 20% following this effect, which is non negligible. The second part of the thesis concerns the description of the detectors of the ATLAS experiment. In particular, I describe the work I have realized on the simulation of some of these devices, mainly the detectors located in the direction of flight of the protons that allows a measurement of the trajectory of the scattered (intact) protons. Finally, the last part of the thesis is devoted to the experimental measurement of the cross section of the reaction photon-photon-> di-leptons in proton-proton collisions, as mentioned above. When the lepton pair is a pair of muons, we find an exclusive cross section of 0.628 ± 0.032(stat) ± 0.021(syst) pb, for the kinematical domain M(di-muons)>20 GeV, pT(muons)>10 GeV and |muons|<2.4. When the lepton pair is a pair of electrons (positrons), we have obtained an exclusive cross section of 0.428 ± 0.035(stat) ± 0.018(syst) pb, for M(ee)>24 GeV, pT(e)>12 GeV et |muons(e)|<2.4. Moreover, these measurements confirm that the reduction (suppression) factor with respect to the nominal theory prediction (without taking into account the finite size effect of the protons) is of the order of 20% in the energy domain of the measurement. A perspective for this work is to make the measurement at larger energy with the new data recorded by the ATLAS experiment since 2015. Moreover, a direct measurement of the trajectory of protons could help for the exclusive selection

Experiments E799 Phase-II (E799II) and E832 of the Kaons at the TeVatron (KTeV) project at the Fermi National Accelerator Laboratory (Fermilab), are in the process of studying rare and CP-violating kaon decays. The experiment ran during 1996 and 1997, and the resulting data are being analyzed. This study focuses on the E7991I search for the decay mode KL→p0m+/- e∓ , and its accompanying background decays, in approximately 60% of the 1996--7 KTeV data.

Experiments E799 Phase-II (E79911) and E832 of the Kaons at the TeVatron (KTeV) project at the Fermi National Accelerator Laboratory (Fermilab) were designed to study rare and CP-violating kaon decays. The experiments ran first during 1996 and 1997, and then again during 1999. This study focused on the E799II search for the lepton-flavor-violating decay mode KL → pi 0mu+/-e∓, and on its accompanying background decays, in the full set of 1996--7 and 1999 KTeV data. For the combined data sets, we calculated a new 90% confidence level branching ratio limit BR(KL → pi 0mu+/-e∓) < 3.37 x 10-10.

The discovery of the Higgs boson by the LHC provided the last piece of the puzzle neces- sary for the Standard Model (SM) to be a successful theory of electroweak scale physics. However there exist various phenomenological reasons which serve as pointer towards the existence of physics beyond the Standard Model. For example the explanation for the smallness of the neutrino mass, baryon asymmetry of the universe, the presence of dark matter and dark energy etc. are not within purview of the Standard Model. Con- ceptual issues like the gauge hierarchy problem, weakness of gravity provide some of the theoretical motivation to pursue theories beyond the SM. We consider scenarios with warped extra-dimensions (Randall-Sundrum (RS) Model ) as our preferred candidate to answer some of the questions raised above. RS model gives an elegant geometric solution to address the hierarchy between the two fundamental scales of nature i.e. Planck scale and electroweak scale. In addition to this, the geometry of RS serves as a useful setup wherein the fermion mass hierarchy problem can also be solved. The goal of this thesis is to investigate whether RS model can be an acceptable theory of avour while at the same time serving as a solution to the hierarchy problem. In Chapter[1] we begin with a brief introduction of the SM, highlighting issues which pro- vides the necessary motivation for constructing new physics models. Various candidates of Beyond Standard Model (BSM) physics are introduced and a few preliminaries es- sential to understand frameworks with additional spatial-dimensions ( at and warped) is provided. In Chapter[2] we specialize to the case of warped extra-dimensions and motivate the need to have the SM elds in the bulk. Mathematical details related to the analysis of various spin elds (0; 12; 1 and 2) in a warped background necessary to understand relevant phenomenology is provided. The lack of knowledge of Dirac or Majorana nature of the neutrino leads to a wide variety of possibilities as far as neutrino mass generation is concerned. In Chapter[3] we focus on the leptonic sector where three cases of neutrino mass generation are consid- ered: a)Planck Scale lepton number violation (LLHH case) b) Dirac neutrinos c) Bulk Majorana mass terms. We then study the implications of each case on the charged lepton mass tting. The case with Planck scale lepton number violation in normal RS scenario requires large and negative values for the bulk mass parameters for the charged singlets cE. Dirac neutrinos and the case with Bulk Majorana mass terms give good t to data. For completeness, the ts for the hadronic sector is provided in the appendix. In Chapter[4] avour violation for each of three cases introduced in Chapter[3] is studied. For the case with Planck scale lepton number violation, the non-perturbative Yukawa coupling between the SM singlets and the KK states render the higher order diagrams incalculable. Lepton avour violation (LFV) is particularly large for the Dirac case and the bulk Majorana case for low Kaluza-Klein(KK) mass scales. We then invoke the ansatz of Minimal Flavour violation to suppress LFV with low lying KK scales and examples of avour group is provided for both cases. In Chapter[5] we present an example with a type II two Higgs doublet model applied to the LLHH case. The setup o ers a solution where LLHH scenario can be consistently realized in RS model, where the masses and mixing angles in the leptonic sector can bet with O(1) choice of bulk parameters. Assumption of global lepton number conservation (like in Dirac neutrinos) could lead to problems in theories of quantum gravity where it does not hold. This leads us to the question whether Dirac neutrinos can be naturally realized in nature. In Chapter[6] we consider the special case of bulk Majorana mass encountered in Chapter[3] where the bulk Dirac mass terms for the right handed neutrino is set to zero. We nd that this leads to a case where the e ective zero mode neutrino mass is of Dirac type with negligible e ects from the tower of Majorana states. In Chapter[7] we consider RS at the GUT scale which no longer serves as a solution to the hierarchy problem. SUSY is introduced in the bulk and the low energy SUSY serves as a solution to the hierarchy problem. Such models serve as a useful alternative to SUSY models with family symmetries (e.g. Froggatt-Nielsen Model). However the solutions to the Yukawa hierarchy problem are constrained due to anomaly cancellation conditions. In Chapter[8] supersymmetry breaking due to radion mediation in addition to brane localized sources is considered and detailed analysis of the running of soft masses and the low energy avour observables is considered for both cases separately. In Chapter[9] we conclude and present future directions.

The works presented in this thesis explore a variety of extensions of the standard model of particle physics which are motivated by baryon number (B) and lepton number (L), or some combination thereof. In the standard model, both baryon number and lepton number are accidental global symmetries violated only by non-perturbative weak effects, though the combination B-L is exactly conserved. Although there is currently no evidence for considering these symmetries as fundamental, there are strong phenomenological bounds restricting the existence of new physics violating B or L. In particular, there are strict limits on the lifetime of the proton whose decay would violate baryon number by one unit and lepton number by an odd number of units.

The first paper included in this thesis explores some of the simplest possible extensions of the standard model in which baryon number is violated, but the proton does not decay as a result. The second paper extends this analysis to explore models in which baryon number is conserved, but lepton flavor violation is present. Special attention is given to the processes of μ to e conversion and μ → eγ which are bound by existing experimental limits and relevant to future experiments.

The final two papers explore extensions of the minimal supersymmetric standard model (MSSM) in which both baryon number and lepton number, or the combination B-L, are elevated to the status of being spontaneously broken local symmetries. These models have a rich phenomenology including new collider signatures, stable dark matter candidates, and alternatives to the discrete R-parity symmetry usually built into the MSSM in order to protect against baryon and lepton number violating processes.

The three-dimensional (3D) baroclinic response of Cayuga Lake to surface wind forcing was investigated using the fully nonhydrostatic MITgcm. The model was validated against observed temperature data using a hydrostatic 450 m (horizontal) grid and both qualitative and quantitative methods. The model correctly reproduces the basin-scale dynamics (e.g., seiche with horizontal mode-one period T1 = 80 h) with a basin-wide root-mean-square error of 1.9 C. Nonlinear internal surges were visualized to evolve due to (i) a wind-induced locally downwelled thermocline (wind duration Twind < T1/4), (ii) a basin-scale wind-induced upwelled thermocline (Twind > T1/4), (iii) internal hydraulic jumps (IHJs). Results from a 113 m grid and field observations were used to characterize the basin-scale internal wave field according to composite Froude number (G2), Wedderburn number (WN), and Lake number (LN). The typical Cayuga Lake response is a surge when ~ 1 < WN (LN) < ~ 2-12 and a surge with emergent nonlinear internal waves (NLIWs) when WN or LN < ~ 2, in agreement with published laboratory studies. An observed shock front was simulated to be an IHJ, occurring at mid-basin during strong winds when WN < 0.8. This is the first simulation of a mid-basin seiche-induced IHJ due to super critical conditions (G2 > 1) in a lake. The topographic-induced IHJs were also shown to form when the surges interact with a sill-contraction topographic feature. Both high-resolution hydrostatic and nonhydrostatic models were used to investigate the evolution, propagation and shoaling of NLIWs at medium lake-scale. A nonhydrostatic 22 m grid with lepticity λ ~ 1 ensures minimal numerical relative to physical dispersion, qualitatively reproducing observed dispersive NLIWs using ~ 2.3E+8 grid cells. Solitary waves evolve with almost unchanged wavelengths upon grid refinement from 40 m (λ ~ 2) to 22 m; suggesting model convergence to the correct solution. Corresponding hydrostatic grids were shown to produce a packet of narrower spurious solitary-like motions with different wavelengths, representing a balance between nonlinear steepening and numerical dispersion. Local gyre-like patterns and secondary transverse NLIW packets were visualized to result from wave-topography interaction, suggesting that NLIW propagation in long narrow lakes, where the bottom topography has irregularities is fundamentally 3D.
Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-12-14 12:45:21.727