introduction-weak-interaction-volume-one

where
C . = C! = G . /f 2 (3 .7 .7f )
We find that a is the angular correlation factor in polarized neutro n
decay, A and B respectively the electron and antineutrino asymmetr y
parameters, and D the electron-antineutrino correlation coefficient .
Presence of the latter term would indicate both T and C noninvariance .
Experimentally (54), a beam of about 1 0 8 876-polarized thermal neutrons
was obtained by reflecting a collimated neutron beam at a glancing angl e
(8') from a cobalt mirror magnetized at a normal to the beam's directio n
of propagation . The neutrons were then admitted into a vacuum chamber i n
which a number of them decayed . Disintegration electrons were recorded
by a scintillation counter on the right hand side of the chamber, i n
time coincidence with the recoil protons which were detected by an electro n
multiplier . A grid was placed at the opposite side of the beam from th e
proton detector, and a potential difference of 12 000 V was applied betwee n
the grid and the first dynode of the electron multiplier . Since it was
important to have as high an intensity as possible, the recording unit s
were made as large as possible : the scintillation counter head had
diameter of 15 cm and the first dynode of the electron multiplier had a n
area of about 225 cm 2 . Measurements of the anisotropy of electrons in
neutron decay were made by polarizing the beam towards and away from th e
electron detector . These demonstrated that about 20% more electron s
were emitted opposite to the spin direction than along it . Comparing thi s
with the theoretical distributio n
I(e) = 1 + A (v/c) cos , (3.7 .8 )
we obtain
A = - 0 .114 ± 0 .019 . (3 .7 .9)
The angular distribution of decay antineutrinos was deduced by observin g
both electron and proton anisotropy, yieldin g
B = 0 .88 -* 0 .15 . (3 .7 .10 )
The parameter D was calculated by measuring simultaneously the direction s
in which the electron and antineutrino were emitted with respect to th e
neutron spin . No indication of time-reversal noninvariance was revealed ,
a