The pion beta decay (
) is a semi-leptonic
process involving only vector interactions. It is a transition between spin zero
members of an isomultiplet and is therefore similar to superallowed Fermi transitions
in nuclear beta decay. The measurements of the 
values of the Fermi decays
can be used to test the CVC hypothesis, quark-lepton universality and the unitarity
of the CKM quark mixing matrix. From the neutron beta decay which involves the full
V-A structure of the weak interactions, it is possible to extract the mixing angle
between the up and the down quarks by measuring the ratio of the weak vector to the
axial-vector coupling constants and the neutron lifetime. The discrepancy between
Fermi beta decay data and the neutron beta decay data dictates the need for a new
precision experiment. Pion beta decay (
)
being the most direct test of CVC, presents an
independent approach to extract the weak vector coupling constant without the
complication of nuclear corrections, screening effects and final states Coulomb
interactions. Only radiative corrections are needed in the calculation of the pion
beta decay rate, and these corrections have been evaluated up to the leading terms in
and amount to 
. Experimentally however, the study of the pion
beta decay is complicated by its small branching ratio. The most precise measurement of
the pion beta decay rate to date is in good agreement with theory but stands at 
experimental accuracy. It is desirable to improve upon this result since it is not
precise enough to test the full extent of radiative corrections. Therefore, an
experiment has been designed to do a precise measurement of the pion beta
decay rate at the Paul Scherrer Institute in Switzerland. During the first phase of
the experiment, an attempt will be made to measure the decay rate with an overall
uncertainty of 
. At this level of precision, it will be possible to test the
CVC hypothesis and the radiative corrections, and to compare the Fermi beta decay data
to the neutron decay data. An even more precise measurement will be made during the
second phase of the experiment, reducing the uncertainty to the level of
-
. This will allow a test of the CKM unitarity and place constraints on
possible new physics beyond the Standard Model of the elementary particle physics.