## An effective theory approach to NP in $b \to u$ and $b \to c$ leptonic and semileptonic decays    [PDF]

Rupak Dutta, Anupama Bhol, Anjan K Giri
Recent measurements of exclusive $B^{-} \to \tau^{-}\,\nu$ and $B^0 \to \pi^{+}\,l^{-}\,\bar{\nu}_l$ decays via $b \to u\,l\,\nu$ transition process differ from the Standard Model expectation and if persist in future $B$ experiments, will be definite hint of the Physics beyond the Standard Model. Similar hints of New Physics have been observed in $b \to c$ semileptonic transition processes as well. BaBar measures the ratio of branching fractions of $B \to (D,\,D^{\ast})\,\tau\,\nu$ to the corresponding $B \to (D,\,D^{\ast})\,l\nu$, where $l$ represents either an electron or a muon, and finds $3.4\sigma$ discrepancy with the SM expectation. In this context, we consider a most general effective Lagrangian for the $b \to u\,l\,\nu$ and $b \to c\,l\,\nu$ transition processes in the presence of New Physics and perform a combined analysis of all the $b \to u$ and $b \to c$ semi-(leptonic) data to explore various New Physics operators and their couplings. We consider various New Physics scenarios and give prediction for the $B_c \to \tau\nu$ and $B \to \pi\tau\nu$ decay branching fractions. We also study the effect of these New Physics parameters on the ratio of the branching ratios of $B \to \pi\tau\nu$ to the corresponding $B \to \pi\,l\,\nu$ decays.
View original: http://arxiv.org/abs/1307.6653