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We have measured the rates and spectra of neutral-current neutrino interactions in the MINOS detectors, which are separated by 734 km. A depletion in the rate at the far site would indicate mixing between [nu]{sub {mu}} and a sterile particle. The depletion of the total neutral-current event rate at the far site is limited to be below 17% at 90% confidence level without [nu]{sub e} appearance. Assuming oscillations occur at a single mass-squared splitting, a fit to the neutral- and charged-current energy spectra shows the fraction of [nu]{sub {mu}} oscillating to a sterile neutrino is 0.28{sub -0.28}{sup +0.25}(stat.+syst.). Including [nu]{sub e} appearance at the current experimental upper bound limits the depletion to be below 21% at 90% confidence level and the fit fraction of [nu]{sub {mu}} oscillating to a sterile neutrino is 0.43{sub -0.27}{sup +0.23}(stat.+syst.).
This thesis highlights data from MINOS, a long-baseline accelerator neutrino experiment, and details one of the most sensitive searches for the sterile neutrino ever made. Further, it presents a new analysis paradigm to enable this measurement and a comprehensive study of the myriad systematic uncertainties involved in a search for a few-percent effect, while also rigorously investigating the statistical interpretation of the findings in the context of a sterile neutrino model. Among the scientific community, this analysis was quickly recognized as a foundational measurement in light of which all previous evidence for the sterile neutrino must now be (re)interpreted. The existence of sterile neutrinos has long been one of the key questions in the field. Not only are they a central component in many theories of new physics, but a number of past experiments have yielded results consistent with their existence. Nonetheless, they remain controversial: the interpretation of the data showing evidence for these sterile neutrinos is hotly debated.
MINOS is a long-baseline neutrino oscillations experiment located at Fermi National Accelerator Laboratory (FNAL), USA. It makes use of the NuMI neutrino beamline and two functionally identical detectors located at distances of H"km and H"35km from the neutrino production target respectively. The Near Detector measures the composition and energy spectrum of the neutrino beam with high precision while the Far Detector looks for evidence of neutrino oscillations. This thesis presents work conducted in two distinct areas of the MINOS experiment: analysis of neutral current and charged current interactions. While charged current events are only sensitive to muon neutrino disappearance, neutral current events can be used to distinguish oscillations into sterile neutrinos from those involving only active neutrino species. A complete, preliminary neutral current study is performed on simulated data. This is followed by a more detailed investigation of neutral current neutrino interactions in the MINOS Near Detector. A procedure identifying neutral current interactions and rejecting backgrounds due to reconstruction failures is developed. Two distinct event classification methods are investigated. The selected neutral current events in the Near Detector are used to extract corrections to the neutral current cross-section in the MINOS Monte Carlo simulation as a function of energy. The resulting correction factors are consistent with unity. The main MINOS charged current neutrino disappearance analysis is described. We present the Monte Carlo tuning procedure, event selection, extrapolation from Near to Far Detector and fit for neutrino oscillations. Systematic errors on this measurement are evaluated and discussed in detail. The data are consistent with neutrino oscillations with the following parameters: 2.74 {sup +0.44}{sub -0.26} x 10−3 eV2 and sin2(2[theta]23)> 0.87 at 68% confidence level.
The centerpiece of the thesis is the search for muon neutrino to electron neutrino oscillations which would indicate a non-zero mixing angle between the first and third neutrino generations (θ13), currently the “holy grail” of neutrino physics. The optimal extraction of the electron neutrino oscillation signal is based on the novel “library event matching” (LEM) method which Ochoa developed and implemented together with colleagues at Caltech and at Cambridge, which improves MINOS’ (Main Injector Neutrino Oscillator Search) reach for establishing an oscillation signal over any other method. LEM will now be the basis for MINOS’ final results, and will likely keep MINOS at the forefront of this field until it completes its data taking in 2011. Ochoa and his colleagues also developed the successful plan to run MINOS with a beam tuned for antineutrinos, to make a sensitive test of CPT symmetry by comparing the inter-generational mass splitting for neutrinos and antineutrinos. Ochoa’s in-depth, creative approach to the solution of a variety of complex experimental problems is an outstanding example for graduate students and longtime practitioners of experimental physics alike. Some of the most exciting results in this field to emerge in the near future may find their foundations in this thesis.
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 v[mu] 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 provides 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 utilizing 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 ve appearance. The oscillation parameters measured by this model are [Delta]m322 = (2.39-0.15+0.23) x 10-3 eV2 and [theta]23 = 0.727-0.11+0.22 for the no ve 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 ve appearance and no ve appearance. The results of this analysis are [Delta]m312 = 2.44-0.14+0.23 x 10-3 eV2, [theta]23 = 0.755-0.12+0.19 and [theta]34 = 0.00+0.35 for no ve appearance and [Delta]m312 = (2.46-0.14+0.21) x 10-3 eV2, [theta]23 = 0.849-0.19+0.12 and [theta]34 = 0.00+0.60 for ve appearance. This is consistent with no oscillations between active and sterile neutrinos.
MINOS, Main Injector Neutrino Oscillation Search, is a long-baseline neutrino oscillation experiment in the NuMI muon neutrino beam at the Fermi National Accelerator Laboratory in Batavia, IL. It consists of two detectors, a near detector positioned 1km from the source of the beam and a far detector 734km away in Minnesota. MINOS is primarily designed to observe muon neutrino disappearance resulting from three avor oscillations. The Standard Model of Particle Physics predicts that neutrinos oscillate between three active avors as they propagate through space. This means that a muon type neutrino has a certain probability to later interact as a di erent type of neutrino. In the standard picture, the neutrino oscillation probabilities depend only on three neutrino avors and two mass splittings, [Delta]m2. An anomaly was observed by the LSND and MiniBooNE experiments that suggests the existence of a fourth, sterile neutrino avor that does not interact through any of the known Standard Model interactions. Oscillations into a theoretical sterile avor may be observed by a de cit in neutral current interactions in the MINOS detectors. A distortion in the charged current energy spectrum might also be visible if oscillations into the sterile avor are driven by a large mass-squared di erence, m2s 1 eV2. The results of the 2013 sterile neutrino search are presented here.
The Main Injector Neutrino Oscillation Search (MINOS) long-baseline experiment has been actively collecting beam data since 2005, having already accumulated 3 x 102° protons-on-target (POT). The several million neutrinos per year observed at the Near detector may improve the existing body of knowledge of neutrino cross-sections and the Near-Far comparison of the observed energy spectrum neutral current events constrains oscillations into sterile neutrinos. MINOS capabilities of observing neutral current neutrino events are described and the employed methodology for event selection is discussed, along with preliminary results obtained. An outlook on the expected neutral current related contributions from MINOS is also presented.
The MINOS experiment is a long-baseline neutrino oscillation experiment in the the NuMI beamline at Fermilab, USA. Using a near detector at 1 km distance from the neutrino production target, and a far detector at 735 km from the target, it is designed primarily to measure the disappearance of muon neutrinos. This thesis presents an analysis using MINOS data of the possibility of oscil- lation of the neutrinos in the NuMI beam to a hypothetical sterile flavour, which would have no Standard Model couplings. Such oscillations would result in a deficit in the neutral current interaction rate in the MINOS far detector relative to the expectation derived from the near detector data. The method used to identify neutral current and charged current events in the MINOS detectors is described and a new method of predicting and fitting the far detector spectrum presented, along with the effects of systematic uncertainties on the sterile neutrino oscillation analysis. Using this analysis, the fraction f{sub s} of the disappearing neutrinos that go to steriles is constrained to be below 0.15 at the 90% confidence level in the absence of electron neutrino appearance in the NuMI beam. With electron appearance at the CHOOZ limit, f{sub s}
This thesis will present a search for sterile neutrinos using data taken with the MINOS experiment between 2005 and 2012. MINOS is a two-detector on-axis experiment based at Fermilab. The NuMI neutrino beam encounters the MINOS Near Detector 1km downstream of the neutrino-production target before traveling a further 734km through the Earth's crust, to reach the Far Detector located at the Soudan Underground Laboratory in Northern Minnesota. By searching for oscillations driven by a large mass splitting, MINOS is sensitive to the existence of sterile neutrinos through looking for any energy-dependent perturbations using a charged-current sample, as well as looking at any relative deficit in neutral current events between the Far and Near Detectors. This thesis will discuss the novel analysis that enabled a search for sterile neutrinos covering five orders of magnitude in the mass splitting and setting a limit in previously unexplored regions of the parameter space $\left\{\Delta m^{2}_{41}, \sin^2\theta_{24}\right\}$, where a 3+1-flavour phenomenological model was used to extract parameter limits. The results presented in this thesis are sensitive to the sterile neutrino parameter space suggested by the LSND and MiniBooNE experiments.