We present the first observation of the decay B+ -> rho+ K-(0), using a data sample of 348 fb(-1) collected at the Upsilon(4S) resonance with the BABAR detector. The branching fraction and charge asymmetry are measured to be (8.0(-1.3)(+1.4) ± 0.6)x10(-6) and (-12.2 ± 16.6 ± 2.0)%, respectively, where the first uncertainty is statistical and the second is systematic. The charge asymmetry is defined by A(ch)=(Gamma(-)(B)-Gamma(+)(B))/(Gamma(-)(B)+Gamma(+)(B)) with Gamma(±)(B) the B-± decay rate. The significance of the observed branching fraction, including systematic uncertainties, is 7.9 standard deviations.

This work is supported by DOE and NSF (USA), NSERC (Canada), CEA and CNRS-IN2P3 (France), BMBF and DFG (Germany), INFN (Italy), FOM (The Netherlands), NFR (Norway), MIST (Russia), MEC (Spain), and PPARC (United Kingdom). Individuals have received support from the Marie Curie EIF (European Union) and the A. P. Sloan Foundation.

8 pages, 1 figure.-- PACS nrs.: 13.25.Hw; 11.30.Er; 12.15.Hh.-- ISI Article Identifier: 000248544300003.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ex/0702043.-- et al. (BABAR Collaboration).

Peer reviewed