Observation of B0 -> K*0 K*0bar and search for B0 -> K*0 K*0

TL;DR

This paper reports the first observation of the B0 -> K*0 K*0bar decay, measuring its branching fraction and polarization, and sets an upper limit on the related decay B0 -> K*0 K*0.

Contribution

First observation of the B0 -> K*0 K*0bar decay with measured branching fraction and polarization, advancing understanding of b -> d penguin processes.

Findings

Branching fraction for B0 -> K*0 K*0bar is approximately 1.28 x 10^{-6}.

Longitudinal polarization fraction is about 0.80.

Upper limit for B0 -> K*0 K*0 decay is set at 0.41 x 10^{-6}.

Abstract

We report the observation of the b -> d penguin-dominated decay B0 -> K*0 K*0bar with a sample of 383.2 +/- 4.2 million BBbar pairs collected with the BaBar detector at the PEP-II asymmetric-energy e^+e^- collider at the Stanford Linear Accelerator Center. The measured branching fraction is Br(B0 -> K*0 K*0bar) = [1.28^{+0.35}_{-0.30} +/- 0.11] x 10^{-6} and the fraction of longitudinal polarization f_L (B0 -> K*0 K*0bar) = 0.80^{+0.10}_{-0.12} +/- 0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for Br(B0 ->K*0 K*0) < 0.41 x 10^{-6}.