Observation of the $B^0_s\!\to D^{*+}D^{*-}$ decay

TL;DR

This paper reports the first observation of the decay $B^0_s o D^{*+}D^{*-}$, measuring its branching ratio relative to $B^0 o D^{*+}D^{*-}$ using data from the LHCb experiment, with high statistical significance.

Contribution

The paper provides the first observation and precise measurement of the $B^0_s o D^{*+}D^{*-}$ decay branching ratio, including detailed uncertainties and correction factors.

Findings

Decay observed with more than 10 standard deviations

Branching ratio relative to $B^0$ decay measured as 0.269 ± 0.032 ± 0.011 ± 0.008

Absolute branching fraction calculated as (2.15 ± 0.26 ± 0.09 ± 0.06 ± 0.16)×10^{-4}

Abstract

The first observation of the $B^0_s\!\to D^{*+}D^{*-}$ decay and the measurement of its branching ratio relative to the $B^0\!\to D^{*+}D^{*-}$ 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 $B^0_s\!\to D^{*+}D^{*-}$ 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 $B^0\!\to D^{*+}D^{*-}$branching fraction. These results are calculated using the average $B^0_s$ meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light $B^0_s$ eigenstate is considered.