# Dortmund 2021 – wissenschaftliches Programm

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# T: Fachverband Teilchenphysik

## T 31: Flavour physics II

### T 31.8: Vortrag

### Dienstag, 16. März 2021, 17:45–18:00, Tf

**Towards a new determination of Vcb** — •Kevin Olschewsky^{1}, Keri Vos^{2}, and Matteo Fael^{3} — ^{1}Center for Particle Physics Siegen, Theoretische Physik 1, Universität Siegen — ^{2}Faculty of Science and Engineering, Maastricht University — ^{3}Institute of Theoretical Particle Physics, KIT Karlsruhe

A more precise determination of $V_{cb}$ is an important tool for future tests of the SM. It causes the main uncertainty in parameters of $CP$-violation as well as several flavour-changing neutral current decays. Direct information on $V_{cb}$ can be obtained from inclusive semileptonic B decays, for which the Heavy Quark Expansion (HQE) has become the standard tool in the theoretical description. It allows us to express physical observables in a combined expansion of $\alpha_s$ and $\Lambda_{QCD}/m_b$, where the non-perturbative input comes in form of forward matrix elements of local operators. Their extraction is possible up to order $1/m_b^3$, yet at higher orders their proliferation prevents the extraction from data.

In this talk I will discuss how reparametrization invariance in the HQE reduces the number of independent parameters and how specific observables - in this case total rates and $q^2$-moments (the moments of the leptonic invariant mass spectrum), can be used to extract a value for $V_{cb}$ up to order $1/m_b^4$ without the need to model any HQE parameters. Finally I will outline how this approach will be used to evaluate $q^2$-moments (that are currently being measured!) and lead to a more precise determination of $V_{cb}$ in the future.