Measurement of the form factors of the decay B0 -> D*- ell+ nu and determination of the CKM matrix element |Vcb|

This article describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ from the decay $B^0\to D^{\ast -}{\mathrm{\ell }}^{+}{\nu }_{\mathrm{\ell }}$ using 711 fb${}^{-1}$ of Belle data collected near the $\mathrm{{\rm Y}}(4S)$ resonance. We simultaneously measure the product of the form factor normalization $\mathcal{F}(1)$ and the matrix element $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ as well as the three parameters ${\rho }^2$, $R_1(1)$ and $R_2(1)$, which determine the form factors of this decay in the framework of the Heavy Quark Effective Theory. The results, based on about 120,000 reconstructed $B^0\to D^{\ast -}{\mathrm{\ell }}^{+}{\nu }_{\mathrm{\ell }}$ decays, are ${\rho }^2=1.214\pm 0.034\pm 0.009$, $R_1(1)=1.401\pm 0.034\pm 0.018$, $R_2(1)=0.864\pm 0.024\pm 0.008$ and $$\mathcal{F}$(1)|V_{cb}|=(34.6\pm 0.2\pm 1.0)\times 10^{-3}$\mathrm{.}Thebranchingfractionof$B^0\to D^{-}\ell^+\nu_\ell$ is measured at the same time; we obtain a value of $$\mathcal{B}$(B^0 \to D^{-}\ell^+ \nu_\ell) = (4.58 \pm 0.03 \pm 0.26) %$. The errors correspond to the statistical and systematic uncertainties. These results give the most precise determination of the form factor parameters and $\mathcal{F}(1)\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ to date. In addition, a direct, model-independent determination of the form factor shapes has been carried out.