Time-Dependent Analysis of the Decay B0 --> rho0 rho0

Abstract

We study the decay B0 --> rho0 rho0 in a sample of about 427 million Upsilon(4S) --> BBbar decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC. We find the branching fraction B = (0.84 +/- 0.29 +/- 0.17)*1e-6 and longitudinal polarization fraction of f_L = 0.70 +/- 0.14 +/- 0.05, where the first uncertainty is statistical, and the second is systematic. The evidence for the B0 --> rho0 rho0 signal has 3.6 sigma significance. We investigate the proper-time dependence of the longitudinal component in the decay and measure the CP-violating coefficients S^{00}_L = 0.5 +/- 0.9 +/- 0.2 and C^{00}_L = 0.4 +/- 0.9 +/- 0.2, corresponding to the sine and cosine terms in the time evolution of asymmetry. We study the implication of these results for penguin contributions in B --> rho rho decays and for the CKM unitarity angle alpha.