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Measurement of the Panofsky Ratio Spuller, Joseph Edward


The π⁻p → π°n and π⁻p → γn have been investigated for stopped pions in a liquid hydrogen target. In order to separate the inflight π° → γγ decay (55 to 83 MeV photons) from the radiative capture photons (129)MeV), a large Nal(Tl) crystal of dimensions 46 cm Ø x 51 cm was used as a total energy detector. The energy resolution was 6% fwhm at 129 MeV, and this resulted in good separation between the π ° photons and the radiative capture photons. We show that the value of the Panofsky ratio is P = 1.546 ± 0.009, where the uncertainty is 50% statistical and 50% systematic in origin. (2.1 x 10⁵ stopped pions were observed.) Data on the timing response and data for the tail region of the energy response of the NaI detector are also presented. The latter was acquired through an n-γ coincidence. The timing response is shown to be a surprisingly good 2 ns and this was achieved by using constant fraction discriminators. A discussion of low-energy pion relations is included, and by using these relationships, it is shown that there is an inconsistency in the determination of the s-wave component of pion production in the π⁺d → pp reaction near threshold. The discrepancy is resolved, and in order to do this, it was found necessary to allow an energy dependence to the s-wave pion production amplitude. The low-energy pion relations are also used to relate the Panofsky ratio to the s-wave |a₁-a₃| scattering length. It is found that |a₁-a₃| = 0.261 ± 0.005 [Mathematical Formula].

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