Dissertations / Theses on the topic 'CP Higgs'

An alternative approach to the problem of CP-violation is presented. It is based on the possibility of spontaneous CP-breakdown in models with two Higgs doublets. General features of the phenomenon such as stability of the vacuum and the existence of a light axion are discussed. We investigate the feasibility of spontaneously broken CP in the minimal supersymmetric models - the MSSM and NMSSM. The latter is shown to be experimentally viable. The phenomenological implications of the model such as CP-violating effects in the kaon systems and a nonzero neutron electric dipole moment are studied.
Ph. D.

Orientador: Ricardo D'Elia Matheus
Banca: Oscar José Pinto Eboli
Banca: Rogério Rosenfeld
Resumo: Consideramos o decaimento do Higgs violando sabor leptônico h→ 'tau' 'mü' no contexto de teorias efetivas. O CMS divulgou recentemente um excesso de eventos de 2,5 'sigma' neste canal. O operador responsável por este processo, no entanto, está em muitos casos correlacionado com operadores de dipolo, que já têm fortes restrições experimentais. Exploramos então em que casos é possível de se obter um operador de violação de sabor grande o suficiente para ser visto em decaimentos do Higgs no LHC, porém ainda respeitando os limites encontrados em decaimentos radiativos de léptons. Apresentamos também dois modelos, um do tipo Higgs Composto e outro do tipo Higgs Portal, mostrando como o processo h→ 'tau' 'mü' surge em cada um deles. Caso o sinal do CMS seja confirmado, o segundo modelo será favorecido, enquanto é improvável que o primeiro consiga o explicar
Abstract: We consider the Higgs Lepton Flavor Violating decay h→ 'tau' 'mü' in the framework of effective theories, on which CMS reported a 2.5 σ excess of events. The operator that is responsible for this process, however, is in many models correlated to dipole operators that are already under stringent experimental constraints. We then explore in which cases it is possible to obtain a flavor violating operator that is big enough to be seen in Higgs decays at the LHC, while still respecting the leptonic radiative decay bounds. We also present two models, a simplified Composite Higgs model and a Higgs Portal model, showing how the process h→ 'tau' 'mü' is generated in each of them. We find that if the CMS signal is confirmed, the second model is favored, while it is unlikely that the first model will be able to explain it
Mestre

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Consideramos o decaimento do Higgs violando sabor leptônico h→ 'tau' 'mü' no contexto de teorias efetivas. O CMS divulgou recentemente um excesso de eventos de 2,5 'sigma' neste canal. O operador responsável por este processo, no entanto, está em muitos casos correlacionado com operadores de dipolo, que já têm fortes restrições experimentais. Exploramos então em que casos é possível de se obter um operador de violação de sabor grande o suficiente para ser visto em decaimentos do Higgs no LHC, porém ainda respeitando os limites encontrados em decaimentos radiativos de léptons. Apresentamos também dois modelos, um do tipo Higgs Composto e outro do tipo Higgs Portal, mostrando como o processo h→ 'tau' 'mü' surge em cada um deles. Caso o sinal do CMS seja confirmado, o segundo modelo será favorecido, enquanto é improvável que o primeiro consiga o explicar
We consider the Higgs Lepton Flavor Violating decay h→ 'tau' 'mü' in the framework of effective theories, on which CMS reported a 2.5 σ excess of events. The operator that is responsible for this process, however, is in many models correlated to dipole operators that are already under stringent experimental constraints. We then explore in which cases it is possible to obtain a flavor violating operator that is big enough to be seen in Higgs decays at the LHC, while still respecting the leptonic radiative decay bounds. We also present two models, a simplified Composite Higgs model and a Higgs Portal model, showing how the process h→ 'tau' 'mü' is generated in each of them. We find that if the CMS signal is confirmed, the second model is favored, while it is unlikely that the first model will be able to explain it

Complete one-loop results are presented for neutralino and Higgs decay processes of the form chi^0_i->chi^0_j h_a and h_a->chi^0_i chi^0_j in the MSSM with CP-violating parameters. An on-shell renormalisation scheme is developed for the chargino–neutralino sector that consistently takes into account imaginary parts arising from complex parameters and absorptive parts of loop integrals. The genuine vertex contributions are combined with two-loop Higgs propagator-type corrections to obtain the most precise prediction currently available for this class of processes. In the CP-violating CPX benchmark scenario, the corrections to the neutralino decay width are found to be particularly large – of order 45% for a Higgs mass of 40GeV. We find that in this unexcluded parameter region, which will be difficult to cover by standard Higgs search channels at the LHC, the branching ratio for the decay chi^0_2->chi^0_1 h_1 is large. This may offer good prospects of detecting such a light Higgs boson in cascade decays of supersymmetric particles. We also study the full Higgs production and decay processes in scenarios where the intermediate Higgs bosons are nearly mass degenerate and interference effects can have a significant impact. We find that an on-shell approximation gives results in good numerical agreement with the full momentum-dependent Higgs propagator matrix calculation and we develop a generalised narrow width approximation to be used in such a situation. We use these methods to study the asymmetry between the production of left-handed and right-handed neutralinos in Higgs decays at the LHC in the presence of CP-violating phases. Large asymmetries are found to be possible for large M_H^± > 500GeV and tan beta < 10, where the decay into neutralinos may be the only possibility to detect the heavy Higgs bosons.

In this work, the B->
X_dell ell decays are examined in the context of a CP softly broken two Higgs doublet model. The differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries of the final lepton in this decay are studied. The dependencies of these physical parameters on the model parameters are analyzed by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP violating effects. It has been found that NHB effects are quite significant for the tau mode and the above-mentioned observables seems to be promising as a testing ground for new physics beyond the SM, especially for the existence of the CP-violating phase in the theory.

The last few years witnessed some major breakthroughs in the field of fundamental particle physics, which had a big impact in our understanding of Nature at a microscopic level. On March 30th, 2010, the first proton-proton collisions took place at the Large Hadron Collider (LHC), marking the beginning of a new era in particle physics. The excellent performance of the machine and the detectors, due to the fantastic work of all the researchers involved in the experiments, lead, in only two years, to the announcement of the discovery of the Higgs boson on July 4th, 2012. This event could be considered as the peak of success for the Standard Model (SM) of elementary particles, which predicted the existence of this particle – as well as all its properties – since more than forty years before. In the following two years the ATLAS and CMS experiments at the LHC measured the properties of the Higgs particle with a good accuracy, showing no significant deviation from the SM. In the meanwhile, also the numerous direct searches for other new particles turned out to give only negative results, against all expectations from the theory community, pushing the scale of new physics to higher and higher values. Also, while the cosmological evidence for Dark Matter (DM) is now stronger than ever, so far all direct and indirect searches provided negative results (albeit with some isolated exceptions which, however, are still much debated in the literature and seem to be incompatible with other negative results) and the bounds on weakly interacting massive particle DM are extremely strong. In neutrino physics an important event took place in June 2011, when the Tokay-to-Kamioka (T2K) collaboration reported an evidence for a non-zero, and sizable, value of the reactor neutrino mixing angle, θ13. This was confirmed in March 2012 by the Daya Bay collaboration, which measured this mixing angle with a very high precision, confirming that its value lies on the high-end of previous upper bounds. Since many popular and well motivated models of neutrino mixing predicted a zero, or very small, value of the reactor angle, this result was very important and offered a new insight in the quest for understanding the origin of flavor in the lepton sector. Also, since CP violation in the lepton sector effects vanish in the θ13 → 0 limit, the fact that this angle is sizable opens up many interesting possibilities for measuring CP violation in the neutrino sector. The work presented in this thesis was largely stimulated by these two major breakthroughs in particle physics. On the one hand the Higgs discovery and the measurement of its properties, in particular its mass, lead us to study the consequences of these measurements for a specific class of models beyond the SM: composite Higgs models (and also in supersymmetric versions of these models). In particular, we found that a very definite (and testable) prediction for the spectrum of new physics can be obtained: fermionic top partners are expected to be near the ∼1TeV scale. Also, the measurements of the Higgs couplings and the fact that the bounds for the new physics scale are often much higher than the electroweak scale, open up the possibility of studying possible deformations from the SM in an effective field theory framework. In this context we studied the possibility of linking the properties of the Higgs with other electroweak observables, very well constrained by LEP, via renormalization group effects, finding that they already allow to derive constraining, and independent, bounds on some Higgs properties. In the future, when some deviation from the SM will be – hopefully – observed, these effects could provide a new window on the new physics sector. On the other hand, we studied how the measured value of θ13 can be accommodated in some motivated models of neutrino mixing by exploiting corrections due to the mixing among the charged leptons. Such corrections are expected, for example, in Grand Unified Theories, which allow to link the charged lepton sector with the quark sector, and therefore the neutrino mixing matrix with the quark mixing one. This analysis allowed us to obtain a precise prediction for the value of the Dirac CP violating phase in neutrino mixing, testable by future neutrino experiments.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this thesis we study the phenomenological consequences of several CP-violating structures that could arise in the Standard Model effective field theory framework. Focusing on operators involving electroweak gauge and/or Higgs bosons, we derive constraints originating from Run I LHC data. We then study the capabilities of the present and future LHC runs at higher energies to further probe associated CP-violating phenomena and we demonstrate how differential information can play a key role. We consider both traditional four-lepton probes of CP-violating in the Higgs sector and novel new physics handles based on varied angular and non-angular observables.
Nesta tese é estudado as consequências fenomenológicas de diversas estruturas que violam a simetria CP, surgidas no contexto do modelo padrão efetivo. Focando nos operadores que envolvem os bósons de calibre e o Higgs, estabelecemos vínculos provenientes dos dados do RUN I do LHC. Em seguida, é estudada a capacidade do RUN I e de futuros RUNs do LHC em sondar os fenômenos associados à violação de CP e é demonstrado como as informações provenientes das distribuições diferencias podem desempenhar um papel chave para determinação destes vínculos. Para sondar efeitos físicos de violação de CP, consideramos tanto as sondagens tradicionais utilizando o canal de decaimento do Higgs em 4 léptons assim como novos observáveis angulares e cinemáticos empregados em diferentes canais de produção e decaimento do Higgs.

It is widely believed that the Standard Model (SM) can not be a fundamental theory of the basic interactions. Originated from this fact, many new physics models have been proposed. Among them, the two Higgs doublet model (2HDM), the SM enlarged by adding one extra scalar doublet, is considered as the simplest extension of the SM. In this work, within the framework of the model III version of the 2HDM, the exclusive decay the branching ratio is calculated and discussed in various physical regions determined by model parameters. It is observed that it is possible to reach present experimental upper limits in model Finally, the avor changing top quark decay,

This thesis presents two measurements performed in the $Htautau$ channel and based on the proton-proton collisions data collected by the ATLAS experiment during 2015 and 2016 and corresponding to an integrated luminosity of 36.1~fb$^{-1}$. The $Htautau$ is a considerably important decay channel because it allows to directly measure the Higgs Yukawa coupling and to probe the Higgs boson properties. Measurements of the Higgs production cross section in the $Htautau$ decay channel are presented. The observed (expected) significance of the $H ightarrow au au$ signal excess over the expected background amounts to 4.4 (4.1) standard deviations. This result, combined with the data taken at $sqrt{s}=7$ and 8 TeV, leads to an observed (expected) significance of 6.4 (5.4) and constitutes the first ATLAS observation of $H ightarrow au au$. The measured total cross section of $H ightarrow au au$, using the data collected at $sqrt{s}=13$~TeV, is $3.77^{+0.60}_{-0.59}~( ext{stat.})~^{+0.87}_{-0.74}~( ext{syst.})$~pb which is consistent with the Standard Model expectation. In addition, total cross sections for the vector boson fusion and gluon-gluon fusion processes have been measured separately and similar results are reported based on the simplified template cross section framework. All of these measurements are in agreement with the Standard Model predictions. The second measurement presented in this manuscript concerns a CP violation study in the same decay channel. The coupling structure of the vertex where the Higgs couples to two electroweak gauge bosons in its vector boson fusion production is investigated. The Optimal Observable method is used to directly test CP invariance in this vertex. No sign of CP violation is observed and constraints on the $ ilde{d}$ parameter, which governs the strength of CP violation, have been set. A 68% CL interval is observed for $ ilde{d}$ of [-0.090, 0.035], compared to an expected interval of $ ilde{d} in [-0.035, 0.033]$. No constraints can be set at 95% CL despite an expected interval $ ilde{d} in [-0.21, 0.15]$ at 95% CL was determined.

Après la découverte du boson de Higgs en 2012 au LHC, l'intérêt s'est porté sur l'étude de ses propriétés pour vérifier le Modèle Standard et pour sonder la nouvelle physique. L'une de ses propriétés fondamentales est sa spin-parité (CP), dont le Modèle Standard prédit la valeur 0+. Les analyses menées sur les données récoltées au Run 1 du LHC ont rejeté toutes les hypothèses d'état pur de spin-parité autre que cette valeur. Cependant des états mixtes de CP sont toujours possibles, ce qui indiquerait une violation de symmétrie CP dans le secteur du Higgs.La première partie de cette thèse se concentre sur la calibration du calorimètre électromagnétique d'ATLAS permettant d'atteindre une résolution de l'ordre du pour mille sur l'énergie des électrons et photons, primordiaux dans les analyses du boson de Higgs. Une des étapes est l'inter-calibration des couches du calorimètre électromagnétique, corrigeant des effets résiduels de calibration électronique et de diaphonie (cross-talk). La méthode établie au Run 1 a montré ses limites devant les niveaux d'empilement mesurés au Run 2, et une nouvelle analyse a été alors dévéloppée, assurant le contrôle précis des incertitudes systématiques.La deuxième partie de cette thèse porte sur la mesure des couplages CP-impairs du boson de Higgs aux boson vecteurs, étudié dans le canal de désintégration du boson de Higgs en quatre leptons. Malgré une faible statistique, ce canal offre une signature propre et un rapport signal sur bruit de plus de deux, permettant l'analyse précise des propriétés du boson de Higgs. Le mode de production par fusion de bosons vecteurs offre la meilleure sensibilité aux effets de CP grâce à la présence de deux jets dans l'état final. La pollution venant du mode de production par fusion de gluon avec des jets additionels est réduite grâce à l'utilisation de réseaux neuronaux. Pour distinguer de manière univoque les effets CP-impair d'éventuels effets CP-pair encore inconnus, une nouvelle variable est construite dont l'asymétrie de forme dépend uniquement d'effets CP-impairs. Composée d'éléments de matrice, cette variable utilise les informations cinématiques du boson de Higgs et des jets de manière maximale. Les résultats sont interprétés en termes de théorie effective, et la sensibilité statistique à 68% de confiance sur le coefficient de Wilson tCzz est estimée à [-0.80, 0.80]
After the Higgs boson discovery at the LHC in 2012, interest turned to Higgs boson property measurements to refine the tests of the Standard Model and probe for new physics. One of its key properties is its spin-parity (CP), predicted to be 0+ in the Standard Model. Analyses of data collected during the Run 1 of the LHC rejected all pure spin-parity (CP) state other than 0+. However mixed CP states are still possible, and would indicate CP violation in the Higgs sector.The first part of this thesis focuses on the ATLAS electromagnetic calorimeter calibration, needed to reach a permil level on electron and photon energy resolution which are of prime importance for Higgs boson studies. One step of the calibration sequence consists of the layer intercalibration of the electromagnetic calorimeter, needed to correct residual electronics miscalibration and cross-talk effects. The Run 1 method has proven to be unreliable for the pileup levels in Run 2 and a new method was developed, ensuring a precise control on the systematic uncertainties.The second part of this thesis puts emphasis on the Higgs boson to vector boson CP-odd couplings, with the Higgs boson decaying to four leptons. This channel, despite low statistics, provides a clean signature and a signal-to-noise ratio over two, allowing for a precise determination of the Higgs boson properties. The vector boson fusion production channel offers the best sensitivity to CP effects thanks to its two characteristic tagging jets in the final state. The contamination from the gluon fusion production mode with additional jets is reduced using neural networks. To unambiguously distinguish yet unknown CP-even from possible CP-odd effects, a variable whose shape asymmetry only depends on CP-odd effects is built. This observable is based on the matrix element computation, maximally using the kinematic information available from Higgs boson and associated jets. Results are interpreted in a context of effective field theory, and the statistical precision on the tCzz Wilson coefficient is estimated to [-0.80, 0.80] at the 68% confidence level

A test of CP invariance in Higgs boson production via Vector Boson Fusion using the optimal observable method is presented. The analysis exploits the decay mode of the Higgs boson into a pair of tau leptons in the decay channels H → TlTl and H → TlT_had and is based on 20.3 fb⁻¹ of proton-proton collision data at √s = 8 Tev collected by the ATLAS experiment at the LHC. CP-violating interactions between the Higgs boson and electroweak gauge bosons are described in an effective field theory framework, where the strength of CP violation is governed by a single parameter d̃. The mean values and distributions of CP-odd observables agree with the expectation in the Standard Model and show no sign of CP violation. The CP-mixing parameter d̃ is constrained to the interval [-0.11, 0.05] at the 68% confidence level, consistent with the Standard Model expectation of d̃ = 0.

la physique des particules s'appuie sur une théorie dont les prédictions sont mesurables dans les grands collisionneurs. Les résultats obtenus confortent cette theorie electrofaible de basse énergie mais aucune déviation aujourd'hui n'annonce de la nouvelle physique. Ce qui devient étonnant, c'est qu'aucun des résultats ne confortent les observations venant de l'Univers. Que ce soit pour expliquer la baryogénèse primordiale ou la matière et l'énergie noire, responsable de l'acceleration de l'expansion de l'Univers. Dans cette habilitation, j'ai retracé quelques résultats électrofaibles du LEP (Higgs et boson W) ainsi que des mesures de violation CP. Je les compare aux attentes cosmologiques en terme de baryogénése primordiale et de quantité d'énergie noire et je montre que le modèle Standard actuel ne peut repondre a ces questions. Je finis par une analyse des approches théoriques et expérimentales pour répondre à ce grand problème actuel.

A Monte Carlo simulation is performed of Higgs decays in the H → ZZ → 4l channel at ATLAS. Decay parameters are varied in order to model Higgs decays of differing CP states. A full analysis is performed, including trigger and background studies. Using various angular distributions as observables it is found that ATLAS should be able to exclude an anomalous CP odd coupling at 50 fb−1 and an anomalous CP even coupling at 100 fb−1. The CP violating case studied could not be excluded.
Graduate

Model Standardowy (The Standard Model (SM)) opisuje z powodzeniem oddziaływa- nia cząstek elementarnych, jednak pozostawia bez odpowiedzi wiele podstawowych pytań. Przedstawiana rozprawa doktorska dotyczy niektórych z otwartych zagadnień. Głównym celem rozprawy jest zbadanie i zrozumienia pochodzenia występującej we Wszechświecie asymetrii między materią a antymaterią oraz natury ciemnej materii (Dark Matter (DM)). Bariogeneza, czyli kreacja asymetrii barionowej (BAU) jest od dawna otwartym problemem kosmologii. Sakharov sformułował warunki aby taki proces kreacji wystąpił- niezachowa- nie liczby barionowej B, łamanie symetrii ładunkowej C i symetrii kombinowanej CP oraz odstępstwo od równowagi termicznej. Wśród wielu scenariuszy proponowanych w ostatnich dekadach – bariogeneza elektrosłaba (Electroweak EW) jest jednym z bardziej interesujących podejść. Jak się okazuje, oddziaływania elektrosłabe tak jak je ujmuje Model Standardowy, nie są w stanie wygenerować obserwowanej asymetrii barionowej z co najmniej dwóch po- wodów. Po pierwsze – przejścia fazowe pod wpływem odziaływań elektrosłabych nie są wy- starczająco silnymi przejściami pierwszego rodzaju, i dlatego asymetria barionowa tworzona w czasie przejścia fazowego rozmywa się następnie poprzez nietłumione procesy naruszające liczbę barionową w fazie ze złamaną symetrią. Po drugie, efekty łamania CP, związane z macierzą mieszania CKM, są za słabe aby wygenerować odpowiednią asymetrię barionową. Głównym celem rozprawy było zbadanie tych zagadnień w rozszerzeniach Modelu Standar- dowego z neutralnym zespolonym skalarem i parą dubletów izospinowych kwarków wektoro- wych (VQ). W tym celu wprowadziliśmy potencjał z miękką łamaną symetrią globalną U(1), stanowiący podstawę modelu Constrained SM+CS model (cSMCS). Gdy wartość oczekiwana dla zespolonego skalara jest niezerowa pojawia się możliwość spontanicznego łamania CP. Mieszanie zwykłych kwarków z Modelu Standardowego z kwarkami wektorowymi stanowi dodatkowe źródło łamania CP. Ten model prowadzi do przejścia fazowego silnie pierwszego rodzaju pod wpływem oddziaływań elektrosłabych i poprawnego opisu bariogenezy. Spek- trum cząstek skalarnych modelu cSMCS obejmuje trzy neutralne cząstki Higgsa, wśród nich przyjmuje się, że najlżejsza to cząstka Higgsa (SM-like) o własnościach zbliżonych do tych przewidywanych dla cząstki Higgsa z Modelu Standardowego i zaobserwowanych w roku 2012 w Large Hadron Collider (LHC, CERN, Genewa)) dla odkrytej cząstki Higgsa o masie ok. 125 GeV. W rozważanym modelu ta cząstka Higgsa pochodzi głównie z dubletu SU(2), z małą domieszką singletu. Obliczyliśmy również przekrój czynny na produkcję w LHC cząstek Higgsa z modelu cSMCS. Do opisu rozkładów kwarków i gluonów w protonach zastosowali- śmy rachunek zaburzeń Kwantowej Chromodynamiki (QCD) z dokładnością do wiodących logarytmów (LO QCD), używając nieprzecalkowanych rozkładów partonowych (the uninte- grated parton distribution functions (UPDF)), zaproponowanych przez Kimbera, Martina i 1 Ryskina (KMR). Najpierw przetestowaliśmy nasze podejście obliczając przekrój czynny na produkcję cząstki Higgsa z Modelu Standardowego i porównując nasze wyniki z innymi ist- niejącymi w literaturze oraz z danymi doświadczalnymi z doświadczeń ATLAS i CMS przy LHC. Po wykazaniu, że nasze obliczenia odtwarzają z wystarczającą dokładnością przewi- dywania teoretyczne i zgadzają się z danymi doświadczalnymi dla Modelu Standardowego, zastosowaliśmy nasze podejście do cząstek Higgsa z modelu cSMCS. Nasze przewidywania dla najlżejszej cząstki Higgsa jest oczywiście zbliżone do przewidywań dla cząstki z Modelu Standardowego, przewidywania dla cięższych cząstek Higgsa z modelu cSMCS dostarczają wskazówek do dalszych poszukiwań cząstek skalarnych. Badania rozszerzeń Modelu Stan- dardowego nie mogą się ograniczać jedynie do sektora Higgsa, gdyż efekty związane z ciemną materią (DM) obserwuje się zarówno w galaktykach, dużych strukturach Wszechświata, pro- mieniowaniu reliktowym (Cosmic Microwave Background Radiation) itp. Ponieważ żadna cząstka w modelu cSMCS nie nadaje się na cząstką ciemnej materii, wprowadziliśmy rozsze- rzenie tego modelu przez dodanie tzw. biernego dubletu SU(2) (the inert doublet) z zerową wartością próżniową. Taki model , nazwany przez nas cIDMS, ma założoną ścisłą syme- trię typu Z 2 i zawiera stabilną cząstkę ciemnej materii. Model opisuje poprawnie gęstość reliktową oraz wyniki pośredniej detekcji ciemnej materii jak również dane doświadczalne z LHC. Rozprawa zawiera również analizę modelu z dwoma dubletami pól skalarnych (Two Higgs Doublet Model (2HDM)) w oparciu o warunki kasowania się rozbieżności kwadrato- wych (Veltman conditions). Przeanalizowaliśmy wnioski wynikające z warunków Veltmana dla wersji tego modelu z miękkim łamaniem symetrii Z 2 , próżnią typu mieszanego (Mixed Vacuum) , w które oba dublety mają niezerową wartość próżniową i oddziaływaniem Yukawy typu II. Z założenia symetria CP jest zachowana w rozważanym modelu. Spektrum cząstek skalarnych w tym modelu zawiera trzy cząstki neutralne h , H i A oraz dwie naładowane H + , H − . Zarówno h jak i cięższa od niej cząstka H mogą odgrywać rolę cząstki Higgsa z Modelu Standardowego. Przeanalizowaliśmy dwa możliwe scenariusze typu ŚM-like"dla cząstki h i cząstki H , uwzględniając najnowsze dane z LHC dotyczące masy ( ∼ 125 GeV) i sprzężeń do bozonów cechowania cząstki Higgsa oraz inne ograniczenia, w tym na masę naładowanego bozonu Higgsa H + , z rozpadu kwarku b. Wykazaliśmy, że warunki Veltmana są spełnione jedynie dla cząstki h i uzyskaliśmy zbieżność naszych przewidywań dla parame- trów modelu z najlepszym dopasowaniem uzyskanym w LHC, zawierającym również pomiary niewykorzystywane w naszej analizie.
The Standard Model (SM) of particle physics is very successful, yet it leaves many basic questions unanswered. This thesis is focused on some of these open problems. The aim of this study is to explore and exploit the origins of the matter-antimatter asymmetry in the Universe and the origins of dark matter (DM). Baryogenesis, the creation of the baryon asymmetry in the Universe, is a long-standing problem in cosmology. Sakharov formulated his well-known conditions for baryogenesis: baryon number violation, C and CP violation, and a departure from thermal equilibrium. Among the many particle physics scenarios that have been proposed in the past decades, electroweak baryogenesis is interesting. It has become apparent that the SM of electroweak interactions is unable to account for the observed magnitude of the BAU for at least two reasons. Firstly, the electroweak phase transition is not strongly first-order and therefore, any baryon asymmetry created during the transition would subsequently be washed out by unsuppressed baryon violating processes in the broken phase. Secondly, there is not enough CP violation from the CKM matrix to generate the baryon asymmetry. With the motivation of investigating these problems, we extend the SM by a neutral complex scalar singlet, and a pair of heavy iso-doublet vector quarks (VQ). We consider the potential with a softly broken global U(1) symmetry, which we call the Constrained SM+CS model (cSMCS). Assuming nonzero vacuum expectation value for the complex singlet, we analyze the physical conditions for spontaneous CP violation. The mixing of SM quarks with heavy VQ pairs result in the appearance of additional CP violation. This model provides the strong enough first order EW phase transition and leads to a proper description of baryogenesis. The scalar spectrum of the cSMCS includes three neutral Higgs particles with the lightest one considered to be the 125 GeV SM-like Higgs boson found in 2012 at the LHC. In the considered model, the SM-like Higgs boson comes mostly from the SM-like SU(2) doublet, with a small correction from the singlet. We present a prediction of the production rates of the cSMCS model Higgs bosons at the LHC, using a conventional effective LO QCD framework and the unintegrated parton distri- bution functions (UPDF) of Kimber-Martin-Ryskin (KMR). We first compute the SM Higgs production cross-section and compare the results to the existing calculations from different frameworks as well as to the experimental data from the CMS and ATLAS collaborations. It is shown that our framework is capable of producing sound predictions in this case. The- refore we use it for calculation of the cSMCS predictions for the Higgs boson production at the LHC. These predictions for yet undetected Higgs bosons of the cSMCS model may provide some clues for the future discovery. On the other hand, the gravitational effects of DM have been observed in galaxies, clusters of galaxies, the large-scale structure of the Universe and the Cosmic Microwave Background Radiation. Since none of the particles in the cSMCS model satisfies these conditions, we introduce, in addition a SU(2) doublet with zero vacuum expectation value (The Inert Do- ublet). This model, that we call cIDMS has an exact Z 2 symmetry and provides correct relic density of DM while fulfilling direct and indirect DM detection limits and simultaneously agree with the LHC results. The last part of this thesis is devoted to the applying Veltman condition in the Two Higgs Double Model (2HDM) in order to find the masses of the heavy scalars. The 2HDM is one of the simplest extensions of the SM, providing rich phenomenology. It contains an extended scalar sector which instead of one complex SU (2) doublet presence in the SM contains two of the doublets, with weak hypercharges equal to 1 . We analyze the soft Z 2 symmetry breaking version of the 2HDM with non-zero vacuum expectation values for both Higgs doublets (Mixed vacuum). We assume that CP is conserved in the scalar sector. In the particle spectrum of this model, there are two neutral CP-even scalars h and H , h being lighter than H . These scalars are two possible candidates for the SM-like Higgs boson, forming two possible scenarios. In the model, there are also a CP-even scalar (pseudoscalar) A and the charged Higgs bosons H ± . The results are constrained by comparing the properties of the light Higgs particle with the corresponding LHC data. We have found that the consistent solution exists only for the SM-like h scenario, with properties in agreement with the recent experimental data

Dissertação de Mestrado em Física apresentada à Faculdade de Ciências e Tecnologia
No Modelo Padrão (SM), é previsto que o bosão de Higgs seja uma partícula escalar e que suas interações não violem a simetria CP. Após a observação da produção do bosão de Higgs em associação com um par de quarks top (ttH) pelas experiências ATLAS e CMS em 2018, a observação de uma componente ímpar à transformações de carga-paridade (CP) em um dos acoplamentos do bosão de Higgs constituiria uma importante descoberta de física além do SM (BSM). Recentemente, ATLAS e CMS procuraram essa componente em eventos ttH com o Higgs decaindo em dois fotões. No entanto, o acoplamento entre o Higgs e os fotões é induzido por loops e pode ser afetado por efeitos da nova física. Esta tese descreve o estudo da natureza CP do acoplamento de Yukawa do Higgs aos quarks top por meio da análise de eventos ttH no canal de decaimento H→bb, e fornece projeções deste estudo do Run 2 do Large Hadron Collider (LHC) ao LHC de alta luminosidade (HL-LHC). A análise usa dados de colisão protão-protão coletados com o detector ATLAS durante o período do Run 2 do Grande Colisor de Hadrões (LHC) com uma energia de centro de massa de √s=13 TeV e luminosidade integrada total de 139 fb-1. São usados apenas eventos contendo um ou dois leptões no estado final do decaimento do par de quarks top. Em seguida, os eventos são classificados em regiões de acordo com o número de jatos e o número de b-jatos marcados usando ponto de operação (WPs) de 60% and 70%. Várias técnicas multivariadas foram usadas para melhorar a sensibilidade da análise, uma árvore da decisão reforçada (BDT) foi treinada para separar o sinal do fundo e outra para distinguir entre diferentes cenários de CP. Variáveis sensíveis ao CP, incluindo observáveis calculadas no referencial de laboratório e variáveis angulares calculadas em referenciais específicos, foram usadas no ajuste e no treinamento das BDTs.Um ajuste de verossimilhança é executado em todas as regiões de análise para restringir as previsões de fundo e reduzir as incertezas sistemáticas. O valor esperado para o ângulo de mistura CP é obtido desse ajuste. Além disso, uma extrapolação da análise foi realizada nesta tese, a fim de fornecer projeções sobre a medição do ângulo de mistura de CP para o LHC de alta luminosidade (HL-LHC). Foram considerados diferentes cenários para a evolução das incertezas sistemáticas com o aumento esperado da luminosidade. O valor esperado para o ângulo de mistura de CP foi obtido para vários valores diferentes de luminosidade até 3000 fb-1. Com as atuais incertezas sistemáticas, espera-se que a produção de ttH pura CP-ímpar seja excluída com 99.73\% de nível de confiança (CL) apenas no final do projeto HL-LHC. A significância de exclusão CP-ímpar é representada em função da luminosidade para cada um dos cenários considerados, e os efeitos dos vários tipos de incertezas são avaliados.
In the Standard Model (SM), the Higgs boson is predicted to be a scalar particle with no CP-violating interactions. After the observation of the Higgs boson production in association with a top quark pair (ttH) by ATLAS and CMS in 2018, the measurement of an odd charge-parity (CP) component in one of the Higgs boson couplings would constitute an important discovery of physics beyond the SM (BSM). Recently, ATLAS and CMS searched for such a component in ttH events with the Higgs decaying into two photons. However, the coupling between the Higgs and the photons is loop-induced and could be modified by effects of new physics. This thesis describes the study of the CP nature of the Higgs Yukawa coupling to the top quarks by analyzing ttH events in the H→bb decay channel, and provides projections of this search from the Large Hadron Collider (LHC) Run 2 to the High-Luminosity LHC (HL-LHC). The analysis uses the full Run 2 dataset of proton-proton collision collected with the ATLAS detector at a center-of-mass energy of √s=13 TeV and total integrated luminosity of 139 fb-1. Only events containing either one or two leptons in the final state from the decay of the top quark pair are used in the analysis. Then, the events are classified into regions according to the number of jets and the number of b-tagged jets using the 60% and 70% working points (WPs). Two sets of multivariate classifiers are utilized to improve the analysis sensitivity. One classifier targets the classification of signal against backgrounds and the other targets the separation between different CP scenarios. Several CP sensitive variables, including lab-frame observables and angular variables calculated in specific frames, were used in the training of the BDTs. A profile likelihood fit is performed over all analysis regions to constrain the background predictions and reduce the systematic uncertainties. The expected value for the CP-mixing angle is presented. An extrapolation of the analysis is performed in order to provide projections on the measurement of the CP-mixing angle for the HL-LHC. Different scenarios for the evolution of the systematic uncertainties with the expected increase in the luminosity were considered. The expected value for the CP-mixing angle was obtained for several different values of luminosity up to 3000 fb-1. With the current systematic uncertainties, the pure CP-odd ttH production is expected to be excluded with 99.73% confidence level (CL) only at the end of the HL-LHC project. The CP-odd exclusion significance is represented as a function of the luminosity for each of the scenarios considered, and the effects of the various types of uncertainties are evaluated.
Outro - FCT CERN/FIS-PAR/0002/2019

Tese de mestrado, Física (Física Nuclear e Partículas) Universidade de Lisboa, Faculdade de Ciências, 2020
The matter-antimatter asymmetry observed in the Universe cannot be explained by the amount of violation of Charge Conjugation and Parity (CP) in the Standard Model (SM). This shortcoming of the SM is one of the main motivations that led to the proposal of several extensions of the SM with new sources of CP-violation, a necessary requirement to explain the baryon asymmetry, according to the Sakharov conditions for baryogenesis. In this thesis, we will look at some of the main features of a particular type of models where the SM Higgs potential is changed by the addition of a second scalar doublet to the SM field content. These models are known as Two-Higgs-Doublet Models (2HDMs). They provide a very rich phenomenology at the Large Hadron Collider (LHC) and future colliders because of the introduction of new scalar states, and may answer many unsolved problems that are not addressed in the SM, such as the insufficiency of CP-violation and the existence of Dark Matter (DM). The CP-nature of the discovered Higgs is still an open issue. While it has been established by the ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid) collaborations that the discovered scalar cannot be a pure pseudoscalar, a mixed state with a large CP-odd component is still possible. This would be an indication of CP-violation in the scalar sector. The search for new sources of CP-violation and Beyond the Standard Model (BSM) physics is one of the main goals of the LHC. This can be achieved by a precise measurement of the Yukawa couplings since the CP-nature of the Higgs can be directly probed in its production alongside fermions. In this dissertation, we explore the sensitivity of CP-discrimination in the Higgs (h) couplings to bottom (b) and top quarks (t), for b ¯bh, bh and in dilepton final states of tth¯ events (with h → b ¯b) produced at the LHC and generated with MadGraph5 aMC@NLO. These Higgs bosons are generic, i.e., they may not correspond to the discovered one with a mass of 125 GeV, and are either pure CP-even or pure CP-odd. Several observables introduced in previous works are evaluated for a varying scalar boson mass, mh, in order to probe the CP-sensitivity in the different processes. We show that for b ¯bh and bh final states, CP-discrimination is not possible for the observables considered, even for very light Higgs masses of 10 GeV. For tth¯ , we found that distinguishing different CP states becomes increasingly difficult for larger masses, and seemingly impossible for masses above 450 GeV, at parton level. For the tops, we additionally apply an algorithm to reconstruct, for the first time, tth¯ events with a Higgs mass different from 125 GeV. Confidence Levels (CLs) for exclusion are computed for this process, as a function of the LHC luminosity, for different scenarios. We found that exclusion scenarios at the LHC require more luminosity for a fixed CL as we increase the scalar boson mass. CP-odd exclusion also requires more luminosity, relative to CP-even exclusion, for mh < 160 GeV. With the current LHC luminosity of 150 fb−1 , exclusion of a pure CP-even Higgs with a mass below 80 GeV, assuming SM-like couplings, is already possible. Also, the information that we may learn in these exclusion scenarios still leaves a large allowed parameter space for the Complex Two-Higgs-Doublet Model (C2HDM).