The Z boson spin observables as messengers of new physicsJ. A. Aguilar-Saavedra, J. Bernabéu, V. A. Mitsou and A. SegarraEur. Phys. J. C, 77 4 (2017) 234DOI: https://doi.org/10.1140/epjc/s10052-017-4795-8