Revisiting fits to $B^{0} \to D^{*-} \ell^{+} \nu_{\ell}$ to measure $|V_{cb}|$ with novel methods and preliminary LQCD data at non-zero recoil

TL;DR

This paper refines the measurement of the CKM matrix element |V_{cb}| from B0 to D* l nu decays using novel statistical techniques, multiple form factor parametrizations, and preliminary lattice QCD data to reduce model dependence.

Contribution

It introduces a new method employing toy MC with Cholesky decomposition to mitigate systematic errors and incorporates preliminary lattice QCD data for more model-independent |V_{cb}| extraction.

Findings

Consistent results across different fit configurations.

Reduced model dependence with lattice QCD inputs.

Approximate value of (1)ta_{EW}|V_{cb}| around 35 imes 10^{-3}.

Abstract

We present a study of fits to exclusive $B^{0} \to D^{*-} \ell^{+} \nu_{\ell}$ measurements for the determination of the Cabbibo-Kobayashi-Maskawa matrix element magnitude $|V_{cb}|$, based on the most recent Belle untagged measurement. Results are obtained with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parametrizations, with and without the inclusion of preliminary Lattice QCD measurements of form factors at non-zero hadronic recoil from the JLQCD collaboration. The CLN and BGL fits are also studied in different scenarios with reduced theoretical assumptions, and at higher order expansions, respectively. To avoid bias from high systematic error correlations we employ a novel technique in the field of $B$-physics phenomenology with a toy MC using a Cholesky decomposition of the covariance matrix. Using additional input from Lattice QCD calculations of form factors at non-zero recoil, in collaboration with JLQCD, allows for well-defined fit results with reduced model dependence in CLN and BGL. The results obtained are consistent between different configurations, ultimately providing a method for a more model-independent exclusive measurement of $|V_{cb}|$. Using preliminary inputs, $\mathcal{F}(1)\eta_{\rm EW}|V_{cb}|$ is found to be approximately $(35.02 \pm 0.29 \pm 0.88) \times 10^{-3}$ in BGL(2,2,2) and $(34.96 \pm 0.32 \pm 0.96) \times 10^{-3}$ in CLNnoHQS.