University of Leicester
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A new determination of the charged pion mass an dmuon neutrino mass upper limit from exotic atom x-ray spectroscopy

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posted on 2014-12-15, 10:41 authored by Nicholas Nelms
This thesis describes an experiment that has made a new determination of the charged pion mass and from which a new upper limit of the muon neutrino mass has been calculated. The experimental approach uses a high-intensity negative pion beam injected into a cyclotron trap and stopped inside a nitrogen/oxygen mix gas-filled target cell where highly excited pionic and muonic atoms are formed. The energy of photons emitted during de-excitation is directly proportional to the reduced mass of the system, from which the mass of the orbiting particle can be determined. X-ray spectra from pionic nitrogen and muonic oxygen are measured using a high-resolution Bragg crystal spectrometer arranged in Johann geometry. A new large area detector comprising six, high quantum efficiency charge coupled devices is positioned at the focus to measure the reflections from the spectrometer. By using muonic oxygen X-rays as calibration for the pionic nitrogen line the negative pion mass has been determined as 139.57176 0.000259 MeV/c2, a precision of 1.85 ppm. Although more precise, this value is approximately 11 ppm higher than the current world average. Consequently, the muon neutrino mass upper limit has been calculated as 0.33 MeV/c2 (90% confidence level) which offers no new information over the current value of 0.17 MeV/c2. Investigations are underway to determine the validity of the 11 ppm discrepancy.


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Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD



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