Time-dependent Dalitz Plot Analysis of B0 --> Ks pi+ pi-

Abstract

We perform a time-dependent Dalitz plot analysis of $B^0\to K_S^0{\pi }^{+}{\pi }^{-}$ in order to extract the $CP$ violation parameters of $f_0(980)K_S^0$ and ${\rho }^0(770)K_S^0$ and direct $CP$-asymmetries of $K^{\ast +}(892){\pi }^{-}$. The results are obtained from a data sample of $(383\pm 3)\times 10^6$ $B\bar{B}$ decays, collected with the BaBar detector at the PEP2 asymmetric--energy $B$ factory at SLAC. The measured values of $2{\beta }_{\mathrm{eff}}$ in $B^0$ decays to $f_0(980)K_S^0$ and ${\rho }^0(770)K_S^0$ are $(89_{-20}^{+22}\pm 5\pm 8{)}^{\circ }$ and $(37_{-17}^{+19}\pm 5\pm 6{)}^{\circ }$, respectively, where the first quoted uncertainty is statistical, the second is systematic and the third is Dalitz plot signal model uncertainty. We measure the significance of $2{\beta }_{\mathrm{eff}}(f_0(980)K_S^0)\ne 0$ to be $4.3\sigma$. In decays to $K^{\ast }(892)\pi$ we find $A_{CP}=-0.18\pm 0.10\pm 0.03\pm 0.03$. The measured phase difference between the decay amplitudes of $B^0\to K^{\ast +}(892){\pi }^{-}$ and ${\bar{B}}^0\to K^{\ast -}(892){\pi }^{+}$ is $(-164\pm 24\pm 12\pm 15{)}^{\circ }$. All results are preliminary.

29 pages, 19 postscript figures, submitted to Lepton-Photon 2007