https://doi.org/10.1140/epjc/s10052-017-5272-0
Regular Article - Theoretical Physics
Lepton polarization asymmetries in rare semi-tauonic 
exclusive decays at FCC-ee
1
Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
2
Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000, Ljubljana, Slovenia
3
Université Clermont Auvergne, CNRS/IN2P3, LPC, 63000, Clermont-Ferrand, France
4
Taras Shevchenko National University of Kyiv, 01601, Kyiv, Ukraine
* e-mail: luiz.vale@th.u-psud.fr
Received:
8
August
2017
Accepted:
1
October
2017
Published online:
24
October
2017
We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the 
transition, at a future high-energy circular electron–positron collider (FCC-ee). We argue that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic 
decay modes (up to discrete ambiguities). This, together with the potentially large statistics of 
, opens the door for the experimental determination of polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the polarizations and suggest suitable theoretically clean observables in the form of single- and double- polarization asymmetries.
© The Author(s), 2017
