Observation of the B0s → D∗+D∗− decay

The first observation of the → D∗+D∗− decay and the measurement of its branching ratio relative to the B0 → D∗+D∗− decay are presented. The data sample used corresponds to an integrated luminosity of 9 fb−1 of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018. The decay is observed with more than 10 standard deviations and the time-integrated ratio of branching fractions is determined to be where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio fs/fd. The → D*+D*− branching fraction is calculated to be where the fourth uncertainty is due to the B0 → D*+D*− branching fraction. These results are calculated using the average meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light eigenstate is considered.