Evidence for B+ -> K*0bar K*+

We present measurements of the branching fraction and fraction of longitudinal polarization for the decay B+ -> K0bar K+ with a sample of 467 +/- 5 million BBbar pairs collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at the SLAC National Accelerator Laboratory. We obtain the branching fraction Br(B+ -> K0bar K+) = (1.2 +/- 0.5 +/- 0.1) x 10^{-6} with a significance of 3.7 standard deviations including systematic uncertainties. We measure the fraction of longitudinal polarization f_L = 0.75+0.16-0.26 +/- 0.03. The first error quoted is statistical and the second is systematic.