Speaker
Description
Recently Belle, BaBar, and LHCb reported on a large deviation of $R(D^{(*)})$ from the Standard Model (SM) prediction. In many theoretical attempts to explain this disagreement the new interactions, that can be of different Lorentz structure from $V-A$, are implemented. If the amplitude of the new interaction is proportional to the lepton mass, we can expect that $e$-$\mu$ lepton nonuniversality will be also revealed in semileptonic $B$-decays. In particular, one can expect the difference of $D^{*+}$ polarizations in $\bar B \to D^{*+} l^{-} \bar \nu_{l}$ ($l$ denotes $e$ or $\mu$) due to small non $V-A$ correction to the semimuonic decay. We choose the $D^{*+}$ polarization as a probe for new contribution because the systematic effects of different $\mu$ and $e$ reconstruction and identification efficiencies are cancelled out in each bin of the lepton momentum.
We perform the Monte Carlo study to verify the method of $\bar B \to D^{*+} l^{-} \bar\nu_{l}$ reconstruction and optimization of the selection criteria for the highest statistical and systematic accuracy. We studied all possible backgrounds and divided them into three categories: those, obtained from the data, universal backgrounds, i.e. real leptons which contribute equally to both electron and muon samples, and flavor dependent, which can contribute differently. The latter causes the most systematic errors to the proposed measurement. Using the Belle sample of generic Monte Carlo for both charged and neutral $B$-meson production, we studied how to decrease and then estimate the systematic uncertainty of the measurement.
