Study ofνdcharged-current two-pion production in the threshold region

We present our final results on double-pion production by muon-type neutrinos observed in a 2.4×${10}^6$ (365 000) picture exposure of the Argonne 12-foot deuterium- (hydrogen-) filled bubble chamber. The reactions $\nu d\to {\mu }^{-}{\pi }^{-}{\pi }^{+}p{p}_s$, $\nu d\to {\mu }^{-}{\pi }^{+}{\pi }^{0}p{n}_s$, and $\nu d\to {\mu }^{-}{\pi }^{+}{\pi }^{+}n{n}_s$ are studied. The data, which shows strong $\Delta \mathrm{}\left(1236\right)\mathrm{}$ production, has nucleon-$\pi -\pi$ mass distribution peaked at low masses in all three reactions. The excitation functions for the three reactions exhibit a rapid rise over the energy range from threshold up to about 3 GeV, but thereafter the energy dependence appears less pronounced. The threshold behavior of the cross sections for these reactions is analyzed in the context of a model developed by Adjei, Dicus, and Teplitz. Data from the constrained reaction, $\nu d\to {\mu }^{-}{\pi }^{-}{\pi }^{+}p{p}_s$, satisfy the Adler conserved-vector-current test.