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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2009, vol. 103, p. -

Measurement of the differential branching fraction and forward-backward asymmetry for b→K(*)l+l-

Wei J. T., Chang P., Adachi I., Aihara H., Aulchenko V., Aushev T., Bakich A. M., Balagura V., Barberio E., Bondar A., Bozek A., Bračko M., Browder T. E., Chang Y. W., Chao Y., Chen A., Chen K. F., Cheon B. G., Chiang C. C., Cho I. S., Choi Y., Dalseno J., Drutskoy A., Dungel W., Eidelman S., Gabyshev N., Goldenzweig P., Golob B., Ha H., Han B. Y., Hayasaka K., Hayashii H., Hazumi M., Horii Y., Hoshi Y., Hou W. S., Hyun H. J., Iijima T., Inami K., Itoh R., Iwasaki M., Iwasaki Y., Kah D. H., Kaji H., Kang J. H., Kapusta P., Katayama N., Kawasaki T., Kichimi H., Kim H. J., Kim H. O., Kim S. K., Kim Y. I., Kim Y. J., Kinoshita K., Ko B. R., Korpar S., Križan P., Krokovny P., Kuzmin A., Kwon Y. J., Kyeong S. H., Lange J. S., Lee M. J., Lee S. E., Lesiak T., Li J., Limosani A., Liu C., Liventsev D., Louvot R., Mandl F., Matyja A., McOnie S., Medvedeva T., Miyabayashi K., Miyata H., Miyazaki Y., Mizuk R., Nakano E., Nakao M., Nakazawa H., Natkaniec Z., Nishida S., Nishimura K., Nitoh O., Nozaki T., Ogawa S., Ohshima T.

We study B→K(*)ℓ+ℓ- decays (ℓ=e, μ) based on a data sample of 657×106 BB̄ pairs collected with the Belle detector at the KEKB e+e- collider. We report the differential branching fraction, isospin asymmetry, K* polarization, and the forward-backward asymmetry (AFB) as functions of q2=Mℓ2c2. The fitted AFB spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B→K*ℓ+ℓ-)=(10.7-1.0+1.1±0.9)×10-7 and B(B→Kℓ+ℓ-)=(4.8-0.4+0.5±0.3)×10-7, where the first errors are statistical and the second are systematic, with the muon to electron ratios RK*=0.83±0.17±0.08 and RK=1.03±0.19±0. 06. © 2009 The American Physical Society.