Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-

Abstract

Using the FOCUS spectrometer with photon beam energies between 20 and 160 \gev, we confirm the existence of a diffractively photoproduced enhancement in $K^{+}{K}^{-}$ at 1750 \mevcc with nearly 100 times the statistics of previous experiments. Assuming this enhancement to be a single resonance with a Breit-Wigner mass shape, we determine its mass to be $1753.5\pm 1.5\pm 2.3$ \mevcc and its width to be $122.2\pm 6.2\pm 8.0$ \mevcc. We find no corresponding enhancement at 1750 \mevcc in $K^{\ast }K$, and again neglecting any possible interference effects we place limits on the ratio $\Gamma (X(1750)\to K^{\ast }K)/\Gamma (X(1750)\to K^{+}{K}^{-})$. Our results are consistent with previous photoproduction experiments, but, because of the much greater statistics, challenge the common interpretation of this enhancement as the $\varphi (1680)$ seen in $e^{+}{e}^{-}$ annihilation experiments.

10 pages, 5 figures