The goal of the experiment is a 1% measurement of 
(
). The capture rate will be measured as 
,
thus
. As
a result the lifetime of the positive and negative muon have to be measured
with at least 10 ppm precision, if both have to be determined. At present, even
the positive muon lifetime is only known to 20 ppm, though recent experiments
propose to reduce this error to 1 ppm [17,18]. Then, in principle,
only a 14 ppm measurement of the negative muon lifetime in hydrogen is required
for the present experiment. Nevertheless, as regards systematics, it is much
preferable to measure both 
and 
simultaneously
in a single experiment.