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The Production of Positive Pions by 341-Mev Protons on Protons

1953; American Institute of Physics; Volume: 91; Issue: 3 Linguagem: Inglês

10.1103/physrev.91.677

1536-6065

W. F. Cartwright, C. Richman, Marian Whitehead, Howard A. Wilcox,

Nuclear Physics and Applications

The production of positive pions by protons on protons has been studied at 0\ifmmode^\circ\else\textdegree\fi{}, 35\ifmmode^\circ\else\textdegree\fi{}, and 58\ifmmode^\circ\else\textdegree\fi{} to the beam of 341-Mev protons produced by the Berkeley synchrocyclotron. In the collision of two protons, two reactions are possible which lead to a ${\ensuremath{\pi}}^{+}$ meson: (1) $P+P\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+D$ and (2) $P+P\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+N+P$. The experimental results at 0\ifmmode^\circ\else\textdegree\fi{} show an energy spectrum from 0 to 70 Mev which is fairly flat except for a large peak at the high-energy end. The flat portion of the spectrum can only be due to reaction (2). A comparison of the shape of the peak with the results of the phenomenological theory of Brueckner and Watson shows that the peak is due solely to reaction (1).This fact, together with a measurement of the energy of the beam and of the energy of the pions from reaction (1), gives the value 275.1\ifmmode\pm\else\textpm\fi{}2.5 electron masses for the mass of the positive pion. The angular distribution in the center-of-mass system for reaction (1) as obtained from the data at the above three angles, is $(3.3\ifmmode\pm\else\textpm\fi{}1.2)[0.11\ifmmode\pm\else\textpm\fi{}0.06+{cos}^{2}\ensuremath{\theta}]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}29}$ ${\mathrm{cm}}^{2}$ ${\mathrm{sterad}}^{\ensuremath{-}1}$, and the total cross section for reaction (1) is (1.8\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}28}$ ${\mathrm{cm}}^{2}$.These results have been compared with the results obtained by Durbin, Loar, and Steinberger and by Clark, Roberts, and Wilson on the inverse reaction, ${\ensuremath{\pi}}^{+}+D\ensuremath{\rightarrow}P+P$. Using the theorem of detailed balancing, these experiments lead to the value zero for the spin of the positive pion with good certainty.