Física (Mag.)
URI permanente para esta colecciónhttp://54.81.141.168/handle/123456789/9081
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Ítem Texto completo enlazado Recasting and Validating a Search for Long Lived Particles using a CalRatio trigger in the ATLAS experiment(Pontificia Universidad Católica del Perú, 2023-09-22) Coll Saravia, Lucía Ximena; Jones Pérez, JoelThe Standard Model (SM) of particle physics consists in a description of all the known elementary particles and their interactions. As far as it is known, the SM has passed all experimental tests, but presents some imperfections having no explanation for such as the presence of neutrino masses and the hierarchy problem. This encourages to probe theories beyond the Standard Model (BSM) that could bring solutions to these problems. An interesting proposal is to search for neutral long lived particles (LLPs). These type of particles have long decay lengths, can be generated by a variety of BSM models and could be detected in collider experiments by searching for displaced signals. The detection of the decay products of LLPs decays will contribute to the discovery of new physics. The objective of this work is to upgrade and optimize the PUCP Toy Detector presented in [1], adapting the simulation to the ATLAS detector and adding new features as a Geant4 simulation of the calorimeter for calculating the energy deposits. And validating it by reproducing the result of the searches presented in [2]. We conclude that the PUCP Toy Detector is valid, well implemented, and will be a competitive tool for searching new models containing LLPs decaying inside the calorimeters in the future.Ítem Texto completo enlazado Estudio de cortes cinemáticos en la búsqueda de física nueva en el LHC(Pontificia Universidad Católica del Perú, 2018-07-09) Silva Malpartida, Yolvi Javier; Jones Pérez, JoelUno de los retos más importantes en la búsqueda de física nueva, en los procesos del LHC, es reducir el “Ruido de fondo". En este trabajo, se buscará reducir el “Ruido de fondo" de algunos procesos del Modelo Estándar como la producción de pp ---> tt + jets, pp ---> W + jets, pp ---> Z + jets (Z---> vv ) y multijets (pp ---> jets), con un conjunto de cortes cinemáticos a variables usados en el experimento CMS. Para este propósito se empleará software avanzado como Pythia y Delphes.Ítem Texto completo enlazado Majorana vs Pseudo-Dirac Neutrinos at the ILC(Pontificia Universidad Católica del Perú, 2018-06-21) Suarez Navarro, Omar Giancarlo; Jones Pérez, JoelModelos Seesaw de masas de neutrinos a baja escala con una simetría aproximada de número leptónico pueden ser probados en colisionadores. En el modelo mínimo Seesaw Tipo I, implica la existencia de dos fermiones de Majorana pesados altamente degenerados que forman un par Pseudo-Dirac. Una pregunta muy importante es, en qué medida los futuros colisionadores tendrán sensibilidad al splitting entre los componentes de Majorana de este lepton pesado neutro, que señala la ruptura de número leptónico. Consideramos la producción de estos leptones pesados en la ILC, donde sus displaced decays proporcionan una señal de oro: una asimetría forward-backward, que depende crucialmente del splitting de la masa entre los dos componentes de Majorana. Mostramos que este observable puede limitar el splitting de la masa a valores mucho m´as bajos que los límites actuales, que provienen del neutrinoless double beta decay y las loop corrections.Ítem Texto completo enlazado Constraining sleptons at the LHC in a supersymmetric low-scale seesaw scenario(Pontificia Universidad Católica del Perú, 2017-06-28) Cerna Velazco, Nhell Heder; Jones Pérez, JoelThe discovery of the Higgs boson in the 8 TeV run of the LHC [1, 2] marks one of the most important milestones in particle physics. Its mass is already known rather precisely: mh = 125.09 ± 0.21 (stat.) ±0.11 (syst.) GeV [3], and the signal strength of various LHC searches has been found consistent with the SM predictions. While this completes the Standard Model (SM) particle-wise, several questions still remain open, for example: (i) Is it possible to include the SM in a grand unified theory where all gauge forces unify? (ii) Is there a particle physics explanation of the observed dark matter relic density? (iii) What causes the hierarchy in the fermion mass spectrum and why are neutrinos so much lighter than the other fermions? What causes the observed mixing patterns in the fermion sector? (iv) What stabilizes the Higgs mass at the electroweak scale? Supersymmetric model address several of these questions and consequently the search for supersymmetry (SUSY) is among the main priorities of the LHC collaborations. Up to now no significant sign for physics beyond SM has been found. The combination of the Higgs discovery with the (yet) unsuccessful searches has led to the introduction of a model class called ‘natural SUSY’ [4–15]. Here, the basic idea is to give electroweak-scale masses only to those SUSY particles giving a sizeable contribution to the mass of the Higgs boson, such that a too large tuning of parameters is avoided. All other particle masses are taken at the multi-TeV scale. In particular, masses of the order of a few hundred GeV up to about one TeV are assigned to the higgsinos (the partners of the Higgs bosons), the lightest stop (the partner of the top-quark) and, if the latter is mainly a left-stop, also to the light sbottom In addition the gluino and the heavier stop masses should also be close to at most a few TeV. Neutrino oscillation experiments confirm that at least two neutrinos have a non-zero mass. The exact mass generation mechanism for these particles is unknown, and both the SM and the MSSM remain agnostic on this topic. Although many ways to generate neutrino mass exist, perhaps the most popular one is the seesaw mechanism [16–21]. The main problem with the usual seesaw mechanisms lies on the difficulty in testing its validity. In general, if Yukawa couplings are sizeable, the seesaw relations require Majorana neutrino masses to be very large, such that the new heavy states cannot be produced at colliders. In contrast, if one requires the masses to be light, then the Yukawas need to be small, making production cross-sections and decay rates to vanish. A possible way out of this dilemma lies on what 3 is called the inverse seesaw [22], which is based on having specific structures on the mass matrix (generally motivated by symmetry arguments) to generate small neutrino masses. This, at the same time, allows Yukawa couplings to be large, and sterile masses to be light. We consider here a supersymmetric model where neutrino data are explained via a minimal inverse seesaw scenario where the gauge-singlet neutrinos have masses in the range O(keV) to O(100 GeV). We explore this with a parametrization built for the standard seesaw, and go to the limit where the inverse seesaw emerges, such that Yukawas and mixings become sizeable. Although non-SUSY versions of this scenario can solve the dark matter and matter-antimatter asymmetry problems [23–25], we shall make no claim on these issues in our model. In view of the naturalness arguments, we further assume that the higgsinos have masses of O(100 GeV), whereas the gaugino masses lie at the multi-TeV scale (see [26] for an example of such a scenario). In addition, we assume all squarks are heavy enough such that LHC bounds are avoided, and play no role in the phenomenology within this work1. In contrast we allow for fairly light sleptons and investigate the extent to which current LHC data can constrain such scenarios. This paper is organized as follows: in the next section we present the model. Section III summarizes the numerical tools used and gives an overview of the LHC analysis used for these investigations. In Section IV we present our findings for the two generic scenarios which differ in the nature of the lighest supersymmetric particle (LSP): a Higgsino LSP and a sneutrino LSP. In Section V we draw our conclusions. Appendices A and B give the complete formulae for the neutrino and sneutrino masses.Ítem Texto completo enlazado Symmetry breaking in grand unified theories(Pontificia Universidad Católica del Perú, 2016-04-14) Torrejón Maguiña, Miguel Ángel; Jones Pérez, JoelIn this work we review the symmetry breaking mechanism of gauge theories. On the first chapters of this thesis, we review the concept of symmetry as the action of a group that leaves an object invariant, in particular Lagrangians and actions, and then develop the corresponding globally and gauge symmetric theories and the relationship between them. It also reviewed the concept and general framework of the spontaneous breaking of a symmetry for renormalizable potentials. Correspondingly, two main results for global symmetries, Noether’s theorem and Goldstone’s Theorem, are reviewed in a general setting. Chapter 3 is the most important part of this work. The Brout-Englert-Higgs mechanism is explained and used to retrieve the symmetry breaking patterns for the vector and all the second rank tensor irreducible representations of the O(n) and SU(n) groups. In general we will retrieve the vacuum expectation value (vev) for the particular representation and value of the parameters of the potential. Then, for this vev, we calculate the number of massive vector bosons of the theory. Following BEH mechanism and Goldstone’s theorem, this number is equal to the number of broken generators delining thus the particular symmetry breaking pattern. Chapter 4 is a review of the Standard Model with an aim towards Grand Unified Theories (GUTs). Lastly in Chapter 5 we review the group theory of the minimal model SU(5) in a very exhaustive way and use the results of Chapter 3 to see the breaking patterns for this particular GUT.