1210.6914 (Belle Collaboration et al.)

Study of the Hadronic Transitions $Υ$(2S)$\rightarrow
(η,π^0)Υ$(1S) at Belle    [PDF]

Belle Collaboration, U. Tamponi, R. Mussa, I. Adachi, H. Aihara, D. M. Asner, V. Aulchenko, T. Aushev, A. M. Bakich, M. Barrett, B. Bhuyan, A. Bondar, A. Bozek, M. Bra\v, T. E. Browder, A. Chen, P. Chen, B. G. Cheon, K. Chilikin, I. -S. Cho, K. Cho, Y. Choi, J. Dalseno, Z. Dole\v, Z. Drásal, D. Dutta, S. Eidelman, D. Epifanov, S. Esen, H. Farhat, J. E. Fast, A. Frey, V. Gaur, R. Gillard, Y. M. Goh, B. Golob, K. Hayasaka, Y. Horii, Y. Hoshi, H. J. Hyun, T. Iijima, A. Ishikawa, Y. Iwasaki, I. Jaegle, J. H. Kang, T. Kawasaki, H. O. Kim, J. H. Kim, K. T. Kim, M. J. Kim, Y. J. Kim, J. Klucar, B. R. Ko, P. Kody\v, S. Korpar, R. T. Kouzes, P. Kri\v, P. Krokovny, T. Kumita, A. Kuzmin, S. -H. Lee, Y. Li, C. Liu, Y. Liu, Z. Q. Liu, D. Liventsev, H. Miyata, R. Mizuk, G. B. Mohanty, A. Moll, N. Muramatsu, M. Nakao, Z. Natkaniec, C. Ng, S. Nishida, O. Nitoh, S. Ogawa, T. Ohshima, S. Okuno, S. L. Olsen, Y. Onuki, P. Pakhlov, H. K. Park, K. S. Park, T. K. Pedlar, R. Pestotnik, M. Petri\v, L. E. Piilonen, M. Röhrken, Y. Sakai, S. Sandilya, D. Santel, L. Santelj, T. Sanuki, O. Schneider, G. Schnell, C. Schwanda, K. Senyo, C. P. Shen, T. -A. Shibata, J. -G. Shiu, B. Shwartz, F. Simon, P. Smerkol, Y. -S. Sohn, A. Sokolov, E. Solovieva, M. Stari\v, T. Sumiyoshi, K. Tanida, N. Taniguchi, G. Tatishvili, Y. Teramoto, K. Trabelsi, S. Uehara, S. Uno, C. Van Hulse, P. Vanhoefer, G. Varner, C. H. Wang, M. -Z. Wang, P. Wang, X. L. Wang, M. Watanabe, Y. Watanabe, K. M. Williams, E. Won, B. D. Yabsley, Y. Yamashita, C. Z. Yuan, Z. P. Zhang, V. Zhilich, V. Zhulanov, A. Zupanc

We study the rare hadronic transitions $\Upsilon(2S)\rightarrow \Upsilon(1S)\eta$ and $\Upsilon(2S)\rightarrow \Upsilon(1S)\pi^0$ using a sample of 158 $\times 10^6$ $\Upsilon(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe the $\eta$ meson decay to $\gamma\gamma$ and $\pi^+\pi^-\pi^0$ final states; the $\Upsilon(1S)$ is reconstructed in the $\mu^+\mu^-$ and $e^+e^-$ decay modes. We measure the ratios of branching fractions (${\mathcal B}$) $\frac{{\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\eta)}{{\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\pi^+\pi^-)}$ = (1.99$\pm$0.14 (stat) $\pm$0.11 (syst)) $\times 10^{-3}$ and $\frac{{\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\pi^0)}{{\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\pi^+\pi^-)} < 2.3 \times 10^{-4}$ at the 90% confidence level (CL). Assuming the value ${\mathcal B}(\Upsilon(2S) \rightarrow \Upsilon(1S)\pi^-\pi^+)$ = (17.92$\pm$0.26)%, we obtain $ {\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\eta) = (3.57 \pm 0.25 ({\rm stat})\ \pm 0.21 ({\rm syst}))\times 10^{-4} $ and $ {\mathcal B}(\Upsilon(2S)\rightarrow\Upsilon(1S)\pi^0) < 4.1\times 10^{-5}\ ({\rm 90%\ CL}). $

View original: http://arxiv.org/abs/1210.6914