Resonances in $e^{+}{e}^{-}$ annihilation near 2.2 GeV

Using the initial-state radiation method, the $e^{+}{e}^{-}\to K_S{K}_L$ cross section from 1.98 to 2.54 GeV is measured in a data sample of $469{\mathrm{fb}}^{-1}$ collected with the BABAR detector. The results are used in conjunction with previous BABAR results for the $e^{+}{e}^{-}\to K^{+}{K}^{-}$, $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$, $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\eta$, and $e^{+}{e}^{-}\to \omega \pi \pi$ cross sections to investigate the nature of the resonance structure recently observed by the BESIII experiment in the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section.

Figure 1

The $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section measured by BESIII [1] (filled circles) and BABAR [11] (open circles). The curve is the result of the fit to a coherent sum of resonant and nonresonant contributions (see text).

Figure 2

The kinematic-fit ${\chi }^2$ distribution for selected data events with $1.06<m(K_S{K}_L)<2.5\mathrm{GeV}/c^2$ (points with error bars). The hatched histogram represents the simulated background contribution. The solid histogram shows the simulated signal distribution. The vertical lines indicate the boundaries of the signal and control regions.

Figure 3

The $m(K_S{K}_L)$ distribution for data events with ${\chi }^2<10$. The curve represents background estimated from the control region.

Figure 4

Left panel: The measured $e^{+}{e}^{-}\to K_S{K}_L$ cross section fitted with a constant (solid line). The dashed curve represents the resonance line shape with the parameters listed in Table 1. Right panel: The curve is the result of the fit to the $e^{+}{e}^{-}\to K_S{K}_L$ data with a coherent sum of a resonant amplitude with the parameters listed in Table 1 and a nonresonant constant amplitude. The points with error bars represent the data following subtraction of the background, which has been scaled by a factor of 0.94 (see text).

Figure 5

Left panel: The $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ cross section measured by BABAR [9]. Right panel: The $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\eta$ cross section measured by BABAR [16]. The solid curves are the results of the simultaneous fit to the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ and ${\pi }^{+}{\pi }^{-}\eta$ cross section data, while the dashed curves represent the results of the simultaneous fit to the $e^{+}{e}^{-}\to K^{+}{K}^{-}$, ${\pi }^{+}{\pi }^{-}$, and ${\pi }^{+}{\pi }^{-}\eta$ cross section data.

Figure 6

The $e^{+}{e}^{-}\to \omega \pi \pi$ cross section measured by BABAR [8, 18]. The solid curve is the result of the fit by a coherent sum of resonant and nonresonant contributions, while the dashed curve represents the results of the fit to a quadratic polynomial.