Precision measurement of positron polarization inGa68decay based on the use of a new positron polarimeter

Abstract

We report a new measurement of positron polarization ($\overrightarrow{P}$) in ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$ decay. Using a new polarimeter the asymmetry ($A$) in the decay of positronium in a magnetic field was measured to 5%. When combined with a calculation of the positron depolarization on stopping in MgO powder the overall uncertainty in $P$ is 11%. The most precise prior determination of $P$ was to 12% accuracy. An eventual precision of 1% in $A$ and 0.1% in comparison of asymmetries from different sources is anticipated. In addition to the ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$ work we point out the possible use of the polarimeter in a number of new measurements including a determination of $e^{+}$ polarization in ${\mu }^{+}$ and nuclear decay and in a $g-2\mathrm{}$ experiment.