Observation of the B0 →ρ0ρ0 decay from an amplitude analysis of B0 → (π+π-) (π+π-) decays

Abstract

Proton-proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb−1 , are analysed to search for the charmless B0 → ρ 0ρ 0 decay. More than 600 B0 → (π +π −)(π +π −) signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0 → ρ 0ρ 0 decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0 → ρ 0ρ 0 decays yielding a longitudinally polarised final state is measured to be fL = 0.745+0.048 −0.058(stat) ± 0.034(syst). The B0 → ρ 0ρ 0 branching fraction, using the B0 → φK∗ (892)0 decay as reference, is also reported as B(B0 → ρ 0ρ 0 ) = (0.94 ± 0.17(stat) ± 0.09(syst) ± 0.06(BF)) × 10−6 .