Measurement of $B^0\toπ^+π^-π^+π^-$ Decays and Search for $B^0\toρ^0ρ^0$

Abstract

We report on a search for the decay $B^0\toρ^0ρ^0$ and other charmless modes with a $π^+π^-π^+π^-$ final state, including $B^0\toρ^0π^+π^-$, non-resonant $B^0\to 4π^{\pm}$, $B^0\toρ^0f_0(980)$, $B^0\to f_0(980)f_0(980)$ and $B^0\to f_0(980)π^+π^-$. These results are obtained from a data sample containing 657 million $B \overline B$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set an upper limit on $\mathcal{B}(B^0\toρ^0ρ^0)$ of $1.0\times 10^{-6}$ at the 90% confidence level (C.L.). From our $B^0\toρ^0ρ^0$ measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase $ϕ_2$ to be $91.7 \pm 14.9$ degrees. We find excesses in $B^0\to ρ^0π^+π^-$ and non-resonant $B^0\to 4π^{\pm}$ with 1.3$σ$ and 2.5$σ$ significance, respectively. The corresponding branching fractions are less than $12.0 \times 10^{-6}$ and $19.3 \times 10^{-6}$ at the 90% C.L. In addition, we set 90% C.L. upper limits as follows: $\mathcal{B}(B^0\toρ^0f_0(980))< 0.3 \times 10^{-6}$, $\mathcal{B}(B^0\to f_0(980)f_0(980))< 0.1 \times 10^{-6}$, and $\mathcal{B}(B^0\to f_0(980)π^+π^-)< 3.8 \times 10^{-6}$.

6 pages, 2 figures. Submitted to PRD(RC)