Charged Pion Production from Neutron--proton Collisions at 790 MeV. [Differential Cross Sections, Symmetry]. PDF Download

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The two reactions np .-->. nn.pi. and np .-->. pp.pi.− were studied at 790 MeV (incident neutron energy). Pion spectra were measured at 10 different angles with a multiwire proportional chamber spectrometer. Approximately 100,000 events were analyzed. The angular distribution of pions in the np center of momentum system (d sigma/d.cap omega.*) was given by ((123.1 +- 2.7) + (88.3 +- 4.9)cos2(theta*))(.mu.b/sr). The cross section sigma(np .-->. NN.pi./sup +-/) was determined to be 1.92 +- 20 mb by integrating (d sigma/d.cap omega.*) over all angles. The partial cross section for pion production from T = 0 np interactions (sigma01) was found to be .1/sub -.1//sup +.5/ mb by using the relation sigma01 = 2sigma(np .-->. NN.pi./sup +- )--sigma(pp .-->. pp.pi.°). Stronger indications of nonresonant pion production were given by the presence of asymmetries between the positive and negative pion spectra and a comparison of the data with an isobar model calculation.