Observation of the B[superscript 0] → p[superscript 0]p[superscript 0] decay from an amplitude analysis of B[superscript 0] → (π[superscript +]π[superscript −])(π[superscript +]π[superscript −]) decays

Abstract

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