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Searching for hidden sector dark matter with fixed target neutrino experimentsdeNiverville, Patrick 30 August 2016 (has links)
We study the sensitivity of fixed target neutrino experiments (LSND, T2K, CENNS, and COHERENT) and proton beam dumps (MiniBooNE off-target, and SHiP) to sub-GeV dark matter. In order to reproduce the observed thermal relic abundance, these states are coupled to the Standard Model via new, low mass mediators in the form of a kinetically mixed U(1)0 vector mediator or a vector mediator gauging baryon number. We present a model for the production of low mass dark matter from proton-nucleon collisions in fixed targets. Sensitivity projections are made using signals from elastic electron- and nucleon-dark matter scattering, as well as coherent nuclear-dark matter scattering and dark matter induced inelastic π
0 production. A fixed target Monte Carlo code has been developed for this analysis, and documentation is included. We find that analyses using current and future proton fixed target experiments are capable of placing new limits on the hidden sector dark matter parameter space for dark matter masses of up to 500\,MeV and mediator masses as large as a few GeV. / Graduate
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Algumas consequências da SupergravidadeCosta, Ranieri Batista da 31 July 2015 (has links)
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Previous issue date: 2015-07-31 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Supersymmetry is a very useful tool for extending the Standard Model up to the
grand unification scale, studying electoweak symmetry breaking and providing dark matter
candidates. The presence of superpartners solves the problem of divergences, and changes
the renormalization group equations in a way that allows gauge coupling unification. In
a global supersymmetry the breaking scale is proportional to the vacuum energy, which
makes it incompatible with the low value of the cosmological constant. Promoting SUSY to
a local symmetry results in supergravity, which mandates existence of a spin-2 gravitational
field, naturally integrates General Relativity and particle physics, and is required to adjust
the potential and obtain a high breaking scale with low cosmological constant. This
review work looks into models based on gravity-mediated supersymmetry breaking. These
models allow a simpler hidden sector than their gauge-mediated or anomay-mediated
counterparts. And the lightest supersymmetric particles, higgsino-like, could be detected
once an electron-positron collider such as ILC is ready. / A supersimetria ´e uma ferramenta muito ´util para estender o Modelo Padr˜ao at´e a escala
de grande unifica¸c˜ao, para estudar a quebra de simetria eletrofraca e prover candidatos a
mat´eria escura. A presen¸ca dos superparceiros resolve o problema das divergˆencias, e altera
as equa¸c˜oes do grupo de renormaliza¸c˜ao de modo a permitir a unifica¸c˜ao dos acoplamentos
de gauge. A escala de quebra de uma supersimetria global ´e proporcional `a energia do
v´acuo, o que a tornaria incompat´ıvel com o baixo valor da constante cosmol´ogica. A
promo¸c˜ao de SUSY a uma simetria local resulta na supergravidade, que obriga a existˆencia
do campo gravitacional com spin-2, integra naturalmente a Relatividade Geral e a f´ısica
de part´ıculas, e ´e necess´aria para ajustar o potencial e obter alta escala de quebra com
constante cosmol´ogica baixa. Este trabalho de revis˜ao aborda modelos baseados na quebra
de supersimetria mediada por gravita¸c˜ao. Estes modelos aceitam um setor oculto mais
simples que os modelos concorrentes mediados por gauge ou por anomalias. E as part´ıculas
supersim´etricas mais leves, do tipo higgsino, podem ser detectadas quando um colisor
el´etron-p´ositron como o ILC estiver pronto.
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Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at the LHCChiu, Justin 22 December 2020 (has links)
This thesis presents the search for the dark sector process h -> Zd Zd -> 4l in events collected by the ATLAS detector at the Large Hadron Collider in 2015--2018. In this theorized process, the Standard Model Higgs boson (h) decays to four leptons via two intermediate Beyond-the-Standard-Model particles each called Zd. This process arises from interactions of the Standard Model with a dark sector. A dark sector consists of one or more new particles that have limited or zero interaction with the Standard Model, such as the new vector boson Zd (dark photon). It could have a rich and interesting phenomenology like the visible sector (the Standard Model) and could naturally address many outstanding problems in particle physics. For example, it could contain a particle candidate for dark matter. In particular, Higgs decays to Beyond-the-Standard-Model particles are well-motivated theoretically and are not tightly constrained; current measurements of Standard Model Higgs properties permit the fraction of such decays to be as high as approximately 30%. The results of this search do not show evidence for the existence of the h -> Zd Zd -> 4l process and are therefore interpreted in terms of upper limits on the branching ratio B(h -> Zd Zd) and the effective Higgs mixing parameter kappa^prime. / Graduate
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