Impact of background effects on the inclusive V cb determination

Abstract

Abstract The determination of the CKM element V cb from inclusive semileptonic b → cℓ ν ¯ $$ \overline{\nu} $$ decays has reached a high precision thanks to a combination of theoretical and experimental efforts. Aiming towards even higher precision, we discuss two processes that contaminate the inclusive V cb determination; the b → u background and the contribution of the tauonic mode: b → c(τ → μν ν ¯ $$ \overline{\nu} $$ ) ν ¯ $$ \overline{\nu} $$ . Both of these contributions are dealt with at the experimental side, using Monte-Carlo methods and momentum cuts. However, these contributions can be calculated with high precision within the Heavy-Quark Expansion. In this note, we calculate the theoretical predictions for these two processes. We compare our b → u results qualitatively with generator-level Monte-Carlo data used at Belle and Belle II. Finally, we suggest to change the strategy for the extraction of V cb by comparing the data on B → Xℓ directly with the theoretical expressions, to which our paper facilitates.

Keywords

• QCD Phenomenology