Die Arbeit beschreibt die Messung des Wirkungsquerschnittes für die Produktion von Jets in Ereignissen mit Z-Bosonen in Proton-Proton Kollisionen bei einer Schwerpunktsenergie von √s = 7 TeV mit einer integrierten Luminosität von ∫Ldt = 36 pb−1 und ∫Ldt = 4.6 fb−1 aufgenommen mit dem ATLAS Experiment am Large Hadron Collider in Genf. Die inklusiven und differenziellen Wirkungsquerschnitte für Z (→ e+ e−) + jets werden für Jets mit einem Transversalimpuls von pT(jet) > 30 GeV und einer Rapidität von |y(jet)| < 4.4 gemessen. Die Datensätze erlauben Messungen in vorher nicht zugänglichen Phasenraumregionen und können genutzt werden, um die Modellierungen von Z/γ∗ + jets in typischen Phasenraumregionen, die vom Zerfall des Higgs Bosons oder Suchen nach neuer Physik erwarten werden, zu testen. Die Ergebnisse werden auf Partonlevel entfaltet und mit Vorhersagen verschiedener Monte-Carlo Generatoren und Vorhersagen der perturbativen QCD in nächst-führender Ordnung verglichen.

The biggest scientific experiment in history will begin taking data in late 2009 using the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. The LHC is designed to collide protons at an unprecedented 14 TeV centre of mass energy, enabling physicists to explore the constituents of matter at smaller scales than ever before. The Parton Distribution Functions (PDFs) are parametrizations of the proton structure and are best determined from experimental data. The PDFs are needed to calculate cross-sections or in other words the likelihood of observed physical processes, which are crucial in exploiting the discovery potential of the LHC. The prospects for measuring the Drell-Yan (DY) spectrum are assessed in the low invariant mass region below the Z boson resonance using e+e− pairs from the initial LHC data in order to probe the proton structure and further constrain the PDFs. The analysis is based on the full simulation of the ATLAS detector response to DY electrons and background processes. Assuming 100 pb−1 of LHC data, the total DY crosssection in the invariant mass range from 10 GeV to 60 GeV is expected to be measured as DY = 5.90±0.24(stat)±0.18(syst) nb. The result predicts an improvement over a current theoretical uncertainty of 7.6% and indicates that the PDF uncertainties can be reduced significantly with the early LHC data.

Detector mis-modelling or hardware problems may cause an excess of Missing Transverse Energy (MET) to be inferred in physics events recorded in ATLAS, leading to higher than expected backgrounds for new physics. In particular, non-Gaussian tails in the MET distribution are unlikely to be well modelled in Monte Carlo simulations. To account for this, a technique has been established to improve the background predictions derived from Monte Carlo simulations. This is done using a correction derived through comparison of control samples in data and Monte Carlo simulation. Two different control samples are used to create the correction, giving a range of predictions for the shape of the MET tail and aiding the calculation of systematic errors. This technique is then applied to several samples which are potential backgrounds to new physics which give detector signatures which include MET. / Graduate

Orientador: Prof. Dr. José Kenichi Mizukoshi / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2016. / Searches for new physics beyond the Standard Model are important subjects at the current Run-2 of the Large Hadron Collider (LHC) and next generation colliders. In this context, we make independent studies of the phenomenology of a new hypothetical heavy Majorana neutrino (N) and a heavy spin-1 charged vector (W¿) at the LHC and a future 100 TeV very large hadron collider (VLHC), we also study the potential of the future International Linear Collider (ILC) to measure the rare h ! Z Higgs decay. Toward this end, the N production via the W fusion process is investigated and found it to be larger than the Drell-Yan production for mN > 1 TeV at the 14 TeV LHC and for mN > 770 GeV at the 100 TeV VLHC. Then we computed the discovery potential of the these colliders to discover an N using the same-sign dimuon channel. In the case of the h ! Z Higgs decay we investigated the Higgsstrahlung production at the 250 GeV ILC, we found that a sensitivity of 58% can be reached in the inclusive ¿Ê¿Ê X channel with 3 ab.1, where X denotes the inclusive decay of the Z boson from the Higgs. Finally, in the case of the W¿, we studied its contribution to the h ! Higgs decay process and constrained the strength of the W¿W¿h interaction. Finally, we study the Drell-Yan W¿ production with its decay to the Wh pair at the LHC.

This PhD dissertation presents the measurement of the cross section of jet production in association with a Z boson in proton-proton collisions at the Large Hadron Collider in CERN, with a center-of-mass energy of 8 TeV in 2012 and of 13 TeV in 2015. The data used for this analysis were collected by the Compact Muon Solenoid (CMS) detector, with an integrated luminosity of 19.6 fb-1 in 2012 and of 2.25 fb-1 in 2015. The differential cross section is measured as a function of jet multiplicity, jet transverse momentum and rapidity, and the scalar sum of jet transverse momenta. The rapidity correlations between the Z boson and jets are also measured benefiting from the large statistics of data taken in 2012. All distributions of measured observables are obtained after correcting detector effects using unfolding approach, and the results of two leptonic decaying channels of Z boson are combined. Coming along with the systematic and statistical uncertainties, the measurement is compared to different theoretical predictions at different accuracy levels. The predictions are from MADGRAPH 5, SHERPA 2 (for 8 TeV analysis only), MADGRAPH_AMC@NLO, and fixed next-to-next-to-leading order (for 13 TeV analysis only). Thanks to the unprecedented high energy and the large statistics of data, precision measurement is accomplished in a physical phase space never reached before. This measurement provides precise systematics for different theoretical models. It also quantifies the improvement with higher order of perturbative quantum chromodynamics calculations on matrix elements relative to the leading order multi-leg approach. In particular to the rapidity correlation study, new matching schemes (FxFx and MEPS@NLO) for next-to-leading order matrix elements and parton shower show significant improvements with respect to the MLM matching scheme for leading order multi-leg matrix elements and parton shower. This measurement also gives precise background estimation for the measurements of many other processes in Standard Model like top quark production and gauge boson couplings, and for new physics searches such as Supersymmetry. In this thesis, the jet energy correction and calibration for the high level trigger system of CMS are also depicted. From 2012 to 2015, the Large Hadron Collider was upgraded, not only with the center-of-mass energy of the beams enlarged, but also with the instantaneous luminosity increased. The time distance between two particle bunches in a beam is reduced. As a result, the reconstructed momenta of the jets produced in each bunch crossing are significantly contaminated by multiple interactions. A dedicated technical approach has been developed for correcting the reconstructed jet momenta. The corrections have been calibrated and configured for the data taking in 2015 and 2016. / Cette thèse présente une mesure de la section efficace de production de jets associés à un boson Z dans les collisions proton-proton du Grand Collisionneur de Hadron (LHC) situé au CERN, avec des énergies dans le centre de masse de 8 TeV et 13 TeV, respectivement pour les années 2012 et 2015. Les données utilisées pour cette analyse ont été collectées par le détecteur Compact Muon Solenoid (CMS). Elles constituent des échantillons de luminosités intégrées de 19.6 fb⁻¹ et 2.25 fb⁻¹, respectivement pour 2012 et 2015. Nous mesurons la section efficace différentielle en fonction de la multiplicité de jets, de l’impulsion transverse et de la rapidité des jets, et en fonction de la somme scalaire des impulsions transverses des jets. La corrélation entre les rapidités du boson Z et des jets est aussi mesurée et bénéficie de la large statistique prise en 2012. Toutes les distributions d’observables mesurées sont obtenues après corrections pour les effets détecteurs et les résultats des canaux de désintégration muonique et électronique du boson Z sont combinés. Tenant compte des incertitudes statistiques et systématiques, les mesures sont comparées à différentes prédictions théoriques ayant différents niveaux de précision. Les prédictions sont obtenues de MADGRAPH 5, SHERPA 2 (pour l’analyse à 8 TeV uniquement), MADGRAPH_AMC@NLO, et un modèle fixé au NNLO (pour l’analyse à 13 TeV uniquement). Par ces mesures de précisions, et en particulier celle de la corrélation de rapidités, nous avons acquis une compréhension plus approfondie de la chromodynamique quantique dans son régime perturbatif. Grâce à la plus haute énergie jamais atteinte en laboratoire, et à la grande statistique disponible, nous avons sondé avec précision des endroits de l’espace des phases jusque là inaccessibles.Dans cette thèse, les corrections et la calibration de l’énergie des jets pour le haut niveau de sélection de CMS est également présentée. Durant la période de 2012 à 2015, le LHC a été amélioré, non seulement l’énergie dans le centre de masse a augmenté, mais la luminosité instantanée a aussi été amplifiée. L’écart temporelle entre deux paquets de particules dans les faisceaux du LHC a été réduite. L’une des conséquences est que l’impulsion reconstruite pour les jets produits lors d’un croisement de faisceau à une contribution significative venant des multiples interactions ayant lieux lors du croisement des paquets. Une approche technique dédiée a été développée pour corriger l'impulsion des jets. Les corrections obtenues ont été calibrées aux données prises en 2015 et 2016. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The Large Hadron Collider (LHC) is the most powerful and complex particle accelerator ever built. The ATLAS and the CMS are the two multipurpose particle detectors at the LHC, designed to cover a wide range of physics measurements. Three physics studies performed using data of proton-proton collisions collected with the ATLAS detector are presented. The identification of jets originating from b quarks, also known as b-tagging, is a crucial tool for many physics analyses at the LHC. This thesis presents a calibration of the b-tagging efficiency for high transverse momentum jets using a new calibration technique. This analysis is based on template fits and uses multi-jet events, which allows to perform the calibration for jets with transverse momenta up to 1200 GeV. This thesis also describes a completed and connected technical project on the development of the b-tagging ATLAS software. Dark Matter (DM) is a new phenomenon introduced to explain astrophysical observations. The nature of DM is one of the most important subjects of investigations in the modern physics, and many of these investigations are carried out at the LHC. A search for DM production in association with a pair of heavy flavour quarks has been recently performed in ATLAS at a centre-of-mass energy √s = 8 TeV under the Effective Field Theory approach. A re-interpretation of the results of this search under assumption of the simplified models is presented. A set of simplified models is considered with various DM masses, masses of the spin-0 exchange particle, that mediates the interaction between DM and the regular matter, and various values of couplings. Benchmark models are chosen to be used in the DM searches at √s = 13 TeV. The last part of the thesis presents a search for DM production in association with a pair of top quarks performed under assumption of the simplified models with spin-0 mediator, using the data collected at a centre-of-mass energy √s = 13 TeV. The observed data are shown to be in good agreement with the Standard Model predictions, and upper limits are set on a ratio between the observed DM production cross section and the value expected by the simplified model.

Orientador: José Augusto Chinellato / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-29T05:01:52Z (GMT). No. of bitstreams: 1 MedinaJaime_Miguel_D.pdf: 6686309 bytes, checksum: 48654e10cf1138cdc89eb810557a427d (MD5) Previous issue date: 2015 / Resumo: A produção exclusiva de bósons Z é um processo difrativo, teoricamente representado pela troca de um objeto com os números quânticos do vácuo (pomeron- IP), o qual pode ser tratado no modelo padrão no enfoque do mecanismo de dipolo, via fotoprodução. A caraterística principal deste tipo de processo é que os dois prótons emergem intactos após a colisão com momentum transverso pequeno. Assim, os prótons são espalhados muito frontais e escapam à detecção., restandonos como criterio de e. Espera-se , onde um próton irradia um fóton virtual, o qual flutua para um par quark anti-quark os quais são espalhados elasticamente pela troca de dois glúons emergentes do outro próton, e se materializa num bóson Z. Além disso, os dois prótons emergem intactos após a colisão com momentum transverso pequeno, assim prótons são espalhados muito frontais e escapam à detecção. Portanto, o critério usado para a identificação de eventos exclusivos de bósons Z decaindo em par múons é o número de traços adicionais no vértice, mas ainda resta a possibilidade de haver uma dissociação de pelo menos um dos prótons. Neste caso, a medida da seção de choque respectiva será contaminada. São expostos três diferentes métodos para a pré-seleção des eventos contendo eventos exclusivos. A estratégia de análise proposta para selecionar eventos exclusivos é baseada no decaimento de bósons Z em pares ???? caraterizados por grande momento transverso, para o qual exploramos múons em uma região cinemática de momento transverso Pt(?)>20 GeV, massa invariante M(????)>40 GeV/c² e pseudo-rapidez |?|<2,5. Adicionalmente a estes cortes, exigimos "zero traços" extras no vértice e, por último que o par de múons sejam back-to-back com balanço no Pt. Nesta Tese se apresenta um estudo da produção exclusiva de bósons Z em colisões próton-próton para energias de centro de massa igual a ?s=7 TeV no experimento CMS/LHC. Esta análise foi feita usando simulações para processos de Drell-Yan, fotoprodução de múons e dados coletados pelo detector CMS de colisões próton-próton com ?s=7 TeV durante o ano de 2011, correspondendo a uma luminosidade integrada de 5,09 fb?¹. Nenhum excesso significante de sinal foi extraído nas produções exclusivas de fazemos uma estimativa de eventos esperados nas produções exclusiva e bósons. Nenhum candidato a bóson Z exclusivo foi possível de observar, isto devido ao fato da baixa estatística e o enorme background proveniente de processos de Drell-Yan., que mesmo sendo processos não exclusivos contaminarem nossa amostra de dados devido ao fato de que os prótons escapam de nossa detecção e o único critério de exclusividade é o de o número de traços extras no vertice do evento seja igual a zero, mas devido a que os prótons podem dissociar sim ser detetados e nós foi impossível dete devido a que assim prótons são espalhados muito frontais e escapam à detecção. Entretanto, a seção de choque para processos de produção exclusiva de bósons Z é encontrada a ser ?excl(Z?????)<13,3 fb para um nível de confiança de 95%. Este é o primeiro resultado preliminar para este tipo de processo na escala de energia de 7 TeV, onde cabe destacar que este limite foi melhorado com respeito a resultados publicados pela colaboração CDF para ?s = 1,9 TeV / Abstract: he exclusive Z boson production is a diffractive process theoretically represented by the exchange of an object with the quantum numbers of vacuum (pomeron-IP), which is predicted by the Standard Model in the dipole mechanism approach, via photoproduction. The main feature of this type of process is two forward outgoing protons intact after the collision with small transverse momentum, the protons are scattering very front and escape detection. Then, the approach taken to detect exclusive Z bosons events decaying in to muon pair is the number of additional tracks on the vertex, but there is still the possibility of dissociation of at least one proton, then the measurement of cross section will be contaminated. It's exposed three different methods for the pre-selection events containing exclusive Z bosons. The strategy proposed to exclusive selection events, is based on the decay of Z bosons on pairs ???? featured by large transverse momentum, for which we explored muons in a kinematic region with transverse momentum Pt(?)>20 GeV, Invariant mass M(????)>40 GeV/c² and pseudorapidity |?|<2,5. The additional cuts, require zero extra tracks on vertex and finally the pair of muons are back-to-back with momentum transverse conservation . This thesis presents a search for exclusive Z boson production in proton proton collisions at ?s=7 TeV center of mass energy in the experiment CMS/LHC. This analysis was made using simulations to Drell-Yan processes, photoproduction of muon and data collected by the CMS detector on proton proton collisions with ?s=7 TeV in 2011, for 5.09 fb?¹ integrated luminosity record. No exclusive Z????? candidates are observed, because low statistical and huge background contribution from Drell-Yan processes. But even so, the cross section for the exclusive Z bosons production is found to be ?excl(Z?????)<13.3 fb at 95% C.L. This is the first very preliminary results for 7 TeV, where we highlight that it limit has been improved respect to the results published by the CDF collaboration to ?s = 1.9 TeV / Doutorado / Física / Doutor em Ciências / 147301/2011-04 / CNPQ

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A search for a heavy new particle Y decaying to a Standard Model Higgs boson H and another new particle X is presented. The search is performed using 139 fb−1 of p−p collision data at √s = 13 TeV recorded by the ATLAS detector. The H boson is identified through its decays to bb, with the only assumption applied to X being that it decays hadronically. The X is identified through a novel anomaly detection method via the use of a Variational Recurrent Neural Network trained directly on data collected by the ATLAS detector. This effort marks the first application of a fully unsupervised machine learning method to an ATLAS analysis. An additional benchmark based on interpreting the Y → XH process in the context of a heavy vector triplet model in which the X decays to two quarks defines an additional signal region in which upper limits on the HVT process cross section are reported at 95% confidence level.