= Solution
\b[Covered by the official notes:] comparison with a 200 keV neutrino mass (PDF p. 12; handwritten p. 7).<Symmetry and Relativity 2011 Exam Solution Notes>[PDF p. 12; handwritten p. 7: comparison with a 200 keV neutrino mass]{ref}
The notes stop at “no change”; the experimental implication is that this is a poorly conditioned <neutrino mass> measurement. In <relativistic two-body decay>, the corrections to the rest-frame energy and momentum enter through the square of the daughter <rest mass>, while the <Lorentz transformation> boosts both the massless value and its small correction. A measured laboratory energy or angle must therefore resolve a very small change against beam-energy spread, decay-angle uncertainty and detector resolution. \b[No visible change at the quoted precision does not establish zero neutrino mass.]
Back to article page
