Observation of the Bs0 → D ^*+ D ^*− decay

Abstract

Abstract The first observation of the $$ {B}_s^0 $$ B s 0

→ 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$$ \frac{\mathcal{B}\left({B}_s^0\to {D}^{\ast +}{D}^{\ast -}\right)}{\mathcal{B}\left({B}^0\to {D}^{\ast +}{D}^{\ast -}\right)}=0.269\pm 0.032\pm 0.011\pm 0.008, $$

B

B s 0

→

D

∗ +

D

∗ −

B

B 0

→

D

∗ +

D

∗ −

= 0.269 ± 0.032 ± 0.011 ± 0.008 , where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio fs/fd. The $$ {B}_s^0 $$

B s 0

→ D*+D*− branching fraction is calculated to be$$ \mathcal{B}\left({B}_s^0\to {D}^{\ast +}{D}^{\ast -}\right)=\left(2.15\pm 0.26\pm 0.09\pm 0.06\pm 0.16\right)\times {10}^{-4}, $$ B

B s 0

→

D

∗ +

D

∗ −

=

2.15 ± 0.26 ± 0.09 ± 0.06 ± 0.16

×

10

− 4

, where the fourth uncertainty is due to the B0→ D*+D*− branching fraction. These results are calculated using the average $$ {B}_s^0 $$

B s 0

meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light $$ {B}_s^0 $$

B s 0

eigenstate is considered.