Browsing by Author "Busenitz, Jerome K."
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Item Antineutrino neutral current interactions in MiniBooNE(University of Alabama Libraries, 2012) Dharmapalan, Ranjan; Stancu, Ion; University of Alabama TuscaloosaThe antineutrino nucleon neutral current elastic scattering cross section measured at the MiniBooNE experiment is reported. The data set corresponds to 10.1 × 10^20 protons on target which is a world record neutral current elastic antineutrino sample. An antineutrino to neutrino neutral current scattering cross section ratio is measured after accounting for all associated errors. This is the first time such a ratio has been experimentally reported. Previous MiniBooNE neutrino cross section measurements have indicated a higher value for the axial mass, M_A, as compared to the nominal value of M_A=1.0 GeV. A Χ^2 test was performed to find the best value of M_A which matches the antineutrino neutral current elastic data. Finally, an exciting possibility to search for dark matter in the MiniBooNE experiment, using the neutral current interactions is discussedItem Laser calibration and event reconstruction in Double Chooz experiment(University of Alabama Libraries, 2013) Sun, Yujing; Stancu, Ion; University of Alabama TuscaloosaThe neutrino oscillation mixing angle θ13<\sub> was the last mixing angle that had not been determined precisely in 2006 when I started my Ph.D studies. It is exciting to witness how θ13<\sub> has evolved from a limit to a precisely measured mixing angle in a short period. The Double Chooz reactor neutrino experiment was the first to report strong evidence for a non-vanishing value of θ13<\sub> at the beginning of 2012. The latest analysis, which includes a combined “rate+shape” analysis of hydrogen and gadolinium capture inverse β–decay events, has yielded sin<\super>2<\super> 2θ13<\sub> = 0.109 ± 0.035 with only one detector running. This value is consistent with the current numbers from the Daya Bay and Reno experiments. In such a high-precision experiment, precise calibrations are crucial in reaching the ultimate sensitivity. The laser calibration system was developed by the University of Alabama group to calibrate PMT constants such as gains and time offsets, as well as measure the charge likelihoods which are used in the event energy reconstruction and supplement the time likelihoods in improving the position reconstruction accuracy. The second part of this thesis is devoted to the hardware and software development of the laser calibration system, as well as MC studies and data analyses for extracting the PMT gains, time offsets and charge likelihoods. The event reconstruction utilizes the PMT time and charge information to determine the event location and energy, which are essential parameters for all physics analyses. A good understanding of the detector response significantly reduces the detector related systematic errors and improves the sensitivity, especially in the two detector phase, where the dominant uncertainties from the reactor flux mostly cancel out. The third part of this thesis is dedicated to the reconstruction algorithm developed by our group, position accuracy studies and energy reconstruction studies, which aims towards fully understanding the detector response.Item Magnetic anisotropy graded media and Fe-Pt alloy thin films(University of Alabama Libraries, 2009) Lu, Zhihong; Butler, W. H.; University of Alabama TuscaloosaAnisotropy graded media is promising to overcome the writability problem in achieving ultrahigh areal density for magnetic recording media. To more conveniently study and compare various media with regard to a particular figure of merit, a new energy landscape method of analysis is suggested. Using this method, the theoretical limit of the figure of merit for a graded medium is found to be 4. This limit can be approached by a graded medium with anisotropy quadratically increasing from zero to its maximum value. In order to characterize the anisotropy distribution of a graded medium, hard axis loops of graded media with various anisotropy profiles are simulated and analyzed. It is found that the second derivative of the hard axis loop can give useful information on the anisotropy distribution in a graded medium. Fe₅₀Pt₅₀ with the L1₀ structure, as one of the magnetically hardest materials, has great potential for media application. By using a first-principles calculation method, the magnetic and electronic structures of L1₀ structured Fe₅₀Pt₅₀ have been studied. These calculations show that although the ferromagnetic phase is the most stable phase for Fe₅₀Pt₅₀ with the L1₀ structure, there is a competition between the antiferromagnetic and the ferromagnetic phases when the ratio of lattice constants, c/a, decreases. Experimental investigations of Fe₅₀Pt₅₀ films with graded order parameter fabricated by varying the growth temperature during deposition demonstrate that these films have much smaller switching field than fully ordered Fe₅₀Pt₅₀, which suggests it is possible to make graded media by using this kind of films. Fe₁₀₋ₓPtₓ films with compositional gradient were also studied; however, the large easy axis dispersion in these films makes them unsuitable for the fabrication of graded media. Films with [FePt₃ordered)/FePt₃ (disordered)]n superlattices were deposited on MgO substrates and sapphire substrates. It was found that the exchange bias in superlattices deposited on MgO substrate show higher exchange bias field. Polarized neutron reflectivity results show that ferromagnetic layers on MgO substrates contain more antiferromagnetic component than those on sapphire substrates. The larger exchange bias of the superlattice on MgO substrate is hypothesized to be due to larger exchange bias in its ferromagnetic layers.Item Measuring the neutrino mixing angle theta-13 with the double chooz far detector(University of Alabama Libraries, 2012) Ostrovskiy, Igor; Busenitz, Jerome K.; University of Alabama TuscaloosaThe neutrino mixing angle theta-13 is the last one which value is still unknown. This dissertation presents an analysis suggesting a non-zero value of the theta-13. The analysis is based on four months of data taken with the far Double Chooz reactor anti-neutrino detector. Using only rate information yields a best fit value of sin2(2theta-13) equal to 0.0934±0.0785 (1 sigma). Incorporating information on the shape of the signal energy spectrum in the analysis results in a best fit value of 0.0849±0.0509 (1 sigma). Based on frequentist studies, sin2(2theta-13)=0 is excluded at the 92.6% confidence level. The frequentist construction using delta chi-square as an ordering rule gives [0.0098, 0.1825] interval for sin2(2theta-13) at 90% C.L.Item A Monte Carlo approach to 7Be solar neutrino analysis with KamLAND(University of Alabama Libraries, 2012) Grant, Christopher; Piepke, Andreas; University of Alabama TuscaloosaTerrestrial measurements of neutrinos produced by the Sun have been of great interest for over half a century because of their ability to test the accuracy of solar models. The first solar neutrinos detected with KamLAND provided a measurement of the ^8B solar neutrino interaction rate above an analysis threshold of 5.5 MeV. This work describes efforts to extend KamLAND's detection sensitivity to solar neutrinos below 1 MeV, more specifically, those produced with an energy of 0.862 MeV from the ^7Be electron-capture decay. Many of the difficulties in measuring solar neutrinos below 1 MeV arise from backgrounds caused abundantly by both naturally occuring, and man-made, radioactive nuclides. The primary nuclides of concern were ^210Bi, ^85Kr, and ^39Ar. Since May of 2007, the KamLAND experiment has undergone two separate purification campaigns. During both campaigns a total of 5.4 ktons (about 6440 m^3) of scintillator was circulated through a purification system, which utilized fractional distillation and nitrogen purging. After the purification campaign, reduction factors of 1.5 x 10^3 for ^210Bi and 6.5 x 10^4 for ^85Kr were observed. The reduction of the backgrounds provided a unique opportunity to observe the ^7Be solar neutrino rate in KamLAND. An observation required detailed knowledge of the detector response at low energies, and to accomplish this, a full detector Monte Carlo simulation, called KLG4sim, was utilized. The optical model of the simulation was tuned to match the detector response observed in data after purification, and the software was optimized for the simulation of internal backgrounds used in the ^7Be solar neutrino analysis. The results of this tuning and estimates from simulations of the internal backgrounds and external backgrounds caused by radioactivity on the detector components are presented. The first KamLAND analysis based on Monte Carlo simulations in the energy region below 2 MeV is shown here. The comparison of the Δχ^2 between the null hypothesis and the existence of the ^7Be solar neutrino signal in the data shows a change of 27.9 units, providing evidence that the signal is statistically favored. This analysis reports a measured interaction rate from ^7Be solar neutrinos of R = 343.3 ± 65.0(stat) ± 99.2(syst) events/(kton·day), which corresponds to a total flux of ɸ = (3.41 ±; 1.18) x 10^9 cm^-2 s^-1. The ^7Be solar neutrino flux reported in this work is only the second measurement made of this quantity worldwide. It provides an important cross-check of the Borexino experiment. The flux measurement reported here agrees within 1σ with the standard solar model predictions thus validating our basic understanding of solar fusion reaction processes.Item Neutrino-nucleus neutral current elastic interactions measurement in MiniBooNE(University of Alabama Libraries, 2010) Perevalov, Denis; Stancu, Ion; University of Alabama TuscaloosaThe MiniBooNE experiment at the Fermi National Accelerator Laboratory (Fermilab) was designed to search for electron to muon neutrino oscillations at Delta m^2~1 eV^2 using an intense neutrino flux with an average energy of about 700 MeV. From 2002 to 2009 MiniBooNE has accumulated more than 1.0x10^{21} protons on target (POT) in both neutrino and antineutrino modes. MiniBooNE provides a perfect platform for detailed measurements of exclusive and semiinclusive neutrino cross-sections, for which MiniBooNE has the largest samples of events up to date, such as neutral current elastic (NCE), neutral current pi^0, charged current quasi-elastic (CCQE), charged current pi^+, and other channels. These measured cross-sections, in turn, allow to improve the knowledge of nucleon structure. This thesis is devoted to the study of NCE interactions. Neutrino-nucleus neutral current elastic scattering accounts for about 18% of all neutrino interactions in MiniBooNE. Using a high-statistics, high purity sample of NCE interactions in MiniBooNE, the flux-averaged NCE differential cross-section has been measured and is being reported here. Further study of the NCE cross-section allowed for probing the structure of nuclei. The main interest in the NCE cross-section is that it may be sensitive to the strange quark contribution to the nucleon spin, $Delta s$, this however requires a separation of NCE proton from NCE neutron events, which in general is a challenging task. MiniBooNE uses a Cherenkov detector, which imposes restrictions on the measured nucleon kinematic variables, mainly due to the impossibility to reconstruct the nucleon direction below the Cherenkov threshold. However, at kinetic energies above this threshold MiniBooNE is able to identify NCE proton events that do not experience final state interactions. These events were used for the $Delta s$ measurement. In this thesis MiniBooNE reports the NCE (n+p) cross-section, the measurement of the axial mass, $M_A$, and the $Delta s$ parameter from the NCE data.Item A wire source deployment system for calibration of the double chooz near detector(University of Alabama Libraries, 2016) Fernandes, Shak; Busenitz, Jerome K.; University of Alabama TuscaloosaThe reactor neutrino experiment, Double Chooz (DC), observes the electron antineutrino flux from two nuclear reactors located in Chooz, France. Its primary purpose is to measure the neutrino oscillation parameter sin2 2θ13 via inverse beta decay within two functionally identical detectors which utilise a gadolinium doped liquid scintillator active target region. This thesis presents a complete description of the design, construction and installation of the DC near detector radioactive source deployment guide tube (GT) system. During the installation process a photographic and theodolite survey were conducted to determine the precise location of the GT within the detector. Data from both surveys were analysed and compared to obtain a set of coordinates useful for calibration purposes. Post installation, a system verification test was performed to determine the function of the GT. After the first year of successful physics data acquisition using the near detector a calibration campaign was conducted. It was the first time both detectors were calibrated using the GT system. One of several main calibration systems, the GT provides the required accuracy to aid oscillation analyses through the precise knowledge of the energy response and neutron detection efficiency within both detectors. This aids in the minimisation of systematic uncertainties between both detectors.