Kavli Affiliate: T. Higuchi
| First 5 Authors: Belle II Collaboration, I. Adachi, K. Adamczyk, L. Aggarwal, H. Ahmed
| Summary:
We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element
$|V_{cb}|$ from the decay $Bto Dellnu_ell$ using a $365~mathrm{fb}^{-1}$
$e^+e^-toUpsilon(4S)to Bbar B$ data sample recorded by the Belle II
experiment at the SuperKEKB collider. The semileptonic decay of one $B$ meson
is reconstructed in the modes $B^0to D^-(to K^+pi^-pi^-)ell^+nu_ell$ 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
$Upsilon(4S)$ event is not reconstructed explicitly. Using an inclusive
reconstruction of the unobserved neutrino momentum, we determine the recoil
variable $w=v_Bcdot v_D$, 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
$mathcal{B}(B^0to D^-ell^+nu_ell)=(2.06 pm 0.05,(mathrm{stat.}) pm
0.10,(mathrm{sys.}))%$ and $mathcal{B}(B^+tobar D^0ell^+nu_ell)=(2.31
pm 0.04,(mathrm{stat.}) pm 0.09,(mathrm{sys.}))%$. We probe lepton
flavor universality by measuring $mathcal{B}(Bto Denu_e)/mathcal{B}(Bto
Dmunu_mu)=1.020 pm 0.020,(mathrm{stat.})pm 0.022,(mathrm{sys.})$.
Fitting the partial decay branching fraction as a function of $w$ and using the
average of lattice QCD calculations of the $Bto D$ form factor, we obtain $
|V_{cb}|=(39.2pm 0.4,(mathrm{stat.}) pm 0.6,(mathrm{sys.}) pm
0.5,(mathrm{th.})$.
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