Observation of new resonances decaying to $D\pi$ and $D^{*}\pi$ in inclusive $e^{+}{e}^{-}$ collisions near $\sqrt{s}=10.58\mathrm{GeV}$

We present a study of the $D^{+}{\pi }^{-}$, $D^0{\pi }^{+}$, and $D^{*+}{\pi }^{-}$ systems in inclusive $e^{+}{e}^{-}\to c\overline{c}$ interactions in a search for new excited $D$ meson states. We use a data set, consisting of $\sim 454{\mathrm{fb}}^{-1}$, collected at center-of-mass energies near 10.58 GeV by the BABAR detector at the SLAC PEP-II asymmetric-energy collider. We observe, for the first time, candidates for the radial excitations of the $D^0$, $D^{*0}$, and $D^{*+}$, as well as the $L=2$ excited states of the $D^0$ and $D^{+}$, where $L$ is the orbital angular momentum of the quarks.

Figure 1

Mass distribution for (a) $D^{+}$ and (b) $D^0$ candidates in the $D^{+}{\pi }^{-}$ and $D^0{\pi }^{+}$ samples. Plots (c) and (d) correspond to the $D^{*+}{\pi }^{-}$ sample and show the mass distribution for $D^0$ candidates and the $\Delta m$ distribution for $D^{*+}$ candidates. The vertical lines show the signal and, in (a) and (b), the sideband regions.

Figure 2

Mass distribution for $D^{+}{\pi }^{-}$ (top) and $D^0{\pi }^{+}$ (bottom) candidates. Points correspond to data, with the total fit overlaid as a solid curve. The dotted curves are the signal components. The lower solid curves correspond to the smooth combinatoric background and to the peaking backgrounds at $2.3\mathrm{GeV}/c^2$. The inset plots show the distributions after subtraction of the combinatoric background.

Figure 3

Mass distributions for $D^{*+}{\pi }^{-}$ candidates. Top: candidates with $|\cos {\theta }_H|>0.75$. Middle: candidates with $|\cos {\theta }_H|<0.5$. Bottom: all candidates. Points correspond to data, with the total fit overlaid as a solid curve. The lower solid curve is the combinatoric background, and the dotted curves are the signal components. The inset plots show the distributions after subtraction of the combinatoric background.

Figure 4

Distribution in $\cos {\theta }_H$ for each signal in $D^{*+}{\pi }^{-}$. The error bars include statistical and correlated systematic uncertainties. The curve is a fit using the function $Y$ shown in the plot; ${\epsilon }_H$ is the efficiency as a function of $\cos {\theta }_H$.