Search for Backward $A_1$ and $A_2$ Production in ${\pi }^{-}p\to p{\pi }^{-}{\pi }^{+}{\pi }^{-}$ at 8 GeV/c

Backward meson production in the reaction ${\pi }^{-}p\to p{\pi }^{-}{\pi }^{+}{\pi }^{-}$ has been studied with use of a streamer chamber triggered by the detection of a fast forward proton. For ${cos\theta }^{*}<-0.98\mathrm{}$ we find no evidence of $A_1$ or $A_2$ production, and we determine total backward cross-section upper limits (95% confidence) of 0.93 and 0.72 μb, respectively. At $m_{3\pi }=1.9\mathrm{}$ GeV/${\mathit{c}}^2$ we observe a broad enhancement of about 3-standard-deviation significance. Evidence for backward quasi-two-body production is seen in the ${\rho }^{0}p{\pi }^{-}$ and $f^{0}p{\pi }^{-}$ channels.