Observation of D^+ to eta e^+ nu_e
  Using a 281 pb^-1 data sample collected at the psi(3770) resonance with the CLEO-c detector at the Cornell Electron Storage Ring, we report the first observation of D^+ to eta e^+ nu_e. We also set upper limits for D^+ to eta' e^+ nu_e and D^+ to phi e^+ nu_e that are about two orders of magnitude more restrictive than those obtained by previous experiments. 
CLEO Collaboration: R. E. Mitchell, et al