Effect of Background on theI=2ππScattering Phase Shifts

Abstract

We show that in the reaction ${\pi }^{-}p\to {\pi }^{-}{\pi }^{-}{\pi }^{+}p$ at 3.9 GeV/c, the peaking in the ${\pi }^{-}{\pi }^{-}$ "scattering angular distribution" above 0.6-GeV c.m. energy inferred from the one-pion exchange model can be interpreted as resulting from a background of competing processes. Similar background effects may be significant also in the reaction ${\pi }^{+}p\to {\pi }^{+}{\pi }^{+}n$, and conclusions from that reaction as to evidence for $d$ waves in the $I=2\mathrm{}$ amplitude below 1 GeV should be reserved pending a similar analysis.