Comparison ofπ+andπ−Lifetimes

A check on $\mathrm{CPT}$ invariance has been made by comparing the lifetimes of the charged pion and its antipion. The fraction of surviving pions in beams of ${\pi }^{+}$ and ${\pi }^{-}$ which were nearly identical in their spatial and momentum distributions were measured at ten positions along the beam using a liquid-hydrogen differential Čerenkov counter. Over 100 successive ${\pi }^{+}-{\pi }^{-}-{\pi }^{+}$ comparisons were made. Because of the method used, many possible systematic errors which affect an absolute lifetime measurement cancel out in determining the ratio of the lifetimes. The ratio measurement gave $\left(\frac{{\tau }_{+}}{{\tau }_{-}}\right)-1=0.0056\mathrm{}\pm 0.0028$ and the absolute ${\pi }^{+}$ lifetime was found to be 26.6±0.2 nsec.