CP-violating polarizations in semileptonic heavy meson decays

Abstract

We study the T -violating lepton transverse polarization (P ⊥ 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 → sγ) and CP violating processes, we find that in B decays, P ⊥ of the muon in multi-Higgs doublet models can be of order 10%, while P ⊥ of the τ can even approach unity. In contrast, P ⊥ µ in D decays is at most 1.5%. We discuss possibilities for detection of P ⊥ l at current and future B factories. We also show that P ⊥ l in decays to vector mesons, unlike in decays to pseudoscalars, can get contributions from left-right models. Unfortunately, P ⊥ l in that case is proportional to W L -W R mixing, and is thus small.

Polarization measurements andTviolation in exclusive semileptonicBdecays

“…which is in agreement with a previous estimate [18]. Qualitatively similar results have been found in the inclusive case [17,19].…”

“…This observable is thus complementary to its analogue in the decay B → Dτ ν, which is sensitive to effective scalar interactions. We note in passing that Garisto [18] has found the transverse tau polarization in B → D * τ ν to have an additional dependence on effective right-handed quark-current interactions. There is no discrepancy with our results, however, since the effect which Garisto discusses only arises when one fixes the polarization state of the D * , instead of summing over polarizations as we have done.…”

“…One can define analogous quantities for the leptons in the decays B→D ( * ) ℓν and one finds that, neglecting tensor effects, they are sensitive to non-SM scalar and pseudoscalar effective interactions in the D and D * cases, respectively [3]. The τ lepton polarization in these decays has been studied in multi-Higgs models [17][18][19][20] and, more recently, in R-parity conserving supersymmetric (SUSY) models with large intergenerational squark mixing [12,3]. In the latter case the effect arises at one loop.…”

Tau longitudinal polarization inB¯→Dτν¯and its role in the search for the charged Higgs boson

“…It is possible to define two distinct and independent τ polarizations, namely the transverse polarization and the longitudinal one. The transverse polarization is known to be generated by T violating interactions and/or final state interactions [11][12][13]. Both interactions are small in the SM.…”

“…20 that the distribution of the angle between the momenta of the D meson and the pion in τ → πν in the B rest frame depends on the magnitude and the complex phase of the charged Higgs coupling. It is also expected that the information on τ polarizations, which are affected by the charged Higgs boson [9,[11][12][13], is encoded in the decay distribution of successive τ decays.…”