ATLAS Electron and Photon Trigger

ATLAS electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential to record signals for a wide variety of physics: from the Standard Model processes to searches for new phenomena. To cope with ever-increasing luminosity and more challenging pile-up conditions at a centre-of-mass energy of 13 TeV, the trigger selections need to be optimized to control the rates and keep efficiencies high. The ATLAS electron and photon trigger in Run-2 is presented, including new techniques developed to maintain their high performance even in high pile-up conditions as well as the first efficiency measurements from the 2018 data taking.Instituto de Física La PlataConsejo Nacional de Investigaciones Científicas y Técnica

Búsqueda de supersimetría en el detector ATLAS (CERN-LHC)

La búsqueda de nueva física más allá del Modelo Estándar es el principal objetivo de la física experimental de altas energías desde el descubrimiento del bosón de Higgs por ATLAS y CMS en 2012. Motivaciones relacionadas con mediciones astrofísicas que predicen la existencia de materia y energía oscura, o el supuesto de una gran unificación de las fuerzas elementales de la naturaleza, entre tantas otras, justifican dicha búsqueda. La Supersimetría (SUSY) es la teoría mejor fundamentada desde el punto de vista teórico y provee modelos con estados finales atractivos para su búsqueda en colisionadores como el LHC. En esta tesis se presenta un estudio para la búsqueda de nueva física en el marco de la teoría SUSY en estados finales con fotones aislados, jets y alto momento transversal faltante en colisiones protón-protón a una energía de centro de masa de 13 TeV. La búsqueda se realiza utilizando el conjunto de datos colectados con el detector ATLAS en el LHC entre 2015 y 2018, correspondiente a una luminosidad integrada de 139 f b −1 . Para un correcto análisis de los datos es imprescindible estudiar las eficiencias de selección de objetos a medida que se adquieren datos. En este contexto, esta tesis presenta un estudio detallado del cálculo de las eficiencias del trigger de fotones y de multijets. Se presenta además un estudio de factibilidad para una búsqueda en el marco de un modelo de SUSY más complejo, conocido como Stealth SUSY, con fotones, múltiples jets y bajo momento transverso faltante en el estado final.The search for new physics beyond the Standard Model is the main objective of experimental high energy physics since the discovery of the Higgs boson by ATLAS and CMS in 2012. Motivations related to astrophysical measurements that predict the existence of matter and dark energy, or the assumption of a great unification of the elemental forces of nature, among many others, justify this search. Supersym- metry (SUSY) is the theory best motivated from the theoretical point of view and provides models with attractive final states for their search in colliders such as the LHC. In this thesis a study for the search of new physics within the framework of the SUSY theory in final states with isolated photons, jets and high missing transverse momen- tum in proton-proton collisions at a center of mass energy of 13 TeV, is presented. The search is performed using the dataset collected with the ATLAS detector at the LHC between 2015 and 2018, corresponding to an integrated luminosity of 139 f b −1 . For a correct analysis of the data it is essential to study the efficiencies of the object selection as data is acquired. In this context, this thesis presents a detailed study of the calculation of photon and multijet trigger efficiencies. A feasibility study is also presented for a search within the framework of a more complex SUSY model, known as Stealth SUSY, with photons, multiple jets and low missing transverse momentum in the final state.Facultad de Ciencias Exacta

Measurement of the prompt J/ψ pair production cross-section in pp collisions at √s = 8 TeV with the ATLAS detector

The production of two prompt J/ψ mesons, each with transverse momenta pT > 8.5 GeV and rapidity |y| −1 collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised J/ψ production, is measured as a function of the transverse momentum of the lower-pT J/ψ meson, di-J/ψ pT and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthal angle between the two J/ψ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two J/ψ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be σeff = 6.3 ± 1.6 (stat) ± 1.0 (syst) mb.Facultad de Ciencias Exacta

High-ET isolated-photon plus jets production in pp collisions at √s=8 TeV with the ATLAS detector

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Física La Plat

Measurement of the cross section for inclusive isolated-photon production in pp collisions at √s = 13 TeV using the ATLAS detector

Inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV is studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 3.2 fb−1. The cross section is measured as a function of the photon transverse energy above 125 GeV in different regions of photon pseudorapidity. Next-to-leading-order perturbative QCD and Monte Carlo event-generator predictions are compared to the cross-section measurements and provide an adequate description of the data.Facultad de Ciencias Exacta

Search for doubly charged scalar bosons decaying into same-sign W boson pairs with the ATLAS detector

A search for doubly charged scalar bosons decaying into W boson pairs is presented. It uses a data sample from proton–proton collisions corresponding to an integrated luminosity of 36.1 fb−1 collected by the ATLAS detector at the LHC at a centre-of-mass energy of 13 TeV in 2015 and 2016. This search is guided by a model that includes an extension of the Higgs sector through a scalar triplet, leading to a rich phenomenology that includes doubly charged scalar bosons H±±. Those bosons are produced in pairs in proton–proton collisions and decay predominantly into electroweak gauge bosons H±± → W±W± . Experimental signatures with several leptons, missing transverse energy and jets are explored. No significant deviations from the Standard Model predictions are found. The parameter space of the benchmark model is excluded at 95% confidence level for H±± bosons with masses between 200 and 220 GeV.Facultad de Ciencias Exacta

High-ET isolated-photon plus jets production in pp collisions at √s=8 TeV with the ATLAS detector

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Física La Plat

Measurement of detector-corrected observables sensitive to the anomalous production of events with jets and large missing transverse momentum in pp collisions at √s=13 TeV using the ATLAS detector

Observables sensitive to the anomalous production of events containing hadronic jets and missing momentum in the plane transverse to the proton beams at the Large Hadron Collider are presented. The observables are defined as a ratio of cross sections, for events containing jets and large missing transverse momentum to events containing jets and a pair of charged leptons from the decay of a Z/γ∗ boson. This definition minimises experimental and theoretical systematic uncertainties in the measurements. This ratio is measured differentially with respect to a number of kinematic properties of the hadronic system in two phase-space regions; one inclusive single-jet region and one region sensitive to vector-boson-fusion topologies. The data are found to be in agreement with the Standard Model predictions and used to constrain a variety of theoretical models for dark-matter production, including simplified models, effective field theory models, and invisible decays of the Higgs boson. The measurements use 3.2 fb- 1of proton–proton collision data recorded by the ATLAS experiment at a centre-of-mass energy of 13 TeV and are fully corrected for detector effects, meaning that the data can be used to constrain new-physics models beyond those shown in this paper.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Física La Plat

Measurement of the cross section for inclusive isolated-photon production in pp collisions at √s = 13 TeV using the ATLAS detector

Inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV is studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 3.2 fb−1. The cross section is measured as a function of the photon transverse energy above 125 GeV in different regions of photon pseudorapidity. Next-to-leading-order perturbative QCD and Monte Carlo event-generator predictions are compared to the cross-section measurements and provide an adequate description of the data.Facultad de Ciencias Exacta

Measurement of detector-corrected observables sensitive to the anomalous production of events with jets and large missing transverse momentum in pp collisions at √s=13 TeV using the ATLAS detector

Observables sensitive to the anomalous production of events containing hadronic jets and missing momentum in the plane transverse to the proton beams at the Large Hadron Collider are presented. The observables are defined as a ratio of cross sections, for events containing jets and large missing transverse momentum to events containing jets and a pair of charged leptons from the decay of a Z/γ∗ boson. This definition minimises experimental and theoretical systematic uncertainties in the measurements. This ratio is measured differentially with respect to a number of kinematic properties of the hadronic system in two phase-space regions; one inclusive single-jet region and one region sensitive to vector-boson-fusion topologies. The data are found to be in agreement with the Standard Model predictions and used to constrain a variety of theoretical models for dark-matter production, including simplified models, effective field theory models, and invisible decays of the Higgs boson. The measurements use 3.2 fb- 1of proton–proton collision data recorded by the ATLAS experiment at a centre-of-mass energy of 13 TeV and are fully corrected for detector effects, meaning that the data can be used to constrain new-physics models beyond those shown in this paper.La lista completa de autores que integran el documento puede consultarse en el archivoInstituto de Física La Plat