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

Le résumé fourni par la source

We have studied backward baryon and meson production in ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ 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 ${N}^{*}\ensuremath{\rho}$ 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 ${N}^{*}\ensuremath{\rho}$ and ${N}^{*}f$ intermediate states is consistent with $u$-channel proton exchange as the dominant production mechanism. In the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ mass distribution we observe a 3- to 4- standard-deviation enhancement at ${M}_{3\ensuremath{\pi}}=1897\ifmmode\pm\else\textpm\fi{}17$ MeV/${\mathit{c}}^{2}$ with full width at half maximum = 110 \ifmmode\pm\else\textpm\fi{} 82 MeV/${\mathit{c}}^{2}$, but find no but find no evidence for backward ${A}_{1}$ or ${A}_{2}$ production. We observe ${\ensuremath{\Delta}}^{++}(1232)$ production in the $p{\ensuremath{\pi}}^{+}$ effective mass distribution.

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