Portal de Periódicos da CAPES

Determination of π -Meson Masses by Neutron Time of Flight

1963; American Institute of Physics; Volume: 130; Issue: 1 Linguagem: Inglês

10.1103/physrev.130.341

1536-6065

John B. Czirr,

Atomic and Molecular Physics

Time-of-flight techniques were used to measure the velocities of the neutrons from the reactions, at rest, ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+{\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+\ensuremath{\gamma}$. From these velocities the ${\ensuremath{\pi}}^{\ensuremath{-}}$ mass and the ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\pi}}^{0}$ mass difference were obtained, with the results ${m}_{{\ensuremath{\pi}}^{\ensuremath{-}}}=139.69\ifmmode\pm\else\textpm\fi{}0.41$ MeV/${\mathit{c}}^{2}$ and ${m}_{{\ensuremath{\pi}}^{\ensuremath{-}}}\ensuremath{-}{m}_{{\ensuremath{\pi}}^{0}}=4.6056\ifmmode\pm\else\textpm\fi{}0.0055$ MeV/${\mathit{c}}^{2}$. The neutron velocity distribution about the mean velocity was measured and found to have an rms deviation of (8.0\ifmmode\pm\else\textpm\fi{}1.5) \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ cm/sec.Negative $\ensuremath{\pi}$ measons from the 184-in. cyclotron were degraded by carbon and stopped in liquid hydrogen. The neutrons were detected in a plastic scintillator viewed by seven photomultiplier tubes. Time was measured for each event from the time of detection of a $\ensuremath{\gamma}$ ray associated with that event. The $\ensuremath{\gamma}$-detector signal was delayed and photographed along with the neutron signal on an oscilloscope trace. Neutron times of flight were measured over distances of 17, 47, and 67 ft.