Polarization effects in rho 0-meson production in antiproton-proton interactions at 22.4, 12, and 5.7 GeV/c.

Abstract

The ${\ensuremath{\rho}}^{0}$-meson spin alignment is studied in $\overline{p}p$ interactions at 22.4 and 12 GeV/c and in the reaction $\overline{p}p\ensuremath{\rightarrow}2{\ensuremath{\pi}}^{+}+2{\ensuremath{\pi}}^{\ensuremath{-}}+\mathrm{neutrals}$ at 5.7 GeV/c. An essential ${\ensuremath{\rho}}^{0}$-meson spin alignment is observed. The values of the ${\ensuremath{\rho}}_{00}^{T}$ element of the ${\ensuremath{\rho}}^{0}$-meson spin-density matrix in the transversity frame are 0.56 \ifmmode\pm\else\textpm\fi{} 0.07, 0.53 \ifmmode\pm\else\textpm\fi{} 0.05, and 0.54 \ifmmode\pm\else\textpm\fi{} 0.04 for the above-mentioned interactions, respectively. An increase of ${\ensuremath{\rho}}_{00}^{T}$ with ${\ensuremath{\rho}}^{0}$ transverse momentum is obtained.