Observation of the $B_s^0\to D^{\ast +}{D}^{\ast -}$ decay

Abstract

The first observation of the $B_s^0\to D^{\ast +}{D}^{\ast -}$ decay and the measurement of its branching ratio relative to the $B^0\to D^{\ast +}{D}^{\ast -}$ decay are presented. The data sample used corresponds to an integrated luminosity of $9{\text{fb}}^{-1}$ of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and $13\text{TeV}$ 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 \begin{align*} \frac{\mathcal{B}(B^0_s\!\to D^{*+}D^{*-})}{\mathcal{B}(B^0\!\to D^{*+}D^{*-})} = 0.269 \pm 0.032 \pm 0.011 \pm 0.008\, , \end{align*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio $f_s/f_d$. The $B_s^0\to D^{\ast +}{D}^{\ast -}$ branching fraction is calculated to be \begin{align*} \mathcal{B}(B^0_s\!\to D^{*+}D^{*-}) = (2.15 \pm 0.26 \pm 0.09 \pm 0.06 \pm 0.16)\times 10^{-4} \,, \end{align*} where the fourth uncertainty is due to the $B^0\to D^{\ast +}{D}^{\ast -}$branching fraction. These results are calculated using the average $B_s^0$ meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light $B_s^0$ eigenstate is considered.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-023.html (LHCb public pages)