Observation of the $B^0\to {\rho }^0{\rho }^0$ decay from an amplitude analysis of $B^0\to ({\pi }^{+}{\pi }^{-})({\pi }^{+}{\pi }^{-})$ decays

Abstract

Proton-proton collision data recorded in 2011 and 2012 by the \lhcb experiment, co\-rres\-pon\-ding to an integrated luminosity of 3.0\invfb, are a\-na\-lysed to search for the charmless $B^0\to {\rho }^0{\rho }^0$ decay. More than 600 ${\B^0 \to (π^+π^-)(π^+π^-)}$ signal decays are selected and used to perform an amplitude analysis from which the $B^0\to {\rho }^0{\rho }^0$ decay is observed for the first time with 7.1 standard deviations significance. The fraction of $B^0\to {\rho }^0{\rho }^0$ decays yielding a longitudinally polarised final state is measured to be $\fL = 0.745^{+0.048}_{-0.058} ({\rm stat}) \pm 0.034 ({\rm syst})$. The $B^0\to {\rho }^0{\rho }^0$ branching fraction, using the ${\B^0 \to ϕK^*(892)^{0}}$ decay as reference, is also reported as ${\BF(B^0 \to ρ^0 ρ^0) = (0.94 \pm 0.17 ({\rm stat}) \pm 0.09 ({\rm syst}) \pm 0.06 ({\rm BF})) \times 10^{-6}}$.

as published in PLB

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