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Testing CPT conservation using the NuMI neutrino beam with the MINOS experiment

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posted on 2023-06-07, 15:32 authored by David John Auty
The MINOS experiment was designed to measure neutrino oscillation parameters with muon neutrinos. It achieves this by measuring the neutrino energy spectrum and flavour composition of the man-made NuMI neutrino beam 1km after the beam is formed and again after 735 km. By comparing the two spectra it is possible to measure the oscillation parameters. The NuMI beam is made up of 7.0% µ, which can be separated from the µ because the MINOS detectors are magnetised. This makes it possible to study µ oscillations separately from those of muon neutrinos, and thereby test CPT invariance in the neutrino sector by determining the µ oscillation parameters and comparing them with those for µ, although any unknown physics of the antineutrino would appear as a difference in oscillation parameters. Such a test has not been performed with beam µ before. It is also possible to produce an almost pure µ beam by reversing the current through the magnetic focusing horns of the NuMI beamline, thereby focusing negatively, instead of positively charged particles. This thesis describes the analysis of the 7% µ component of the forward horn current NuMI beam. The µ of a data sample of 3.2×1020 protons on target analysis found 42 events, compared to a CPT conserving prediction of 58.3+7.6 -7.6(stat.)+3.6 -3.6(syst.) events. This corresponds to a 1.9 deficit, and a best fit value of m2 32 = 18 × 10-3 eV2 and sin2 223 = 0.55. This thesis focuses particularly on the selection of µ events, and investigates possible improvements of the selection algorithm. From this a different selector was chosen, which corroborated the findings of the original selector. The thesis also investigates how the systematic errors affect the precision of m2 32 and sin2 223. Furthermore, it describes a study to determine the gains of the PMTs via the single-photoelectron spectrum. The results were used as a crosscheck of the gains determined at higher intensities by an LED-based light-injection system.


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  • eng


University of Sussex

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