Measurement of the form factors of the decay B^0 -> D^{*-} l^+ nu_l and determination of the CKM matrix element |V_{cb}|

This paper describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ using the decay $B^0\to D^{\ast -}{\mathrm{\ell }}^{+}{\nu }_{\mathrm{\ell }}$. We perform a combined measurement of this quantity and of the form factors ${\rho }^2$, $R_1(1)$, and $R_2(1)$ which fully characterize this decay in the framework of heavy-quark effective theory, based on 140 fb${}^{-1}$ of Belle data collected near the $\mathrm{{\rm Y}}(4S)$ resonance. The results, based on about 69,000 reconstructed $B^0\to D^{\ast -}{\mathrm{\ell }}^{+}{\nu }_{\mathrm{\ell }}$ decays, are $\rho^2=1.293\pm 0.045\pm 0.029$,$R_1(1)=1.495\pm 0.050\pm 0.062$,$R_2(1)=0.844\pm 0.034\pm 0.019$and$$\mathcal{F}$(1)|V_{cb}|=34.4\pm 0.2\pm 1.0$\mathrm{.}The$B^0\to D^{*-}\ell^+\nu_\ell$branchingfractionisfoundtobe$(4.42\pm 0.03\pm 0.25)%$. For all these numbers, the first error is the statistical and the second is the systematic uncertainty. All results are preliminary.