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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2009, vol. 79, p. -

Observation of B0→ΛΛ̄K0 and B0→Λ Λ̄K*0 at Belle

Chang Y. W., Wang M. Z., Adachi I., Aihara H., Aushev T., Bakich A. M., Balagura V., Bay A., Bhardwaj V., Bitenc U., Bondar A., Bozek A., Bračko M., Browder T. E., Chao Y., Chen A., Chistov R., Choi Y., Dalseno J., Danilov M., Dash M., Drutskoy A., Eidelman S., Goldenzweig P., Ha H., Han B. Y., Hara T., Hayasaka K., Hayashii H., Hazumi M., Heffernan D., Horii Y., Hoshi Y., Hou W. S., Hyun H. J., Inami K., Ishikawa A., Iwasaki M., Iwasaki Y., Joshi N. J., Kah D. H., Kang J. H., Kawai H., Kawasaki T., Kichimi H., Kim H. J., Kim Y. I., Kim Y. J., Ko B. R., Korpar S., Križan P., Kwon Y. J., Kyeong S. H., Lee J. S., Lee M. J., Lee S. E., Lesiak T., Limosani A., Lin S. W., Liu C., Liu Y., Louvot R., Mandl F., Matyja A., McOnie S., Miyabayashi K., Miyata H., Miyazaki Y., Mizuk R., Nagasaka Y., Nakao M., Natkaniec Z., Nishida S., Nitoh O., Ogawa S., Okuno S., Ozaki H., Pakhlov P., Pakhlova G., Park C. W., Park H. K., Park K. S., Peak L. S., Pestotnik R., Piilonen L. E., Rozanska M., Sahoo H., Sakai Y., Schneider O., Sekiya A., Senyo K., Shapkin M., Shiu J. G., Shwartz B., Singh J. B.

We study the charmless decays B→ΛΛ̄h, where h stands for π+, K+, K0,K*+, or K*0, using a 605fb-1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. We observe B0→ΛΛ̄K0 and B0→ΛΛ̄K*0 with branching fractions of (4.76-0.68+0.84(stat)±0.61(syst))×10-6 and (2.46-0.72+0. 87±0.34)×10-6, respectively. The significances of these signals in the threshold-mass enhanced mass region, MΛΛ̄<2.85GeV/c2, are 12.4σ and 9.3σ, respectively. We also update the branching fraction B(B+→ΛΛ̄K+)=(3.38-0.36+0.41±0.41) ×10-6 with better accuracy, and report the following measurement or 90% confidence level upper limit in the threshold-mass-enhanced region: B(B+→ΛΛ̄K*+)=(2.19-0.88+1.13±0.33) ×10-6 with 3.7σ significance; B(B+→ΛΛ̄π+) <0.94×10-6. A related search for B0→ΛΛ̄D̄0 yields a branching fraction B(B0→ΛΛ̄D̄0)=(1.05-0. 44+0.57±0.14)×10-5. This may be compared with the large, ∼10-4, branching fraction observed for B0→pp̄D̄0. The MΛΛ̄ enhancements near threshold and related angular distributions for the observed modes are also reported. © 2009 The American Physical Society.