$π\to ππ$ results in nuclei

Abstract

The Crystal Ball ($CB$) collaboration at $BNL$ has recently presented results regarding a study of the $π^- A \to π^0π^0 A^\prime$ reaction on $H, D, C, Al$ and $Cu$, using a nearly 4$π$ detector. Similar results, but for the $π^+ A \to π^+π^{\pm} A^\prime$ reaction on $^{2}H$, $^{12}C$, $^{40}Ca$, and $^{208}Pb$, have been published earlier by the $CHAOS$ collaboration at $TRIUMF$. In this Brief Report a comparison of the results of the two measurements is made, which shows that the $CHAOS$ and $CB$ data share relevant common features. In particular, the increase in strength as a function of A seen in the near-threshold $π^+ π^-$ invariant mass spectra reported by the $CHAOS$ group, is also seen in the $π^0 π^0$ CB data, when the results from the two groups are compared in a way which accounts for the different acceptances of the two experiments.