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Pion induced pion production on Oxygen at 280 MeV Rozon, Francis Martin


A first coincident measurement of the pion induced pion production reaction cross-section on a complex nucleus (A > 2) has been successfully performed. In particular, the reaction ¹⁶O(π⁺,π⁺,π⁻) was measured at 280 MeV incident pion energy. The only previous published measures of this reaction on nuclei consisted of a dated measurement done on emulsion nuclei [BBD*69] and did not provide very stringent limits to the nuclear cross section. Single arm experiments have previously been done elsewhere on the proton [BJK*80] and the deuteron [PGM*84]. The reaction was measured at TRIUMF using the QQD magnetic spectrometer in coincidence with the CARUZ [RGR88], a total absorption scintillator range telescope. The measured four-fold differential cross sections were extrapolated to the unmeasured portions of the phase-space to extract the total reaction cross-section at 280 MeV, which was found to be σtot = 2.250 ± .350m6. The (π,2π) cross-section is thus observed to provide approximately 40% of the inclusive double charge exchange cross section [Woo84] at this energy. The model of [OV86] is found to explain many of the features of the data, including σtot. The present data do not preclude effects due to pion condensate precursor phenomena as proposed by [CE83] but they do not support the existence of a strong effect. The data are also compared to kinematical Monte Carlo simulations of some possible reaction mechanisms and it is found that the presence of an intermediate ∆ can aid the explanation of the low energy features of the π⁺ energy spectrum.

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