Helicity Nonconservation in the Reactiondp→dpπ+π−at 25 GeV/c

We observe the reaction $\mathrm{dp}\to d\left(p{\pi }^{+}{\pi }^{-}\right)$ which allows no exchange of isospin between beam and target particles and therefore may approximate pure diffractive dissociation at this energy. The decay of the $p{\pi }^{+}{\pi }^{-}$ system is not azimuthally isotropic around its direction in the overall c.m. frame, vitiating its interpretation as a fireball. Both $s$- and $t$-channel helicity conservation fail for the process.