$\overline{K}K$ system in ${\pi }^{-}p\to K^{-}{K}^{+}n$ at 6 GeV/c

The reaction ${\pi }^{-}p\to K^{-}{K}^{+}n$ has been studied at 6 GeV/c with a 16 000 event data sample obtained with the Argonne National Laboratory Effective Mass Spectrometer. Moments of the $K^{-}{K}^{+}$ decay angular distributions are shown as functions of the $K^{-}{K}^{+}$ effective mass from threshold to 1500 MeV, and as functions of momentum transfer from $t_{min}$ to -0.4 ${\mathrm{GeV}}^2$. The $t$-channel moments $〈Y_l^m〉$ with $m=0\mathrm{}$ dominate over the $m=1\mathrm{}$ moments, while moments with $m\ge 2$ (and those with $l\ge 6$) are negligible; this indicates that the dominant $t$-channel exchange production amplitudes have helicity zero at the meson vertex. The slope of $\frac{d\sigma }{\mathrm{dt}}$ decreases as the $K^{-}{K}^{+}$ mass increases. There is a broad $D$-wave enhancement near 1350 MeV. Interfering $f$ and $A_2^0$ $D$-wave Breit-Wigner resonances are not sufficient to explain all of the $Y_4^0$ distribution above 1350 MeV and an additional $D$-wave contribution may be present. Ignoring this complication, the best $f-A_2^0$ fit to the $Y_4^0$ spectrum yields a branching ratio $\frac{(f\to \overline{K}K)}{(f\to \mathrm{all})}=(3.1\mathrm{}\pm 1.0)\%$.