Sterile neutrino searches in MINOS and MINOS+ experiments
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This dissertation presents the searches on sterile neutrinos using the data collected in MINOS+ Experiment from September 2013 to September 2014, and the full data set of MINOS Experiment collected from 2005 to 2012. Anomalies in short baseline experiments, such as LSND and MiniBooNE, showed hints of sterile neutrinos, a type of neutrino that does not interact with the Standard Model particles. In this work, two models are considered: 3+1 and large extra dimension (LED). In the 3+1 model, one sterile neutrino state is added into the standard oscillation scheme consisting of three known active neutrino states ν[subscript e], ν[subscript µ] and ν[subscript τ]. In the LED model, sterile neutrinos arise as Kaluza-Klein (KK) states due to assumed large extra dimensions. Mixing between sterile and active neutrino states may modify the oscillation patterns observed in the MINOS detectors. Both searches yield null results. For 3+1, a combined fit of MINOS and MINOS+ data gives a stronger limit on θ₂₄ in the range of 10⁻² eV² < ∆m²₄₃ < 1 eV² than previous experiments. For LED, with the complete MINOS data set, the size of extra dimensions is constrained to be smaller than ∼ 0.35 µm at 90% C.L. in the limit of a vanishing lightest neutrino mass.