Transverse Spin Polarization of $\tau^-$ in ${\bar{B}}^0\rightarrow D^{+} \tau^- {\bar{\nu}}$ and Charged Higgs Boson

TL;DR

This paper investigates the potential transverse polarization of the tau lepton in B meson decays as a probe for the existence of charged Higgs bosons with complex couplings, using measured form factors.

Contribution

It introduces a method to calculate tau transverse polarization in B decays considering charged Higgs contributions with complex phases, linking it to new physics detection.

Findings

Transverse tau polarization can be non-zero if charged Higgs exists with complex couplings.

The polarization depends on the phase of the charged Higgs coupling.

Results suggest polarization measurements could indicate new physics beyond the Standard Model.

Abstract

The spin of the $\tau$ lepton in the semiletonic process ${\bar{B}}^0\rightarrow D^{+} \tau^- {\bar{\nu}}$ can be polarized in the direction which is normal to the reaction plane, if the charged Higgs boson exists and its coupling to quarks has a complex phase. We calculate this transverse polarization of the $\tau$ lepton by using the experimentally measured $B$ to $D$ transition form factors.