V cb determination from inclusive b → c decays: an alternative method

The determination of Vcb relies on the Heavy-Quark Expansion and the extraction of the non-perturbative matrix elements from inclusive b → c decays. The proliferation of these matrix elements complicates their extraction at 1/mb4 and higher, thereby limiting the Vcb extraction. Reparametrization invariance links different operators in the Heavy-Quark expansion thus reducing the number of independent operators at 1/mb4 to eight for the total rate. We show that this reduction also holds for spectral moments as long as they are defined by reparametrization invariant weight-functions. This is valid in particular for the leptonic invariant mass spectrum (q2), i.e. the differential rate and its moments. Currently, Vcb is determined by fitting the energy and hadronic mass moments, which do not manifest this parameter reduction and depend on the full set of 13 matrix elements up to 1/mb4. In light of this, we propose an experimental analysis of the q2 moments to open the possibility of a model-independent Vcb extraction from semileptonic decays including the 1/mb4 terms in a fully data-driven way.