Observation of inclusive $D^{*\pm }$ production in the decay of $\mathit{{\rm Y}}(1S)$

We present a study of the inclusive $D^{*\pm }$ production in the decay of $\mathit{{\rm Y}}(1S)$ using $(98.6\pm 0.9)\times {10}^6$ $\mathit{{\rm Y}}(2S)$ mesons collected with the BABAR detector at the $\mathit{{\rm Y}}(2S)$ resonance. Using the decay chain $\mathit{{\rm Y}}(2S)\to {\pi }^{+}{\pi }^{-}\mathit{{\rm Y}}(1S)$, $\mathit{{\rm Y}}(1S)\to D^{*\pm }X$, where $X$ is unobserved, we measure the branching fraction $\mathcal{B}[\mathit{{\rm Y}}(1S)\to D^{*\pm }X]=(2.52\pm 0.13(\mathrm{stat})\pm 0.15(\mathrm{syst}))\%$ and the $D^{*\pm }$ momentum distribution in the rest frame of the $\mathit{{\rm Y}}(1S)$. We find evidence for an excess of $D^{*\pm }$ production over the expected rate from the virtual photon annihilation process $\mathit{{\rm Y}}(1S)\to {\gamma }^{*}\to c\overline{c}\to D^{*\pm }X$.

Figure 1

Distribution of the recoil mass, $M_{\mathrm{recoil}}$, for the selected $\mathit{{\rm Y}}(2S)\to {\pi }^{+}{\pi }^{-}\mathit{{\rm Y}}(1S)$ events. The cross hatching shows the signal region, and the lower and upper sideband regions are indicated by the diagonal shading.

Figure 2

Distribution of the $D^0$ invariant mass for the complete [0.1;1.0] ${\mathrm{x}}_{\mathrm{p}}$ range after subtraction of the combinatoric background and wrong-sign combinations. The solid line represents the fit to the data of the p.d.f. described in the text.

Figure 3

Reconstruction efficiency for the decay chain $\mathit{{\rm Y}}(2S)\to {\pi }^{+}{\pi }^{-}\mathit{{\rm Y}}(1S)$, $\mathit{{\rm Y}}(1S)\to D^{*\pm }X$ as a function of the scaled $D^{*\pm }$ momentum ${\mathrm{x}}_{\mathrm{p}}$.

Figure 4

Signal yield as a function of ${\mathrm{x}}_{\mathrm{p}}$. The solid line represents the expected contribution from the virtual photon process [18].