Inclusive $K_S^0{K}_S^0$ Resonance Production in $ep$ Collisions at HERA

Inclusive $K_S^0{K}_S^0$ production in $ep$ collisions at the DESY $ep$ collider HERA was studied with the ZEUS detector using an integrated luminosity of $0.5{\mathrm{fb}}^{-1}$. Enhancements in the mass spectrum were observed and are attributed to the production of $f_2(1270)/a_2^0(1320)$, $f_2^{\prime }(1525)$ and $f_0(1710)$. Masses and widths were obtained using a fit which takes into account theoretical predictions based on SU(3) symmetry arguments, and are consistent with the Particle Data Group values. The $f_0(1710)$ state, which has a mass consistent with a glueball candidate, was observed with a statistical significance of 5 standard deviations. However, if this state is the same as that seen in $\gamma \gamma \to K_S^0{K}_S^0$, it is unlikely to be a pure glueball state.

Figure 1

The measured ${\pi }^{+}{\pi }^{-}$ invariant-mass distribution for events with at least two $K_S^0$ candidates (dots). The shaded area represents the signal window used for $K_S^0{K}_S^0$ pair reconstruction. The fit performed (see text) is displayed as a solid line.

Figure 2

(a) The measured $K_S^0{K}_S^0$ invariant-mass spectrum (dots). The solid line is the result of the fit described as fit 2 in the text [Eq. (3)] and the dashed line represents the background function. (b) Background-subtracted $K_S^0{K}_S^0$ invariant-mass spectrum (dots); the result of the fit is shown as a solid line.

Figure 3

Comparison of the present mass and width measurements of the $f_2^{\prime }(1525)$ and $f_0(1710)$ states with other selected measurements [1]. The bands show the PDG values and error estimates.