Improved Measurements of CP-Violating Asymmetries in B0 --> pi+pi- Decays

Abstract

We present preliminary updated measurements of the CP-violating parameters $S_{\pi\pi}$ and $C_{\pi\pi}$ in $B^0\to\pi^+\pi^-$ decays. Using a sample of 227 million $\Upsilon(4S)\to B\bar{B}$ decays collected with the BaBar detector at the PEP-II asymmetric-energy $e^+e^-$ collider at SLAC, we observe $467\pm 33$ signal decays and measure $S_{\pi\pi}$ and $C_{\pi\pi} = -0.30\pm 0.17 ({\rm stat})\pm 0.03 ({\rm syst})$, and $C_{\pi\pi} = -0.09\pm 0.15 ({\rm stat})\pm 0.04 ({\rm syst})$.