Observation and study of the baryonic $B$-meson decays $B\to D^{(*)}p\overline{p}(\pi )(\pi )$

We present results for $B$-meson decay modes involving a charm meson, protons, and pions using $455\times {10}^6$ $B\overline{B}$ pairs recorded by the BaBar detector at the SLAC PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The branching fractions are measured for the following ten decays: ${\overline{B}}^0\to D^{0}p\overline{p}$, ${\overline{B}}^0\to D^{*0}p\overline{p}$, ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$, $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$, ${\overline{B}}^0\to D^{0}p\overline{p}{\pi }^{-}{\pi }^{+}$, ${\overline{B}}^0\to D^{*0}p\overline{p}{\pi }^{-}{\pi }^{+}$, $B^{-}\to D^{+}p\overline{p}{\pi }^{-}{\pi }^{-}$, and $B^{-}\to D^{*+}p\overline{p}{\pi }^{-}{\pi }^{-}$. The four $B^{-}$ and the two five-body ${\overline{B}}^0$ modes are observed for the first time. The four-body modes are enhanced compared to the three- and the five-body modes. In the three-body modes, the $M(p\overline{p})$ and $M(D^{(*)0}p)$ invariant-mass distributions show enhancements near threshold values. In the four-body mode ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, the $M(p{\pi }^{-})$ distribution shows a narrow structure of unknown origin near $1.5\mathrm{GeV}/c^2$. The distributions for the five-body modes, in contrast to the others, are similar to the expectations from uniform phase-space predictions.

Figure 1

Typical quarkline diagrams representing (a) ${\overline{B}}^0\to D^{(*)0}p\overline{p}$ and (b) $B^{-}\to D^{(*)0}p\overline{p}{\pi }^{-}$ modes. The gluon lines are omitted.

Figure 2

Event display for the candidate decay $B^0\to {\overline{D}}^{0}p\overline{p}$, ${\overline{D}}^0\to K^{+}{\pi }^{-}$. The labeled tracks in the tracking system and DIRC rings at the perimeter correspond to the particles in the reconstructed decay chain. The remaining unlabeled tracks and rings are due to the decay of the other ${\overline{B}}^0$ meson in the event. The beam axis is perpendicular to the image.

Figure 3

Scatter plots of $M_{\mathrm{ES}}-\Delta E$ for the six newly observed $B$-meson decay modes: (a) $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, (b) ${\overline{B}}^0\to D^{0}p\overline{p}{\pi }^{-}{\pi }^{+}$, (c) $B^{-}\to D^{+}p\overline{p}{\pi }^{-}{\pi }^{-}$, (d) $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$, (e) ${\overline{B}}^0\to D^{*0}p\overline{p}{\pi }^{-}{\pi }^{+}$, and (f) $B^{-}\to D^{*+}p\overline{p}{\pi }^{-}{\pi }^{-}$. The first row of plots is related to the second by the exchange of the charm meson $D\leftrightarrow D^{*}$. The decay chain involving $D^0\to K^{-}{\pi }^{+}$ or $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ is shown. For (d, e, f), the decay chain involves $D^{*0}\to D^0{\pi }^0$ or $D^{*+}\to D^0{\pi }^{+}$. The $M_{\mathrm{ES}}$ projection, in $1\mathrm{MeV}/c^2$ bins, is given above the scatter plot; the $\Delta E$, in 1 MeV bins, on the right. For the projection plots, no selection is made on the complementary variable.

Figure 4

Fit details for $B^{-}\to D^{+}p\overline{p}{\pi }^{-}{\pi }^{-}$, $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$: $M_{\mathrm{ES}}$ and $\Delta E$ distributions in regions as noted on the plots. For (a, c) the top curve is the sum of $P_{\mathrm{sig}}$ and $P_{\mathrm{bgd}}$ and the bottom curve is the latter; for (b, d) the curve is $P_{\mathrm{bgd}}$.

Figure 5

$M_{\mathrm{ES}}$ fit projections for the three-body modes: (a–c) ${\overline{B}}^0\to D^{0}p\overline{p}$ and (d–f) ${\overline{B}}^0\to D^{*0}p\overline{p}$, where (a, d) are reconstructed via $D^0\to K^{-}{\pi }^{+}$, (b, e) $D^0\to K^{-}{\pi }^{+}{\pi }^0$, and (c, f) $D^0\to K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$; and (d–f) $D^{*0}\to D^0{\pi }^0$. Events with $\Delta E$ within $2.5\sigma$ of the mean value of the Gaussian function are shown. The top curve is the sum of $P_{\mathrm{sig}}$ and $P_{\mathrm{bgd}}$ and the bottom curve is the latter.

Figure 6

$M_{\mathrm{ES}}$ fit projections for the four-body modes: (a) ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, (b–d) ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$, (e–g) $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, and (h–j) $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$, where (a) is reconstructed via $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$, (b, e, h) $D^0\to K^{-}{\pi }^{+}$, (c, f, i) $D^0\to K^{-}{\pi }^{+}{\pi }^0$, and (d, g, j) $D^0\to K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$; and (b–d) $D^{*+}\to D^0{\pi }^{+}$ and (h–j) $D^{*0}\to D^0{\pi }^0$. Events with $\Delta E$ within $2.5\sigma$ of the Gaussian mean value are shown. For (a–g) the top curve is the sum of $P_{\mathrm{sig}}$ and $P_{\mathrm{bgd}}$ and the bottom curve is the latter; for (h–j) the middle curve is the sum of $P_{\mathrm{peak}}$ and $P_{\mathrm{bgd}}$.

Figure 7

$M_{\mathrm{ES}}$ fit projections for the five-body modes: (a–c) ${\overline{B}}^0\to D^{0}p\overline{p}{\pi }^{-}{\pi }^{+}$, (d–f) ${\overline{B}}^0\to D^{*0}p\overline{p}{\pi }^{-}{\pi }^{+}$, (g) $B^{-}\to D^{+}p\overline{p}{\pi }^{-}{\pi }^{-}$, and (h–j) $B^{-}\to D^{*+}p\overline{p}{\pi }^{-}{\pi }^{-}$, where (a, d, h) are reconstructed via $D^0\to K^{-}{\pi }^{+}$, (b, e, i) $D^0\to K^{-}{\pi }^{+}{\pi }^0$, (c, f, j) $D^0\to K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$, and (g) $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$; and (b–d) $D^{*+}\to D^0{\pi }^{+}$ and (h–j) $D^{*0}\to D^0{\pi }^0$. Events with $\Delta E$ within $2.5\sigma$ of the Gaussian mean value are shown. The top curve is the sum of $P_{\mathrm{sig}}$ and the $P_{\mathrm{bgd}}$ and the bottom curve is the latter. We note that the plots in (b, c, e, f) had difficulties with fit convergence; see text.

Figure 8

Dalitz plots $M^2(p\overline{p})$ vs $M^2(D^{(*)0}p)$ for the three-body modes. Plots in the first column (a, c) correspond to ${\overline{B}}^0\to D^{0}p\overline{p}$; the second column (b, d) ${\overline{B}}^0\to D^{*0}p\overline{p}$. Plots in the first row (a, b) are the events in the $M_{\mathrm{ES}}-\Delta E$ signal box; the second row (c, d) the events in the $M_{\mathrm{ES}}$-sideband region normalized to the amount of background present in the respective plots in the first row. In the first row, near-threshold enhancements are seen compared to the respective sideband plots in the second row. The lines drawn at $M^2(p\overline{p})=5$, $M^2(D^{0}p)=9$, and $M^2(D^{*0}p)=10.5{\mathrm{GeV}}^2/c^4$ are visual aides to show that the enhancements are mostly nonoverlapping. The events are contained in the shaded contour representing the allowed kinematic region except for one outlier in (d), which failed the fit. The points are made larger for the plots in the second column for better visibility.

Figure 9

Differential branching fraction plots for the three-body $B$-meson modes: (a–d) ${\overline{B}}^0\to D^{0}p\overline{p}$ and (e–h) ${\overline{B}}^0\to D^{*0}p\overline{p}$. The captions give the various phase-space regions. The shaded region represents the uniform phase-space model with its area normalized to the data. The bin width for each row of plots is given on the leftmost plot.

Figure 10

Differential branching fraction plots as functions of $M(p\overline{p})$, $M(D^{(*)}p)$, $M(D^{(*)}\overline{p})$, and $M(p{\pi }^{-})$ for the four-body $B$-meson modes: (a, b, c, d) ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, (e, f, g, h) ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$, (i, j, k, l) $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, and (m, n, o, p) $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$, respectively. The shaded region represents the uniform phase-space model normalized to the data. The possible presence of a narrow peak near $1.5\mathrm{GeV}/c^2$ in plots in (d, h, j, p) are shown in detail in Figs. 12, respectively, and discussed in Sec. 6d. The bin width for each row of plots is given on the left.

Figure 11

Differential branching fraction plots as functions of $M(p\overline{p})$, $M(D^{(*)}p)$, $M(D^{(*)}\overline{p})$, and $M(p{\pi }^{-})$ for five-body $B$-meson modes: (a, b, c, d) ${\overline{B}}^0\to D^{0}p\overline{p}{\pi }^{-}{\pi }^{+}$, (e, f, g, h) ${\overline{B}}^0\to D^{*0}p\overline{p}{\pi }^{-}{\pi }^{+}$, (i, j, k, l) $B^{-}\to D^{+}p\overline{p}{\pi }^{-}{\pi }^{-}$, and (m, n, o, p) $B^{-}\to D^{*+}p\overline{p}{\pi }^{-}{\pi }^{-}$, respectively. The shaded region represents the uniform phase-space model normalized to the data. Each $B$-meson candidate for the plots in (d, h) contributes two entries for both $p{\pi }^{-}$ and $\overline{p}{\pi }^{+}$ combinations, so they are scaled accordingly. The bin width for each row of plots is given on the left.

Figure 12

Fits of the opposite-sign $M(p{\pi }^{-})$ distribution for (a) ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, (b) ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$, (c) $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, and (d) $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$ for events in the signal box of $M_{\mathrm{ES}}$-$\Delta E$. The top curve is the sum of $P_{\mathrm{sig}}$ and $P_{\mathrm{bgd}}$ while the bottom curve is $P_{\mathrm{bgd}}$. The $P_{\mathrm{bgd}}$ is from the corresponding plot in Fig. 13. The shaded histograms are scaled $M_{\mathrm{ES}}$ sidebands. A small inset plot is a close-up of the region around $1.5\mathrm{GeV}/c^2$; its bin width is the same as in the larger plot.

Figure 13

Fits of the same-sign $M(\overline{p}{\pi }^{-})$ distribution for (a) ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$, (b) ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$, (c) $B^{-}\to D^{0}p\overline{p}{\pi }^{-}$, and (d) $B^{-}\to D^{*0}p\overline{p}{\pi }^{-}$ for events in the signal box of $M_{\mathrm{ES}}$-$\Delta E$. The curve is the smoothed histogram that is used in the corresponding plot in Fig. 12 as $P_{\mathrm{bgd}}$. The shaded histograms are scaled $M_{\mathrm{ES}}$ sidebands.

Figure 14

Alternate fits of the opposite-sign $M(p{\pi }^{-})$ distribution for ${\overline{B}}^0\to D^{+}p\overline{p}{\pi }^{-}$ with (a) various $N^{*}$ resonances and (b) an additional $P_{\mathrm{bgd}}$ obtained from the ${\overline{B}}^0\to D^{*+}p\overline{p}{\pi }^{-}$ sample. The shaded histograms are the scaled $M_{\mathrm{ES}}-\Delta E$ sidebands. A small inset plot is a close-up of the region around $1.5\mathrm{GeV}/c^2$; its bin width is the same as the larger plot.