Mean Lifetime of theπ0Meson

Abstract

An experiment is described to measure the mean life of the ${\ensuremath{\pi}}^{0}$ meson using nuclear emulsions. The basic method has also been employed by other workers in recent years, viz., the determination of the flight distances of ${\ensuremath{\pi}}^{0}$ mesons produced at a unique velocity in the ${K}_{\ensuremath{\pi}2}$ decay mode of the ${K}^{+}$ meson and decaying through the mode ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}{e}^{+}{e}^{\ensuremath{-}}$. The coordinates of the grains composing the tracks in 67 such events were measured and the flight distances of the ${\ensuremath{\pi}}^{0}'\mathrm{s}$ determined by geometrical reconstruction of the events. It was considered that an accurate estimation of the various errors involved was essential to the correct computation of the lifetime and such estimations were attempted. The effect of the presence of a certain type of spurious event upon the final results is demonstrated. The value for the mean lifetime obtained is ${\ensuremath{\tau}}_{{\ensuremath{\pi}}^{0}}=({1.6}_{\ensuremath{-}0.5}^{/+0.6})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ sec.