First observation of the decay B-s(0) -> K*(0)(K)over-bar*(0)

The first observation of the decay B-s(0) -> K*(0)(K) over bar*(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+pi(-))(K-pi(+)) events are observed within +/- 50 MeV/c(2) of the B-s(0) mass and 746 MeV/c(2) < m(K pi) < 1046 MeV/c(2), mostly coming from a resonant B-s(0) -> K*(0)(K) over bar*(0) signal. The branching fraction and the CP-averaged K*(0) longitudinal polarization fraction are measured to B(B-s(0) -> K*(0)(K) over bar*(0)) = (2.81 +/- 0.46(stat.) +/- 0.45(syst.) +/- 0.34(f(s)/f(d))) x 10(-5) and f(L) = 0.31 +/- 0.12(stat.) +/- 0.04(syst.). (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.