Effective theory approach to new physics inb→uandb→cleptonic and semileptonic decays

Abstract

Recent measurements of exclusive ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\nu}$ and ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{l}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{l}$ decays via the $b\ensuremath{\rightarrow}ul\ensuremath{\nu}$ transition process differ from the standard model expectation and, if they persist in future $B$ experiments, will be a definite hint of the physics beyond the standard model. Similar hints of new physics have been observed in $b\ensuremath{\rightarrow}c$ semileptonic transition processes as well. BABAR measures the ratio of branching fractions of $B\ensuremath{\rightarrow}(D,{D}^{*})\ensuremath{\tau}\ensuremath{\nu}$ to the corresponding $B\ensuremath{\rightarrow}(D,{D}^{*})l\ensuremath{\nu}$, where $l$ represents either an electron or a muon, and finds $3.4\ensuremath{\sigma}$ discrepancy with the standard model expectation. In this context, we consider a most general effective Lagrangian for the $b\ensuremath{\rightarrow}ul\ensuremath{\nu}$ and $b\ensuremath{\rightarrow}cl\ensuremath{\nu}$ transition processes in the presence of new physics and perform a combined analysis of all the $b\ensuremath{\rightarrow}u$ and $b\ensuremath{\rightarrow}c$ semi-(leptonic) data to explore various new physics operators and their couplings. We consider various new physics scenarios and give predictions for the ${B}_{c}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\nu}$ and $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\tau}\ensuremath{\nu}$ decay branching fractions. We also study the effect of these new physics parameters on the ratio of the branching ratios of $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\tau}\ensuremath{\nu}$ to the corresponding $B\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$ decays.