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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2003, vol. 68, p. -

Vidence for CP-violating asymmetries in B 0→π +π - decays and constraints on the CKM angle φ 2

Abe K., Abe K., Abe N., Abe T., Adachi I., Aihara H., Akai K., Akatsu M., Akemoto M., Asano Y., Aushev T., Bakich A. M., Ban Y., Banas E., Bay A., Bedny I., Behera P. K., Bizjak I., Bondar A., Bozek A., Bračko M., Brodzicka J., Browder T. E., Casey B. C K, Chang P., Chen K. F., Cheon B. G., Chistov R., Choi S. K., Choi Y., Choi Y. K., Danilov M., Dragic J., Drutskoy A., Eidelman S., Eiges V., Everton C. W., Flanagan J., Fukunaga C., Furukawa K., Gabyshev N., Garmash A., Gershon T., Golob B., Guo R., Hagner C., Hara K., Hastings N. C., Hasuko K., Hayashii H., Hazumi M., Higuchi T., Hinz L., Hojo T., Hokuue T., Hoshi Y., Hou W. S., Hsiung Y. B., Huang H. C., Igaki T., Igarashi Y., Iijima T., Ikeda H., Inami K., Ishikawa A., Ishino H., Itoh R., Iwasaki H., Iwasaki Y., Jang H. K., Kang J. S., Kapusta P., Kataoka S. U., Katayama N., Katano G., Kawai H., Kawamura N., Kawasaki T., Kichimi H., Kikuchi M., Kikutani E., Kim D. W., Kim H. J., Kim H. O., Kim H., Kim J. H., Kim S. K., Kobayashi S., Korpar S., Križan P., Krokovny P., Kubo T., Kulasiri R., Kumar S., Kuzmin A.

We present an improved measurement of CP-violating asymmetries in B 0→π +π - decays based on a 78 fb -1 data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. We reconstruct one neutral B meson as a B 0→π +π - CP eigenstate and identify the flavor of the accompanying B meson from inclusive properties of its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the CP-violating asymmetry amplitudes A ππ= +0.77 ±0.27(stat) ±0.08(syst) and S ππ=-1.23 ±0.41(stat) -0.07 +0.08(syst), where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for CP-violating asymmetry parameters A ππ and S ππ based on a frequentist approach. We rule out the CP-conserving case, A ππ=S ππ=0, at the 99.93% confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle φ 2. © 2003 The American Physical Society.