Evidence for the suppressed decay B- -?? DK-, D -?? K+ pi(-)pi(0)

We report a study of the suppressed decay B- -> DK-, D -> K+ pi(-) pi(0), where D denotes either a D-0 or a (D) over bar (0) meson. The decay is sensitive to the CP-violating parameter phi(3). Using a data sample of 772 x 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the Belle detector, we measure the ratio of branching fractions of the above suppressed decay to the favored decay B- -> DK-, D -> K- pi(+) pi(0). Our result is R-DK = [1.98 +/- 0.62 (stat) +/- 0.24 (syst)] x 10(-2), which indicates the first evidence of the signal for this suppressed decay with a significance of 3.2 standard deviations. We measure the direct CP asymmetry between the suppressed B- and B+ decays to be A(DK) = 0.41 +/- 0.30(stat) +/- 0.05(syst). We also report measurements for the analogous quantities R-D pi and A(D pi) for the decay B- -> D pi(-), D -> K+ pi(-)pi(0).We thank the KEKB group for the excellent operation of the accelerator; the KEK cryogenics group for the efficient operation of the solenoid; and the KEK computer group, the National Institute of Informatics, and the PNNL/EMSL computing group for valuable computing and SINET4 network support. We acknowledge support from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS), and the Tau-Lepton Physics Research Center of Nagoya University; the Australian Research Council and the Australian Department of Industry, Innovation, Science and Research; Austrian Science Fund under Grant No. P 22742- N16; the National Natural Science Foundation of China under Contracts No. 10575109, No. 10775142, No. 10825524, No. 10875115, No. 10935008, and No. 11175187; the Ministry of Education, Youth and Sports of the Czech Republic under Contract No. MSM0021620859; the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft and the Volkswagen Stiftung; the Department of Science and Technology of India; the Istituto Nazionale di Fisica Nucleare of Italy; the WCU program of the Ministry Education Science and Technology, National Research Foundation of Korea Grants No. 2011-0029457, No. 2012-0008143, No. 2012R1A1A2008330, and No. 2013R1A1A3007772, BRL program under NRF Grant No. KRF-2011-0020333, BK21 Plus program, and GSDC of the Korea Institute of Science and Technology Information; the Polish Ministry of Science and Higher Education and the National Science Center; the Ministry of Education and Science of the Russian Federation and the Russian Federal Agency for Atomic Energy; the Slovenian Research Agency; the Basque Foundation for Science (IKERBASQUE) and the UPV/EHU under program UFI 11/55; the Swiss National Science Foundation; the National Science Council and the Ministry of Education of Taiwan; and the U.S. Department of Energy and the National Science Foundation. This work is supported by a Grant-in-Aid from MEXT for Science Research in a Priority Area ("New Development of Flavor Physics'') and from JSPS for Creative Scientific Research ("Evolution of Tau-lepton Physics'')