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Interpretation of the data on
and .
The fair agreement between measured and calculated half lives in
decay suggests that the same models can reasonably predict the matrix elements
for the other decay modes. Table
lists the measured
half life limits from several experiments. For ^{128}Te, it was
assumed that the geochemically determined half life is a lower limit for
that of
decay. The corresponding neutrino mass limits, using the QRPA calculation
of Caltech as well as from two other groups, are shown. The spread between
the limits for a given half life is largest for ^{76}Ge, and relatively
small for the other, heavier, nuclei. This spread can be considered a measure
of the uncertainty associated with the
matrix elements. The last column gives the limits obtained with the shell
model matrix elements of StrasbourgMadrid. One sees that the ^{76}Ge
data give the most constraining limit. In all, one may conclude that the
various experiments give:
Table: Measured lower limits for the halflife of various
transitions. Deduced upper limits on the effective coupling constant .

[yr]
(90 % CL) 
Caltech 
direct 

< (3.9  4.4) 
< (2.5  3.1) 
< (1.2 1.8) 

geochem. ^{128}Te 
> 2.5  7.7 
< (2  5) 

Table
shows some measured half life limits on
decay and the corresponding limits on
obtained from the more conservative Caltech matrix elements. Here the geochemical
^{128}Te data are the most constraining. Of the direct searches
the ^{136}Xe experiment gives the most stringent limit. In any
event, one may conclude that the effective coupling constant is bound by: .
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