Aachen 2019 – scientific programme
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T: Fachverband Teilchenphysik
T 71: Theorie: Flavorphysik
T 71.4: Talk
Wednesday, March 27, 2019, 16:45–17:00, H11
Vcb from inclusive b → c ℓ ν decays: an alternative method — •Matteo Fael, Thomas Mannel, and Keri Vos — Universität Siegen, Siegen, Germany
The standard method to extract Vcb from inclusive semileptonic B decays relies on the precise calculation of the inclusive rate as well as of spectral moments (i.e. moments of the charged lepton energy and the hadronic mass spectra) performed in the Heavy Quark Expansion (HQE). The HQE allows us to predict physical observables as a series in ΛQCD/mb and to write them in terms of HQE parameters, the non-perturbative inputs that can be determined on the lattice or fitted from data.
Their extraction from data is possible only up to 1/mb3; up to this order there are only four independent parameters. However starting at order 1/mb4, their proliferation prevents their extraction from data.
In this talk I will discuss how reparametrization invariance, a symmetry within the HQE reflecting Lorentz invariance of the underlying QCD, reduces the number of independent HQE parameters. Specific observables, in particular the total rates and the q2 moments (the moments of the leptonic invariant mass spectrum), indeed depend on a smaller set of non-perturbative inputs. I will propose an alternative extraction of Vcb based on the q2-moment measurement that could push the Vcb determination up to order 1/mb4 without making use of models for the HQE parameters, i.e. to have a fully data-driven analysis up to this order