limits for Up: Neutrino
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Mass limits for
These measurements apply to , the dominant mass eigenstate in .
The decay of pions is the
most appropriate process to search for this neutrino mass. In case of pion
decay at rest the square of the muon momentum is: .
A massive neutrino would reduce the muon momentum. In a recent paper the
up to now most precise measurement of from stopped pions has been reported.
The group at PSI (Switzerland) improved former limits by using a beam of
muons originating from the decay of -mesons stopped at the surface of a
pion production target. The muon momenta are analysed by a magnetic spectrometer,
the muons are detected by a silicon microstrip counter and a single silicon
surface barrier detector. The muon momentum was measured with great accuracy
to be MeV/c yielding
an upper limit for the neutrino mass of MeV
at 90% CL.