Determination of $|V_{cb}|$ using $B\to D\ell {\nu }_{\ell }$ Decays at Belle II

Abstract

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from the decay $B\to D\ell {\nu }_{\ell }$ using a $365{\mathrm{fb}}^{-1}$ $e^{+}{e}^{-}\to {\rm Y}(4S)\to B\bar{B}$ data sample recorded by the Belle II experiment at the SuperKEKB collider. The semileptonic decay of one $B$ meson is reconstructed in the modes $B^0\to D^{-}(\to K^{+}{\pi }^{-}{\pi }^{-}){\ell }^{+}{\nu }_{\ell }$ and $B^{+}\to {\bar{D}}^0(\to K^{+}{\pi }^{-}){\ell }^{+}{\nu }_{\ell }$, where $\ell$ denotes either an electron or a muon. Charge conjugation is implied. The second $B$ meson in the ${\rm Y}(4S)$ event is not reconstructed explicitly. Using an inclusive reconstruction of the unobserved neutrino momentum, we determine the recoil variable $w=v_B\cdot v_D$, where $v_B$ and $v_D$ are the 4-velocities of the $B$ and $D$ mesons. We measure the total decay branching fractions to be $\mathcal{B}(B^0\to D^{-}{\ell }^{+}{\nu }_{\ell })=(2.06\pm 0.05(stat.)\pm 0.10(sys.))\%$ and $\mathcal{B}(B^{+}\to {\bar{D}}^0{\ell }^{+}{\nu }_{\ell })=(2.31\pm 0.04(stat.)\pm 0.09(sys.))\%$. We probe lepton flavor universality by measuring $\mathcal{B}(B\to De{\nu }_e)/\mathcal{B}(B\to D\mu {\nu }_{\mu })=1.020\pm 0.020(stat.)\pm 0.022(sys.)$. Fitting the partial decay branching fraction as a function of $w$ and using the average of lattice QCD calculations of the $B\to D$ form factor, we obtain $|V_{cb}|=(39.2\pm 0.4(stat.)\pm 0.6(sys.)\pm 0.5(th.))\times 10^{-3}$.

References in corpus (3)

• Evidence for $B^{+}\to K^{+}\nu \bar{\nu }$ decays
• Measurement of Differential Distributions of $B\to D^{\ast }\ell {\bar{\nu }}_{\ell }$ and Implications on $|V_{cb}|$
• Determination of $|V_{cb}|$ using ${\overline{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with Belle II