First observation of the decay Bs0→K*0K̄*0

Abstract The first observation of the decay B s 0 → K ⁎ 0 K ¯ ⁎ 0 is reported using 35 pb − 1 of data collected by LHCb in proton–proton collisions at a centre-of-mass energy of 7 TeV. A total of 49.8 ± 7.5 B s 0 → ( K + π − ) ( K − π + ) events are observed within ± 50 MeV / c 2 of the B s 0 mass and 746 MeV / c 2 m K π 1046 MeV / c 2 , mostly coming from a resonant B s 0 → K ⁎ 0 K ¯ ⁎ 0 signal. The branching fraction and the CP -averaged K ⁎ 0 longitudinal polarization fraction are measured to be B ( B s 0 → K ⁎ 0 K ¯ ⁎ 0 ) = ( 2.81 ± 0.46 ( stat. ) ± 0.45 ( syst. ) ± 0.34 ( f s / f d ) ) × 10 − 5 and f L = 0.31 ± 0.12 ( stat. ) ± 0.04 ( syst. ) .