Determination of the Form Factors for the Decay B0 -> D*- l+ nu_l and of the CKM Matrix Element |V_cb|

TL;DR

This paper measures the form factors and the CKM matrix element |V_{cb}| for B0 -> D*- l+ nu_l decay using BaBar data, improving precision through combined analysis and lattice calculations.

Contribution

It provides a combined measurement of form factors and |V_{cb}| with improved precision, utilizing a large data sample and multiple fit techniques.

Findings

Measured form factors rho^2, R_1(1), R_2(1) with reduced uncertainties.

Determined |V_{cb}| with improved accuracy using lattice inputs.

Reported the exclusive branching fraction of B0 -> D*- l+ nu_l decay.

Abstract

We present a combined measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_{cb}| and of the parameters rho^2, R_1(1), and R_2(1), which fully characterize the form factors for the B0 -> D*- l+ nu_l decay in the framework of heavy-quark effective theory. The results, based on a selected sample of about 52,800 B0 -> D*- l+ nu_l decays, recorded by the BaBar detector, are rho2=1.157+-0.094+-0.027, R_1(1)=1.327+-0.131+-0.043, R_2(1)=0.859+-0.077+-0.021, and F(1)|V_cb|=(34.7+-0.4+-1.0)x10^-3. The first error is the statistical and the second is the systematic uncertainty. Combining these measurements with the previous BaBar measurement of the form factors, which employs a different fit technique on a partial sample of the data, we improve the statistical precision of the result, rho2=1.191+-0.048+-0.028, R_1(1)=1.429+-0.061+-0.044, R_2(1)=0.827+-0.038+-0.022, and F(1)|V_cb| = (34.4+-0.3+-1.1)x10^-3. Using lattice calculations for the axial form factor $\mathcal{F}(1)$, we extract |V_cb| =(37.4+-0.3+-1.2+1.2-1.4)x10^-3, where the third error is due to the uncertainty in F(1). We also present a measurement of the exclusive branching fraction, B = (4.69+-0.04+-0.34)%.