Backward production inπ−p→pπ+π−π−at 8 GeV/c

Abstract

We have studied backward baryon and meson production in ${\pi }^{-}p\to p{\pi }^{+}{\pi }^{-}{\pi }^{-}$ at 8.0 GeV/c using a streamer chamber triggered by the detection of a fast forward proton. Our data sample (1227 events) displays prominent $N^{*}\rho$ and $N^{*}f$ quasi-two-body production. These states are investigated with regard to the peripheral nature of the production mechanism and sequential decay of the excited baryon and meson systems. The quasi-two-body production of $N^{*}\rho$ and $N^{*}f$ intermediate states is consistent with $u$-channel proton exchange as the dominant production mechanism. In the ${\pi }^{+}{\pi }^{-}{\pi }^{-}$ mass distribution we observe a 3- to 4- standard-deviation enhancement at $M_{3\pi }=1897\mathrm{}\pm 17$ MeV/${\mathit{c}}^2$ with full width at half maximum = 110 ± 82 MeV/${\mathit{c}}^2$, but find no but find no evidence for backward $A_1$ or $A_2$ production. We observe ${\Delta }^{++}\mathrm{}\left(1232\right)\mathrm{}$ production in the $p{\pi }^{+}$ effective mass distribution.