# The $V_{cb}$ puzzle: an update

## TL;DR

This paper updates the determination of the CKM element |V_{cb}| using recent Belle data, compares it with inclusive decay results, and provides Standard Model predictions for related observables, highlighting ongoing discrepancies and future prospects.

## Contribution

It offers an updated |V_{cb}| value based on new experimental analysis and discusses its implications for the $b o c au
u$ observables, emphasizing the importance of lattice form factor calculations.

## Key findings

- |V_{cb}| is about 2σ from inclusive decay determinations.
- The |V_{cb}| value is highly sensitive to the form factor slope at zero recoil.
- Predictions for $R(D^*)$, $P_ au$, and $F_L^{D^*}$ are provided within the Standard Model.

## Abstract

We discuss the impact of the recent untagged analysis of ${B}^0\rightarrow D^{*}l\bar{\nu}_l$ decays by the Belle Collaboration on the extraction of the CKM element $|V_{cb}|$ and provide updated SM predictions for the $b\to c\tau\nu$ observables $R(D^*)$, $P_\tau$, and $F_L^{D^*}$. The value of $|V_{cb}|$ that we find is about $2\sigma$ from the one from inclusive semileptonic $B$ decays, and is very sensitive to the slope of the form factor at zero recoil which should soon become available from lattice calculations.