Branching Fractions and CP-Violating Asymmetries in Radiative B Decays to eta K gamma

We present measurements of the CP-violation parameters S and C for the radiative decay B0 -> eta K0s gamma; for B -> eta K gamma we also measure the branching fractions and for B+ -> eta K+ gamma the time-integrated charge asymmetry Ach. The data, collected with the BaBar detector at the Stanford Linear Accelerator Center, represent $465\times {10}^6$ BBbar pairs produced in $e^{+}{e}^{-}$ annihilation. The results are $S = -0.18^{+0.49}{-0.46} \pm 0.12$,$C = -0.32^{+0.40}{-0.39} \pm 0.07$,BF(B0->etaK0gamma)=$(7.1^{+2.1}{-2.0} \pm 0.4) \times 10^{-6}$,BF(B+->etaK+gamma)=$(7.7±1.0 \pm 0.4) \times 10^{-6}$,andAch=$(-9.0^{+10.4}{-9.8} \pm 1.4) \times 10^{-2}$. The first error quoted is statistical and the second systematic.