Evidence for Splitting in the Q Region of K + π + π − Mass

We observe a splitting in the ${K}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ mass spectrum in ${K}^{+}d$ interactions at $9 \frac{\mathrm{GeV}}{c}$. We find a mass of $1243\ifmmode\pm\else\textpm\fi{}8 \frac{\mathrm{MeV}}{{c}^{2}}$ and a width of ${70}_{\ensuremath{-}18}^{+26}$ for the lower mass state, and a mass of 1344 \ifmmode\pm\else\textpm\fi{} 8 and a width of less than $60 \frac{\mathrm{MeV}}{{c}^{2}}$ for the higher mass state. The isospin of both states is determined to be \textonehalf{}. The results can be interpreted as evidence for the mixing of two ${J}^{P}={1}^{+} {K}^{*}$ states.