Observation of B→η′K* and evidence for B+→η′ρ+

We present an observation of B -> eta'K*. The data sample corresponds to 232 x 10(6) BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy B factory at the Stanford Linear Accelerator Center. We measure the branching fractions (in units of 10(-6)) B(B-0 -> eta'K-*0) = 3.8 +/- 1.1 +/- 0.5 and B(B+ -> eta'K*+) = 4.9(-1.7)(+1.9) +/- 0.8, where the first error is statistical and the second systematic. A simultaneous fit results in the observation of B -> eta'K-* with B(B -> eta'K-*) = 4.1(-0.9)(+1.0) +/- 0.5. We also search for B -> eta'rho and eta'f(0)(980)(f(0) -> pi(+) pi(-)) with results and 90% confidence level upper limits B(B+ -> eta'rho(+)) = 8.7(-2.8-1.3)(+3.1+2.3) ( eta'rho(0)) eta'f(0)(980)(f(0) -> pi(+) pi(-))) < 1.5. Charge asymmetries in the channels with significant yields are consistent with zero.