Measurements of the B to D* Form Factors Using the Decay B0 --> D* e nu_e

Abstract

We measure the dependence of $\bar B^0 \to D^{*+}e^-\barν_e$ on the decay angles and momentum transfer. The data sample consists of $\sim 86 \times 10^6$ $B\bar B$-pairs accumulated on the $Υ(4{\rm S})$ resonance by the BABAR detector at the asymmetric $e^+ e^-$ collider PEP-II. We specify the three form factors by two ratios $R_1$ and $R_2$, and by a single parameter $ρ^2$ characterizing the polynomial representing $h_{A_1}$, the function which describes the momentum-transfer dependence of the form factor $A_1$. We determine $R_1$, $R_2$, and $ρ^2$ using an unbinned maximum likelihood fit to the full decay distribution. The results are $R_1=1.396\pm 0.060\pm 0.035\pm 0.027$, $R_2=0.885\pm 0.040\pm 0.022\pm 0.013$, and $ρ^2=1.145\pm 0.059\pm 0.030\pm 0.035$. The stated uncertainties are the statistical from the data, statistical from the size of the Monte Carlo sample and the systematic uncertainty, respectively. In addition, based on this measurement, we give an updated value for the CKM matrix element $|V_{cb}|$.