Measurement of Semileptonic Branching Fractions of $B$ Mesons to Narrow $D^{**}$ States

Using the data accumulated in 2002–2004 with the D0 detector in proton-antiproton collisions at the Fermilab Tevatron collider with a center-of-mass energy of 1.96 TeV, the branching fractions of the decays $B\to {\overline{D}}_1^0(2420){\mu }^{+}{\nu }_{\mu }X$ and $B\to {\overline{D}}_2^{*0}(2460){\mu }^{+}{\nu }_{\mu }X$ and their ratio have been measured: $\mathcal{B}(\overline{b}\to B)\times \mathcal{B}(B\to {\overline{D}}_1^0{\mu }^{+}{\nu }_{\mu }X)\times \mathcal{B}({\overline{D}}_1^0\to D^{*-}{\pi }^{+})=[0.087\pm 0.007(\mathrm{stat})\pm 0.014(\mathrm{syst})]\%$; $\mathcal{B}(\overline{b}\to B)\times \mathcal{B}(B\to {\overline{D}}_2^{*0}{\mu }^{+}{\nu }_{\mu }X)\times \mathcal{B}({\overline{D}}_2^{*0}\to D^{*-}{\pi }^{+})=[0.035\pm 0.007(\mathrm{stat})\pm 0.008(\mathrm{syst})]\%$ and $[\mathcal{B}(B\to {\overline{D}}_2^{*0}{\mu }^{+}{\nu }_{\mu }X)\times \mathcal{B}({\overline{D}}_2^{*0}\to D^{*-}{\pi }^{+})]/[\mathcal{B}(B\to {\overline{D}}_1^0{\mu }^{+}{\nu }_{\mu }X)\times \mathcal{B}({\overline{D}}_1^0\to D^{*-}{\pi }^{+})]=0.39\pm 0.09(\mathrm{stat})\pm 0.12(\mathrm{syst})$, where the charge conjugated states are always implied.

Figure 1

Distribution of the mass difference $M(K\pi \pi )-M(K\pi )$ for events with $1.75<M(K\pi )<1.95\mathrm{GeV}/c^2$. The fit function describes the signal as the sum of two Gaussian functions and the background as the sum of exponential and first-order polynomial functions. The signal contribution is also shown separately. The hatched histogram corresponds to the same-sign combination of the muon and pion charges.

Figure 2

The invariant mass $M(D^{*}\pi )$. Event selection is described in the text. The points correspond to the $D^{*}\pi$ combinations with opposite charges, and the hatched histogram corresponds to the same-charge combinations. The distribution was fit with a sum of two relativistic Breit-Wigner functions corresponding to two narrow $D^{**}$ states and a second-order polynomial describing the background. The contributions of $D_1^0$ and $D_2^{*0}$ to the fit are shown separately.