LHCb CollaborationAdeva Andany, BernardoBaladrón Rodríguez, PabloBoente García, ÓscarBrea Rodríguez, AlexandreCasais Vidal, AdriánChobanova, VeronikaCid Vidal, XabierDalseno, JeremyDieste Maroñas, LorenaFernández Prieto, AntonioGallas Torreira, Abraham AntonioGarcía Plana, BeatrizGioventù, AlessandraLomba Castro, JuliánMartínez Santos, DiegoParkinson, Chris J.Plo Casasus, MáximoProuve, ClaireRomero Lamas, MarcosRomero Vidal, AntonioSaborido Silva, Juan JoséSantamarina Ríos, CibránSellam, SaraVázquez Gómez, R.Vázquez Regueiro, Pablo2021-08-042021-08-042021The LHCb collaboration., Aaij, R., Abellán Beteta, C. et al. Angular analysis of B0→D∗−D∗+s with D∗+s→D+sγ decays. J. High Energ. Phys. 2021, 177 (2021). https://doi.org/10.1007/JHEP06(2021)177http://hdl.handle.net/10347/26693The first full angular analysis of the B0→D∗−D∗+s decay is performed using 6 fb−1 of pp collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The D∗+s→D+sγ and D*− → D¯¯¯¯0π− vector meson decays are used with the subsequent D+s → K+K−π+ and D¯¯¯¯0 → K+π− decays. All helicity amplitudes and phases are measured, and the longitudinal polarisation fraction is determined to be fL = 0.578 ± 0.010 ± 0.011 with world-best precision, where the first uncertainty is statistical and the second is systematic. The pattern of helicity amplitude magnitudes is found to align with expectations from quark-helicity conservation in B decays. The ratio of branching fractions [ℬ(B0→D∗−D∗+s) × ℬ(D∗+s→D+sγ)]/ℬ(B0 → D*−D+s) is measured to be 2.045 ± 0.022 ± 0.071 with world-best precision. In addition, the first observation of the Cabibbo-suppressed Bs → D*−D+s decay is made with a significance of seven standard deviations. The branching fraction ratio ℬ(Bs → D*−D+s)/ℬ(B0 → D*−D+s) is measured to be 0.049 ± 0.006 ± 0.003 ± 0.002, where the third uncertainty is due to limited knowledge of the ratio of fragmentation fractionsengCopyright CERN, for the benefit of the LHCb Collaboration 2021. Open Access . This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are creditedAtribución 4.0 Internacionalhttp://creativecommons.org/licenses/by/4.0/B physicsBranching fractionHadron-Hadron scattering (experiments)Polarizationjournal article10.1007/JHEP06(2021)177open access