Exclusive initial-state-radiation production of the $D\overline{D}$, $D^{*}\overline{D}$, and $D^{*}{\overline{D}}^{*}$ systems

We perform a study of the exclusive production of $D\overline{D}$, $D^{*}$$\overline{D}$, and $D^{*}{\overline{D}}^{*}$ in initial-state-radiation events, from $e^{+}{e}^{-}$ annihilations at a center-of-mass energy near 10.58 GeV, to search for charmonium and possible new resonances. The data sample corresponds to an integrated luminosity of $384{\mathrm{fb}}^{-1}$ and was recorded by the BABAR experiment at the PEP-II storage rings. The $D\overline{D}$, $D^{*}\overline{D}$, and $D^{*}{\overline{D}}^{*}$ mass spectra show clear evidence of several $\psi$ resonances. However, there is no evidence for $Y(4260)\to D^{*}\overline{D}$ or $Y(4260)\to D^{*}{\overline{D}}^{*}$.

Figure 1

$\Delta m$ distributions for $D^{*}\overline{D}$ candidates after applying the $|M_{\mathrm{rec}}^2|<1{\mathrm{GeV}}^2/c^4$ and $m(D^{*}\overline{D})<6\mathrm{GeV}/c^2$ selections, for (a) $D^{*0}\to D^0\gamma$, (b) $D^{*0}\to D^0{\pi }^0$, (c) $D^{*+}\to D^0{\pi }^{+}$ with $D^0\to K^{-}{\pi }^{+}$, and (d) $D^{*+}\to D^{+}{\pi }^0$ with $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$. The shaded regions indicate the ranges used to select the $D^{*}$ candidates.

Figure 2

Distribution of $M_{\mathrm{rec}}^2$, the mass recoiling against the $D^{*}\overline{D}$ system, for (a) $D^{*0}\to D^0\gamma$, (b) $D^{*0}\to D^0{\pi }^0$, and (c) $D^{*+}{D}^{-}$ candidates. The curves are the results from the fits described in the text.

Figure 3

(a) $D^{*0}{\overline{D}}^0$ and (b) $D^{*+}{D}^{-}$ mass spectra. The shaded histogram in (a) is obtained from the $M_{\mathrm{rec}}^2$ sideband region $1.5<M_{\mathrm{rec}}^2<3.5{\mathrm{GeV}}^2/c^4$ normalized to the background estimated from the fit to the $M_{\mathrm{rec}}^2$ distribution. The curve is the result from the fit described in the text.

Figure 4

Cross section for $e^{+}{e}^{-}\to$ (a) $D^{*0}{\overline{D}}^0$, (b) $D^{*+}{D}^{-}$, and (c) $D^{*}\overline{D}$ combined. The error bars correspond to statistical errors only.

Figure 5

$\Delta m$ distributions for $D^{*}{\overline{D}}^{*}$ candidates after applying the $|M_{\mathrm{rec}}^2|<1{\mathrm{GeV}}^2/c^4$ and $m(D^{*}{\overline{D}}^{*})<6\mathrm{GeV}/c^2$ selections, for (a) $D^{*0}\to D^0\gamma$, (b) $D^{*0}\to D^0{\pi }^0$, (c) $D^{*+}\to D^0{\pi }^{+}$ with $D^0\to K^{-}{\pi }^{+}$, and (d) $D^{*+}\to D^{+}{\pi }^0$ with $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$. The shaded regions indicate the ranges used to select the $D^{*}$ signals.

Figure 6

$M_{\mathrm{rec}}^2$ distributions for $D^{*0}{\overline{D}}^{*0}$ for (a) $D^{*0}\to D^0\gamma$, ${\overline{D}}^{*0}\to {\overline{D}}^0\gamma$, (b) $D^{*0}\to D^0{\pi }^0$, ${\overline{D}}^{*0}\to {\overline{D}}^0\gamma$, and (c) $D^{*0}\to D^0{\pi }^0$, ${\overline{D}}^{*0}\to {\overline{D}}^0{\pi }^0$.

Figure 7

$M_{\mathrm{rec}}^2$ distributions for (a) $D^{*0}{\overline{D}}^{*0}$ and (b) $D^{*+}{D}^{*-}$. The curve in (a) is the result from the fit described in the text.

Figure 8

$D^{*}{\overline{D}}^{*}$ mass spectrum. The shaded histogram is obtained from the $M_{\mathrm{rec}}^2$ sidebands $-2.5<M_{\mathrm{rec}}^2<-1.5$ and $1.5<M_{\mathrm{rec}}^2<2.5{\mathrm{GeV}}^2/c^4$. The curve is the result from the fit described in the text.

Figure 9

Cross section $e^{+}{e}^{-}\to D^{*}{\overline{D}}^{*}$ for combined $D^{*0}{\overline{D}}^{*0}$ and $D^{*+}{D}^{*-}$. Error bars indicate the statistical errors only.

Figure 10

$M_{\mathrm{rec}}^2$ distribution for (a) $D^0{\overline{D}}^0$ and (b) $D^{+}{D}^{-}$. The curves are the results from the fits described in the text.

Figure 11

$D\overline{D}$ mass distribution. The shaded histogram is obtained from the $M_{\mathrm{rec}}^2$ sideband. The curve is the result from the fit described in the text.

Figure 12

Fits to the (a) $D\overline{D}$, (b) $D^{*}\overline{D}$, and (c) $D^{*}{\overline{D}}^{*}$ mass spectra. Data are represented with error bars, the curves represent the fitted functions. The shaded histogram corresponds to the smoothed incoherent background ($B(m)$) estimated from sidebands. The second smooth solid line represents the nonresonant contribution ($|P(m){|}^2$).

Figure 13

Sum of $e^{+}{e}^{-}\to D\overline{D}$, $e^{+}{e}^{-}\to D^{*}\overline{D}$, and $e^{+}{e}^{-}\to D^{*}{\overline{D}}^{*}$ cross sections. The arrow indicates the position of the $Y(4260)$.