Measurement of the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section in the energy range $\sqrt{s}=1.05-2.0\mathrm{GeV}$

The $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section is measured in the center-of-mass energy range 1.05–2.00 GeV at the SND detector. The measurement is based on data with an integrated luminosity of $35{\mathrm{pb}}^{-1}$ collected at the VEPP-2000 $e^{+}{e}^{-}$-collider. The obtained results are consistent with the previous most accurate data obtained in the BABAR experiment and have a comparable accuracy.

Figure 1

The two-dimensional $\mathrm{\Delta }\varphi$ vs $\mathrm{\Delta }\theta$ distribution for selected data events with $\sqrt{s}=1.4–1.6\mathrm{GeV}$. The dashed lines indicate the boundaries of the conditions on $\mathrm{\Delta }\varphi$ and $\mathrm{\Delta }\theta$. The central box is a signal region corresponding to the standard selection criteria for $e^{+}{e}^{-}\to K^{+}{K}^{-}$ candidates.

Figure 2

The distribution of the normalized total energy deposition in the calorimeter for selected data events with $\sqrt{s}=1.4–1.6\mathrm{GeV}$ (points with error bars). The shaded histogram represents the noncollinear background. The dotted, dashed, and dash-dotted curves show the contribution of $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ and cosmic events, $e^{+}{e}^{-}\to K^{+}{K}^{-}$ events, and $e^{+}{e}^{-}\to e^{+}{e}^{-}$ events, respectively. The solid curve is the sum of these three components.

Figure 3

The distribution of the normalized total energy deposition in the calorimeter for data events with $\sqrt{s}=1.4–1.6\mathrm{GeV}$ selected with the additional requirement that the muon system fires (points with error bars). The shaded histogram represents the noncollinear background. The descriptions of the curves are given in the caption of Fig. 2.

Figure 4

The distribution of the normalized total energy deposition in the calorimeter for data events with $\sqrt{s}=1.4–1.6\mathrm{GeV}$ in which the condition of no ACC signal is applied to both particles (points with error bars). The shaded histogram represents the noncollinear background. The descriptions of the curves are given in the caption of Fig. 2.

Figure 5

The energy dependence of the detection efficiency for $e^{+}{e}^{-}\to K^{+}{K}^{-}$ events with $E_{\gamma }=0$.

Figure 6

The dependence of the detection efficiency on the energy of the photon emitted from the initial state at $\sqrt{s}=1.6\mathrm{GeV}$.

Figure 7

The Born cross section for the process $e^{+}{e}^{-}\to K^{+}{K}^{-}$ measured in this work and in the BABAR experiment [12]. The curve is the result of the fit described in the text.

Figure 8

The relative difference between the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section measured in the BABAR experiment [12] and the fit to SND data shown in Fig. 7. For BABAR data (points with error bars), the statistical errors (diagonal elements of the covariance matrix) are shown. The shaded band represents the SND and BABAR systematic uncertainties combined in quadrature. The BABAR systematic uncertainty is 1.49% at $\sqrt{s}=1.05–1.10\mathrm{GeV}$, 1.64% at $\sqrt{s}=1.1–1.2\mathrm{GeV}$, 2.23% at $\sqrt{s}=1.2–1.3\mathrm{GeV}$, 3.37% at $\sqrt{s}=1.3–1.5\mathrm{GeV}$, 3.73% at $\sqrt{s}=1.5–1.7\mathrm{GeV}$, and 7.03% above 1.7 GeV.