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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2007, vol. 98, p. -

Observation of direct CP violation in B0→π+π- decays and model-independent constraints on the quark-mixing angle 2

Ishino H., Abe K., Abe K., Adachi I., Aihara H., Anipko D., Arinstein K., Aushev T., Bakich A. M., Barberio E., Barbero M., Bedny I., Bitenc U., Bizjak I., Blyth S., Bozek A., Bračko M., Browder T. E., Chang M. C., Chang P., Chao Y., Chen A., Chen K. F., Chen W. T., Cheon B. G., Chistov R., Choi Y., Choi Y. K., Cole S., Dalseno J., Dash M., Drutskoy A., Eidelman S., Fratina S., Gershon T., Go A., Gokhroo G., Golob B., Gorišek A., Ha H., Haba J., Hara K., Hayasaka K., Hazumi M., Heffernan D., Hokuue T., Hoshi Y., Hou S., Hsiung Y. B., Iijima T., Imoto A., Inami K., Ishikawa A., Iwasaki Y., Kang J. H., Kapusta P., Kataoka S. U., Katayama N., Kawai H., Kawasaki T., Khan H. R., Kibayashi A., Kichimi H., Kinoshita K., Korpar S., Križan P., Krokovny P., Kulasiri R., Kumar R., Kuo C. C., Kusaka A., Kuzmin A., Kwon Y. J., Lee M. J., Lee S. E., Lesiak T., Limosani A., Lin S. W., MacNaughton J., Mandl F., Marlow D., Matsumoto T., Matyja A., McOnie S., Mitaroff W., Miyabayashi K., Miyake H., Miyata H., Miyazaki Y., Mizuk R., Mohapatra D., Nagasaka Y., Nakano E., Nakao M.

We report a new measurement of the time-dependent CP-violating parameters in B0→π+π- decays with 535×106 BB̄ pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Υ(4S) resonance. We find 1464±65 B0→π+π- events and measure the CP-violating parameters Sππ=-0.61±0.10(stat)±0. 04(syst) and Aππ=+0.55±0.08(stat)±0.05(syst). We observe large direct CP violation with a significance greater than 5 standard deviations for any Sππ value. Using isospin relations, we measure the Cabibbo-Kobayashi-Maskawa quark-mixing matrix angle 2=(97±11)° for the solution consistent with the standard model and exclude the range 11°< 2<79° at the 95% confidence level. © 2007 The American Physical Society.