Study of B0→ρ+ρ− decays and constraints on the CKM angle α

Le résumé fourni par la source

We present results from an analysis of ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{+}{\ensuremath{\rho}}^{\ensuremath{-}}$ decays using $(383.6\ifmmode\pm\else\textpm\fi{}4.2)\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected by the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC. The measurements of the ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{+}{\ensuremath{\rho}}^{\ensuremath{-}}$ branching fraction, longitudinal polarization fraction ${f}_{L}$, and the $CP$-violating parameters ${S}_{\mathrm{long}}$ and ${C}_{\mathrm{long}}$ are as follows: $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{+}{\ensuremath{\rho}}^{\ensuremath{-}})=(25.5\ifmmode\pm\else\textpm\fi{}2.1(\mathrm{stat}{)}_{\ensuremath{-}3.9}^{+3.6}(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, ${f}_{L}=0.992\ifmmode\pm\else\textpm\fi{}0.024(\mathrm{stat}{)}_{\ensuremath{-}0.013}^{+0.026}(\mathrm{syst})$, ${S}_{\mathrm{long}}=\ensuremath{-}0.17\ifmmode\pm\else\textpm\fi{}0.20(\mathrm{stat}{)}_{\ensuremath{-}0.06}^{+0.05}(\mathrm{syst})$, ${C}_{\mathrm{long}}=0.01\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{syst})$. We determine the unitarity triangle angle $\ensuremath{\alpha}$, using an isospin analysis of $B\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\rho}$ decays. One of the two solutions, $\ensuremath{\alpha}=[73.1,117.0]\ifmmode^\circ\else\textdegree\fi{}$ at 68% confidence level, is compatible with standard model-based fits of existing data. Constraints on the unitarity triangle are also evaluated using an $SU(3)$ symmetry-based approach.

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