Measurements of the inclusive isolated-photon and photon-plus-jet production in pp collisions at √s = 13 TeV with the ATLAS detector

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de Lectura: 10-12-2021This thesis presents various measurements of the di˙erential cross section for isolatedphoton production inclusively and in association with one jet in proton-proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. These measurements are sensitive to the parton distribution functions in the proton. In addition, a study of the in situ calibration of the jet energy scale and resolution of jets using photonplus-jet events in proton-proton collisions at a centre-of-mass energy of 13 TeV is also included. The inclusive isolated-photon di˙erential cross section was measured using a sample of events corresponding to an integrated luminosity of 36.1 fb−1 collected during the 2015 and 2016 data-taking periods. The measurement was performed in four di˙erent regions of the pseudorapidity of the photon as a function of the photon transverse energy. A later measurement was performed using the full integrated luminosity of the ATLAS Run II data of 139 fb−1 , increasing the regions of pseudorapidity of the photon from four to six and measuring the cross section for two di˙erent photon isolation cone sizes. In both measurements, theoretical predictions are found to provide a good description of the data within the experimental and theoretical uncertainties. The production of isolated-prompt photons associated with one jet was studied using 138.4 fb−1 of the ATLAS Run II dataset. The di˙erential cross section was measured as a function of the transverse energy of the photon for di˙erent angular con˝gurations of the photon and the jet. The next-to-leading order perturbative QCD calculations describe adequately the data. The jet energy scale and resolution were measured using in situ techniques in photonplus-jet events in which the photon and the leading jet transverse momenta are balanced. The jet energy scale (resolution) measurement presented in this dissertation was performed using a sample of events corresponding to an integrated luminosity of 80 fb−1 (58.5 fb−1) collected during the 2015 − 2017 (2018) data-taking periods. The in situ γ+jet corrections to the jet energy scale are at the level of 2% in most of the measured range of the photon transverse momentum, and the uncertainty on the jet energy scale is of the order of 1% for the di˙erent measured con˝gurations. Resolutions at the order of 17% − 24% (4% − 5%) with experimental uncertainties of ≈ 25% − 45% (≈ 35%) are obtained at photon transverse momenta of 25−45 GeV (≈ 1.2 TeV) for the two measured regions of jet rapidity and jet collection

Precision measurements of jet and photon production at ATLAS

The production of jets and prompt isolated photons at hadron colliders provides stringent tests of perturbative QCD. The latest measurements performed by the ATLAS Collaboration at the LHC are presented in these proceedings. The inclusive prompt-photon production is measured for two distinct photon isolation cones, $R = 0.2$ and $0.4$, as well as for their ratio. This measurement is sensitive to the gluon parton density distribution in the proton. In addition, a measurement of variables probing the properties of the multijet energy flow which are used to determine the strong coupling constant is presented. These measurements are compared to state-of-the-art NLO and NNLO predictions. Lastly, a measurement of new event-shape jet observables defined in terms of reference geometries with cylindrical and circular symmetries using the energy mover's distance is discussed.Comment: DIS202

Estudio de la estructura de la parte bosónica de la supergravedad en D=11

The aim of this degree project is based on the study of supergravity in D= 11. We analize the possible connexion of supergravity with a Chern-Simons theory based on the group Osp (1/32). To this end, we will only consider the bosonic case (i.e. we will take the gravitino field equal to zero) and we will build a CS theory modified with a field given by a 3-form A. After completing this procedure we will compare the field equations of both models and observe that our CS theory reproduce the equations of supergravity in D= 11 for some selection of the parameters. Then, the role of the auxiliary field is played by the gauge fields of certain Osp (1/32) generators, that would provide evidence supporting the existence of a relation between supergravity in D= 11 with a CS theory.Grado en Físic

Search for flavour-changing neutral-current interactions of a top quark and a gluon in pp collisions at √s = 13 TeV with the ATLAS detector

A search is presented for the production of a single top quark via left-handed flavour-changing neutralcurrent (FCNC) interactions of a top quark, a gluon and an up or charm quark. Two production processes are considered: u + g → t and c + g → t. The analysis is based on proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of 139 fb−1. Events with exactly one electron or muon, exactly one b-tagged jet and missing transverse momentum are selected, resembling the decay products of a singly produced top quark. Neural networks based on kinematic variables differentiate between events from the two signal processes and events from background processes. The measured data are consistent with the background-only hypothesis, and limits are set on the production cross-sections of the signal processes: σ (u + g → t) × B(t → W b) × B(W → ν) < 3.0 pb and σ (c + g → t)×B(t → W b)×B(W → ν) < 4.7 pb at the 95% confidence level, with B(W → ν) = 0.325 being the sum of branching ratios of all three leptonic decay modes of the W boson. Based on the framework of an effective field theory, the cross-section limits are translated into limits on the strengths of the tug and tcg couplings occurring in the theory: |C ut uG|/ 2 < 0.057 TeV−2 and |C ct uG|/ 2 < 0.14 TeV−2. These bounds correspond to limits on the branching ratios of FCNC-induced top-quark decays: B(t → u + g) < 0.61 × 10−4 and B(t → c + g) < 3.7 × 10−

Operation and performance of the ATLAS semiconductor tracker in LHC Run 2

Artículo escrito por un elevado número de autores, solo se referencia el que aparece en primer lugar, el nombre del grupo de colaboración, si lo hubiere, y los autores pertenecientes a la UAMThe semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector. It consists of 4088 silicon strip sensor modules. During Run 2 (2015–2018) the Large Hadron Collider delivered an integrated luminosity of 156 fb-1 to the ATLAS experiment at a centre-of-mass proton-proton collision energy of 13 TeV. The instantaneous luminosity and pile-up conditions were far in excess of those assumed in the original design of the SCT detector. Due to improvements to the data acquisition system, the SCT operated stably throughout Run 2. It was available for 99.9% of the integrated luminosity and achieved a data-quality efficiency of 99.85%. Detailed studies have been made of the leakage current in SCT modules and the evolution of the full depletion voltage, which are used to study the impact of radiation damage to the module

A search for the Zγ decay mode of the Higgs boson in pp collisions at √s = 13 TeV with the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Search for dark matter in association with an energetic photon in pp collisions at √s = 13 TeV with the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMA search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at √s = 13 TeV. The data, collected during 2015–2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb−1. No deviations from the predictions of the Standard Model are observed and 95% confidence-level upper limits between 2.45 fb and 0.5 fb are set on the visible cross section for contributions from physics beyond the Standard Model, in different ranges of the missing transverse momentum. The results are interpreted as 95% confidence-level limits in models where weakly interacting dark-matter candidates are pair-produced via an s-channel axial-vector or vector mediator. Dark-matter candidates with masses up to 415 (580) GeV are excluded for axial-vector (vector) mediators, while the maximum excluded mass of the mediator is 1460 (1470) GeV. In addition, the results are expressed in terms of 95% confidence-level limits on the parameters of a model with an axion-like particle produced in association with a photon, and are used to constrain the coupling gaZγ of an axion-like particle to the electroweak gauge boson