| Abstract |
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We search for the decays B0->rho0rho0, B0->rho0f0, and B0->f0f0
in a sample of about 384 million Upsilon(4S)->BBbar decays collected
with the BABAR detector at the PEP-II asymmetric-energy e+e- collider
at SLAC. We find evidence for B0->rho0rho0 with 3.5 sigma significance
and measure the branching fraction BR = (1.07+-0.33+-0.19)10^-6
and longitudinal polarization fraction f_L = 0.87+-0.13+-0.04, where
the first uncertainty is statistical, and the second is systematic.
The uncertainty on the CKM unitarity angle alpha due to penguin
contributions in B-> rho rho decays is 18 degrees at the 1 sigma level.
We also set upper limits on the B0->rho0f0 and B0->f0f0 decay rates.
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