CP violating polarizations in semileptonic heavy meson decays

Abstract

We study the $T$-violating lepton transverse polarization ($P^\perp_l$) in three body semileptonic heavy meson decays to pseudoscalar mesons and to vector mesons. We calculate these polarizations in the heavy quark effective limit, which simplifies the expressions considerably. After examining constraints from $CP$ conserving (including $b \rightarrow s \gamma$) and $CP$ violating processes, we find that in $B$ decays, $P^\perp$ of the muon in multi-Higgs doublet models can be of order $10\%$, while $P^\perp$ of the $\tau$ can even approach unity. In contrast, $P^\perp_\mu$ in $D$ decays is at most 1.5\%. We discuss possibilities for detection of $P^\perp_l$ at current and future $B$ factories. We also show that $P^\perp_l$ in decays to vector mesons, unlike in decays to pseudoscalars, can get contributions from left-right models. Unfortunately, $P^\perp_l$ in that case is proportional to $W_L$-$W_R$ mixing, and is thus small.