Determination ofπ-Meson Masses by Neutron Time of Flight

Abstract

Time-of-flight techniques were used to measure the velocities of the neutrons from the reactions, at rest, ${\pi }^{-}+p\to n+{\pi }^0$ and ${\pi }^{-}+p\to n+\gamma$. From these velocities the ${\pi }^{-}$ mass and the ${\pi }^{-}-{\pi }^0$ mass difference were obtained, with the results $m_{{\pi }^{-}}=139.69\mathrm{}\pm 0.41$ MeV/${\mathit{c}}^2$ and $m_{{\pi }^{-}}-m_{{\pi }^0}=4.6056\mathrm{}\pm 0.0055$ MeV/${\mathit{c}}^2$. The neutron velocity distribution about the mean velocity was measured and found to have an rms deviation of (8.0±1.5) × ${10}^6$ cm/sec.