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MINOS is a long baseline neutrino oscillation experiment. A manmade beam of predominantly muon neutrinos is detected both 1 km and 735 km from the production point by two functionally identical detectors. A comparison of the energy spectra measured by the two detectors shows the energy-dependent disappearance of muon neutrinos characteristic of oscillations and allows a measurement of the parameters governing the oscillations. This thesis presents work leading to measurements of disappearance in the 6% {bar {nu}}{sub {mu}} background in that beam. A calibration is developed to correct for time-dependent changes in the responses of both detectors, reducing the corresponding uncertainty on hadronic energy measurements from 1.8% to 0.4% in the near detector and from 0.8% to 0.4% in the far detector. A method of selecting charged current {bar {nu}}{sub {mu}} events is developed, with purities (efficiencies) of 96.5% (74.4%) at the near detector, and 98.8% (70.9%) at the far detector in the region below 10 GeV reconstructed antineutrino energy. A method of using the measured near detector neutrino energy spectrum to predict that expected at the far detector is discussed, and developed for use in the {bar {nu}}{sub {mu}} analysis. Sources of systematic uncertainty contributing to the oscillation measurements are discussed. In the far detector, 32 charged current {bar {nu}}{sub {mu}} events are observed below a reconstructed energy of 30 GeV, compared to an expectation of 47.8 for [Delta]{bar m}{sub atm}2 = [Delta]m{sub atm}2, sin2(2{bar [theta]}23) = sin2(2{theta}23). This deficit, in such a low-statistics sample, makes the result difficult to interpret in the context of an oscillation parameter measurement. Possible sources for the discrepancy are discussed, concluding that considerably more data are required for a definitive solution. Running MINOS with a dedicated {bar {nu}}{sub {mu}} beam would be the ideal continuation of this work.
Experimental evidence has established that neutrino flavor states evolve over time. A neutrino of a particular flavor that travels some distance can be detected in a different neutrino flavor state. The Main Injector Neutrino Oscillation Search (MINOS) is a long-baseline experiment that is designed to study this phenomenon, called neutrino oscillations. MINOS is based at Fermilab near Chicago, IL, and consists of two detectors: the Near Detector located at Fermilab, and the Far Detector, which is located in an old iron mine in Soudan, MN. Both detectors are exposed to a beam of muon neutrinos from the NuMI beamline, and MINOS measures the fraction of muon neutrinos that disappear after traveling the 734 km between the two detectors. One can measure the atmospheric neutrino mass splitting and mixing angle by observing the energy-dependence of this muon neutrino disappearance. MINOS has made several prior measurements of these parameters. Here I describe recently-developed techniques used to enhance our sensitivity to the oscillation parameters, and I present the results obtained when they are applied to a dataset that is twice as large as has been previously analyzed. We measure the mass splitting ?m232 = (2.32-0.08+0.12) x 10-3 eV2/c4 and the mixing angle sin2(2?32) > 0.90 at 90% C.L. These results comprise the world's best measurement of the atmospheric neutrino mass splitting. Alternative disappearance models are also tested. The neutrino decay hypothesis is disfavored at 7.2? and the neutrino quantum decoherence hypothesis is disfavored at 9.0?.
The Main Injector Neutrino Oscillation Search (MINOS) is a long baseline experiment that was built for studying the neutrino oscillation phenomena. The MINOS experiment uses high intensity muon neutrino and antineutrino beams created by Neutrinos at the Main Injector facility (NuMI) at the Fermi National Accelerator Laboratory (Fermilab). Neutrino interactions are recorded by two sampling steel-scintillator tracking calorimeters: 0.98 kton Near Detector at Fermilab, IL and 5.4 kton Far Detector at the Soudan Underground Laboratory, MN. These two detectors are functionally identical, which helps to reduce the systematic uncertainties in the muon neutrino and antineutrino disappearance measurements. The Near Detector, located 1.04 km from the neutrino production target, is used to measure the initial beam composition and neutrino energy proximal to the neutrino source. The collected data at the Near Detector is then used to predict energy spectrum in the Far Detector. By comparing this prediction to collected data at the Far Detector, which is 735 km away from the target, it enables a measurement of a set of parameters that govern the neutrino oscillation phenomenon. The flexibility of the NuMI beam configuration and the magnetization of the MINOS detectors facilitate the identification of v[subscript mu] and v̄[subscript mu] charged-current interactions on an event-by-event basis. This enables one to measure neutrino and antineutrino oscillation parameters independently and therefore allows us to test the CPT symmetry in the lepton sector. To enhance the sensitivity of the oscillation parameters measurement, a number of techniques have been implemented. Event classification, shower energy estimation and energy resolution bin fitting, which are described in this dissertation, are three of these techniques. Moreover, the most stringent constraints on oscillation parameters can be achieved by combining multiple data sets. This dissertation reports the measurement of antineutrino oscillation parameters using the complete MINOS accelerator and atmospheric data set of charged-current v̄[subscript mu] events.
The MINOS experiment utilizes the NuMI neutrino beam to study the phenomenon of neutrino oscillations. Muon neutrinos are sent over a baseline of 735 km, with a detector near the production point at Fermilab and one at the Soudan underground laboratory in northern Minnesota. By observing the?{sub {mu}} disappearance characteristic of oscillations, MINOS can measure the oscillation parameters. MINOS has previously made the best measurement of the atmospheric-regime mass splitting to date. New results are presented in which the data-set is doubled. Further analysis improvements, and the inclusion of additional event samples, further improve the sensitivity to the oscillation parameters. The mixing angle?13 is currently not measured to differ from zero. By searching for?{sub e} appearance in the?{sub {mu}} beam, MINOS is able to set new limits on the value of?13. An observation of the neutral current interaction rate at the far detector allows limits to be placed on the existence of sterile neutrinos. From September 2009 to March 2010, MINOS has taken data with a dedicated {bar {nu}}{sub {mu}} beam, allowing the first direct precision measurement of the antineutrino oscillation parameters in the atmospheric regime.
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.
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.
The Main Injector Neutrino Oscillation Search (MINOS) is a long baseline experiment that was built for studying the neutrino oscillation phenomena. The MINOS experiment uses high intensity muon neutrino and antineutrino beams created by Neutrinos at the Main Injector facility (NuMI) at the Fermi National Accelerator Laboratory (Fermilab). Neutrino interactions are recorded by two sampling steel-scintillator tracking calorimeters: 0.98\, kton Near Detector at Fermilab, IL and 5.4\, kton Far Detector at the Soudan Underground Laboratory, MN. These two detectors are functionally identical, which helps to reduce the systematic uncertainties in the muon neutrino and antineutrino disappearance measurements. The Near Detector, located 1.04\, km from the neutrino production target, is used to measure the initial beam composition and neutrino energy proximal to the neutrino source. The collected data at the Near Detector is then used to predict energy spectrum in the Far Detector. By comparing this prediction to collected data at the Far Detector, which is 735\, km away from the target, it enables a measurement of a set of parameters that govern the neutrino oscillation phenomenon. \\ \indent The flexibility of the NuMI beam configuration and the magnetization of the MINOS detectors facilitate the identification of $\nu_{\mu}$ and $\bar{\nu}_{\mu}$ charged-current interactions on an event-by-event basis. This enables one to measure neutrino and antineutrino oscillation parameters independently and therefore allows us to test the CPT symmetry in the lepton sector. To enhance the sensitivity of the oscillation parameters measurement, a number of techniques have been implemented. Event classification, shower energy estimation and energy resolution bin fitting, which are described in this dissertation, are three of these techniques. Moreover, the most stringent constraints on oscillation parameters can be achieved by combining multiple data sets. \\ \indent This dissertation reports the measurement of antineutrino oscill! ation parameters using the complete MINOS accelerator and atmospheric data set of charged-current $\bar{\nu}_{\mu}$ events. This set comprises exposures of (i) 3.36\times 10^{20} proton-on-target (POT) in the \bar{\nu}_{\mu}-beam mode, (ii) 10.71\times 10^{20} POT in the \nu_{\mu}-beam mode, and (iii) 37.88 kton yr of atmospheric antineutrinos. The data analysis provides the world's most precise measurement to date on the antineutrino oscillation parameters: $
One of the primary goals in neutrino physics at the present moment is to make a measurement of the neutrino oscillation parameter $\theta_$. This parameter, in addition to being unknown, could potentially allow for the introduction of CP violation into the lepton sector. The MINOS long-baseline neutrino oscillation experiment has the ability to make a measurement of this parameter, by looking for the oscillation of muon neutrinos to electron neutrinos between a Near and Far Detector over a distance of 735 km. This thesis discusses the development of an analysis framework to search for this oscillation mode. Two major improvements to pre-existing analysis techniques have been implemented by the author. First, a novel particle ID technique based on strip topology, known as the Library Event Matching (LEM) method, is optimized for use in MINOS. Second, a multiple bin likelihood method is developed to fit the data. These two improvements, when combined, increase MINOS' sensitivity to $\sin^2(2\theta_)$ by 27\% over previous analyses. This thesis sees a small excess over background in the Far Detector. A Frequentist interpretation of the data rules out $\theta_=0$ at 91\%. A Bayesian interpretation of the data is also presented, placing the most stringent upper boundary on the oscillation parameter to date, at $\sin^2(2\theta_)