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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2006, vol. 97, p. -

Evidence of the purely leptonic decay B-→τ-ν̄τ

Ikado K., Abe K., Abe K., Adachi I., Aihara H., Akai K., Akemoto M., Anipko D., Arinstein K., Aulchenko V., Aushev T., Aziz T., Bakich A. M., Balagura V., Barbero M., Bay A., Bedny I., Belous K., Bitenc U., Bizjak I., Bondar A., Bozek A., Bračko M., Browder T. E., Chang P., Chen A., Chen W. T., Choi Y., Cole S., Dalseno J., Danilov M., Dash M., Eidelman S., Epifanov D., Flanagan J., Fratina S., Furukawa K., Gabyshev N., Gershon T., Go A., Gokhroo G., Golob B., Gorišek A., Ha H., Haba J., Hara K., Hara T., Hastings N. C., Hayasaka K., Hayashii H., Hazumi M., Hinz L., Hokuue T., Hoshi Y., Hou S., Hou W. S., Iida N., Iijima T., Imoto A., Inami K., Ishikawa A., Ishino H., Itoh R., Iwasaki M., Iwasaki Y., Kamitani T., Kang J. H., Kataoka S. U., Katayama N., Kawai H., Kawasaki T., Kichimi H., Kikutani E., Kim H. J., Kim H. O., Kinoshita K., Koiso H., Korpar S., Križan P., Krokovny P., Kulasiri R., Kumar R., Kuo C. C., Kuzmin A., Kwon Y. J., Lange J. S., Leder G., Lee J., Lesiak T., Limosani A., Lin S. W., Liventsev D., Marlow D., Matsumoto T., Matyja A.

We present the first evidence of the decay B-→τ-ν̄τ, using 414fb-1 of data collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We detect the signal with a significance of 3.5 standard deviations including systematics and measure the branching fraction to be B(B-→τ-ν̄τ)=(1.79-0.49+0.56(stat) -0.51+0.46(syst))×10-4. This implies that fB=0.229-0.031+0.036(stat)-0. 037+0.034(syst)GeV and is the first direct measurement of this quantity. © 2006 The American Physical Society.