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

TL;DR

This paper measures the form factors in B0 to D* e nu decay using a large data sample, providing precise parameter values and an updated CKM matrix element |Vcb|, advancing understanding of semileptonic B decays.

Contribution

It presents the first detailed measurement of the three form factors in B0 to D* e nu decay using angular and momentum transfer dependence, with improved precision.

Findings

Measured form factor ratios R1 and R2 with high precision.

Determined the parameter ρ² describing the momentum dependence of A₁.

Provided an updated value for |Vcb| based on the measurements.

Abstract

We measure the dependence of $\bar B^0 \to D^{*+}e^-\bar{\nu}_e$ on the decay angles and momentum transfer. The data sample consists of $\sim 86 \times 10^6$ $B\bar B$-pairs accumulated on the $\Upsilon(4{\rm S})$ 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 $\rho^2$ 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 $\rho^2$ 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 $\rho^2=1.145\pm 0.059\pm 0.030\pm 0.035$. 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 $|V_{cb}|$.