2018•Physical review. D/Physical review. D.Open access
Measurement of ηc(1S) , ηc(2S) , and nonresonant η′π+π− production via two-photon collisions
Q. N. Xu, Ichiro Adachi, H. Aihara, S. Al Said, David M. Asner, H. Atmacan, V. Aulchenko, T. Aushev, Rachid Ayad, V. Babu, I. Badhrees, A. M. Bakich, Vikas Bansal, E. L. Barberio, P. K. Behera, Miles Berger, Vishal Bhardwaj, B. Bhuyan, J. P. Biswal, A. Bondar, Andrzej Bozek, M. Bračko, D. Červenkov, A. Chen, B. G. Cheon, K. Chilikin, K. Cho, S. K. Choi, Y. Choi, D. Cinabro, S. Cunliffe, T. Czank, Nibedita Dash, S. Di Carlo, Z. Doležal, Zbyněk Drásal, S. Eidelman, Denis A. Epifanov, James Elliot Fast, T. Ferber, B. G. Fulsom, R. B. Garg, V. Gaur, N. Gabyshev, Alexey Garmash, Michael H. Gelb, P. Goldenzweig, Y. Guan, E. Guido, J. Haba, K. Hayasaka, Hisaki Hayashii, M. T. Hedges, W.-S. Hou, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, M. Iwasaki, M. Iwasaki, I. Jaeglé, H. B. Jeon, Yaochu Jin, K. K. Joo, T. Julius, A. B. Kaliyar, K. H. Kang, G. Karyan, T. Kawasaki, H. Kichimi, C. Kiesling, D. Y. Kim, H. J. Kim, J. B. Kim, P. Kodyš, S. Korpar, D. Kotchetkov, P. Križan, R. S. Kroeger, P. Krokovny, R. Kulasiri, Y.-J. Kwon, I. S. Lee, S. C. Lee, L. K. Li, Y. Li, L. Li Gioi, James Frederick Libby, Dmitri Liventsev, M. Lubej, Tao Luo, M. Masuda, T. Matsuda, Dmitry V. Matvienko, Mario Merola, Kenkichi Miyabayashi, H. Miyata, R. Mizuk, H. K. Moon, T. Mori, R. Mussa, T. Nanut, K. J. Nath, Z. Natkaniec, M. Nayak, N. K. Nisar, Shohei Nishida, S. Okuno, Hiroaki ONO, Y. Onuki, Pavel N. Pakhlov, Galina V. Pakhlova, B. Pal, H. Park, Stephan Martin Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, V. Popov, Martin Ritter, Armine Rostomyan, Guido Russo, Y. Sakai, M. Salehi, Saurabh Sandilya, T. Sanuki, V. Savinov, O. Schneider, G. Schnell, Christoph Schwanda, Y. Seino, Katsumi Senyo, O. Seon, Martin E. Sevior, V. Shebalin, Chun Shen, T.-A. Shibata, N. Shimizu, J.-G. Shiu, A. Sokolov, Elena Solovieva, Marko Starič, J. Strube, Takayuki Sumiyoshi, Makoto Takizawa, Umberto Tamponi, Kiyoshi Tanida, Francesco Tenchini, Makoto Uchida, S. Uehara, Timofey Uglov, Y. Unno, S. Uno, P. Urquijo, C. Van Hulse, Gary S. Varner, A. Vinokurova, V. Vorobyev, A. Vossen, B. Wang, C. H. Wang, M.-Z. Wang, P. Wang, X. L. Wang, M. Watanabe, Y. Watanabe, E. Widmann, Eunil Won, H. Ye, C. Z. Yuan, Yosuke Yusa, S. Zakharov, C. C. Zhang, Z. P. Zhang, V. N. Zhilich, Valentina I. Zhukova, Vladimir V. Zhulanov, Anže Zupanc
Abstract
We report the measurement of $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}(1S),{\ensuremath{\eta}}_{c}(2S)\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ with ${\ensuremath{\eta}}^{\ensuremath{'}}$ decays to $\ensuremath{\gamma}\ensuremath{\rho}$ and $\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ using $941\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The ${\ensuremath{\eta}}_{c}(1S)$ mass and width are measured to be $M=[2984.6\ifmmode\pm\else\textpm\fi{}0.7\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}2.2\text{ }(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.3\text{ }(\mathrm{model})]\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and $\mathrm{\ensuremath{\Gamma}}=[30.{8}_{\ensuremath{-}2.2}^{+2.3}\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}2.5\text{ }(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}1.4\text{ }(\mathrm{model})]\text{ }\text{ }\mathrm{MeV}$, respectively. First observation of ${\ensuremath{\eta}}_{c}(2S)\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ with a significance of $5.5\ensuremath{\sigma}$ including systematic error is obtained, and the ${\ensuremath{\eta}}_{c}(2S)$ mass is measured to be $M=[3635.1\ifmmode\pm\else\textpm\fi{}3.7\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}2.9\text{ }(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.4\text{ }(\mathrm{model})]\text{ }\text{ }\mathrm{MeV}/{c}^{2}$. The products of the two-photon decay width and branching fraction ($\mathcal{B}$) of decays to ${\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ are determined to be ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}$${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}\mathcal{B}=[65.4\ifmmode\pm\else\textpm\fi{}2.6\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}7.8\text{ }\text{ }(\mathrm{syst})]\text{ }\text{ }\mathrm{eV}$ for ${\ensuremath{\eta}}_{c}(1S)$ and $[{5.6}_{\ensuremath{-}1.1}^{+1.2}\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.1\text{ }(\mathrm{syst})]\text{ }\text{ }\mathrm{eV}$ for ${\ensuremath{\eta}}_{c}(2S)$. The cross sections for $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}{f}_{2}(1270)$ are measured for the first time.