A search for sterile neutrinos at the MINOS experiment
Robert Neil Pittam
MINOS is a long baseline neutrino oscillation experiment based at the Fermi National Accelerator Laboratory in Illinois, USA. The experiment was designed to study neutrino oscillation phenomena. The ν µ beam produced by the NuMI beam facility at FNAL is used along with two functionally identical detectors. The Near Detector at FNAL and a Far Detector 735 km away in the Soudan Underground Laboratory in northern Minnesota. Comparison of the observed spectra of neutrinos at the two detectors
... es the evidence for neutrino oscillations. This thesis presents work on the postulated phenomena of sterile neutrinos. Oscillations between active and sterile neutrinos will lead to a deficit in the expected rate of measured Neutral Current interactions at the Far Detector. A technique for selecting Neutral Current events utilising an Artificial Neural Network is presented with resulting overall efficiency of 91.1% and purity of 66.0%. A method of predicting the expected Charged and Neutral Current energy spectra at the Far Detector given the data recorded at the Near Detector is presented. A model to search for oscillations between sterile and active neutrinos is developed. Sources of systematic uncertainty that can effect the results of the analysis are discussed. The analysis developed is applied to a Standard Model 3 flavour oscillation model as a cross check under the scenarios with and without ν e appearance. The oscillation parameters measured by this model are ∆m 2 32 = (2.39 +0.23 −0.15 ) × 10 −3 eV 2 and θ 23 = 0.727 +0.22 −0.11 for the no ν e appearance result. An analysis of the resulting prediction reveals no evidence for active neutrino disappearance. The analysis is then performed using the 4 flavour neutrino oscillation model developed. Again this is done under the 2 scenarios of ν e appearance and no ν e appearance. The results of this analysis are ∆m 2 31 = (2.44 +0.23 −0.14 ) × 10 −3 eV 2 , θ 23 = 0.755 +0.19 −0.12 and θ 34 = 0.00 +0.35 for no ν e appearance and ∆m 2 31 = (2.46 +0.21 −0.14 ) × 10 −3 eV 2 , θ 23 = 0.849 +0.12 −0.19 and θ 34 = 0.00 +0.60 for ν e appearance. This is consistent with no oscillations between active and sterile neutrinos.