1206.5087 (C. C. Zhang et al.)

First study of η_c, η(1760) and X(1835) production via
η'π^+π^- final states in two-photon collisions    [PDF]

C. C. Zhang, H. Aihara, D. M. Asner, T. Aushev, A. M. Bakich, Y. Ban, K. Belous, M. Bischofberger, T. E. Browder, A. Chen, B. G. Cheon, K. Chilikin, R. Chistov, Y. Choi, J. Dalseno, M. Danilov, S. Eidelman, M. Feindt, V. Gaur, N. Gabyshev, Y. M. Goh, Y. L. Han, H. Hayashii, Y. Horii, W. S. Hou, H. J. Hyun, T. Iijima, K. Inami, A. Ishikawa, M. Iwabuchi, T. Julius, C. Kiesling, H. O. Kim, M. J. Kim, Y. J. Kim, B. R. Ko, P. Kodyš, S. Korpar, P. Krokovny, A. Kuzmin, J. Li, J. Libby, Y. Liu, Z. Q. Liu, R. Louvot, D. Matvienko, S. McOnie, R. Mizuk, E. Nakano, M. Nakao, H. Nakazawa, Z. Natkaniec, S. Nishida, T. Ohshima, S. Okuno, S. L. Olsen, P. Pakhlov, G. Pakhlova, H. Park, H. K. Park, R. Pestotnik, M. Petrič, L. E. Piilonen, M. Röhrken, S. Ryu, H. Sahoo, Y. Sakai, D. Santel, T. Sanuki, O. Schneider, C. Schwanda, M. E. Sevior, M. Shapkin, V. Shebalin, C. P. Shen, T. A. Shibata, J. G. Shiu, B. Shwartz, P. Smerkol, Y. -S. Sohn, E. Solovieva, S. Stanič, M. Starič, M. Sumihama, T. Sumiyoshi, I. Tikhomirov, M. Uchida, S. Uehara, T. Uglov, Y. Unno, S. Uno, G. Varner, A. Vinokurova, V. Vorobyev, P. Wang, X. L. Wang, Y. Watanabe, K. M. Williams, B. D. Yabsley, Y. Yamashita, C. Z. Yuan, Z. P. Zhang, V. Zhulanov

The invariant mass spectrum of the \eta' \pi^+ \pi^- final state produced in two-photon collisions is obtained using a 673 fb^{-1} data sample collected in the vicinity of the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a clear signal of the \eta_c and measure its mass and width to be M(\eta_c)=(2982.7 +- 1.8(stat) +- 2.2(syst) +- 0.3(model)) MeV/c^2 and \Gamma(\eta_c) = (37.8^{+5.8}_{-5.3}(stat) +- 2.8(syst) +- 1.4(model)) MeV/c^2. The third error is an uncertainty due to possible interference between the \eta_c and a non-resonant component. We also report the first evidence for \eta(1760) decay to \eta' \pi^+ \pi^-; we find two solutions for its parameters, depending on the inclusion or not of the X(1835), whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent X(1835) and \eta(1760) resonant amplitudes, we set a 90% confidence level upper limit on the product \Gamma_{\gamma\gamma} \BR (\eta' \pi^+ \pi^-) for the X(1835).

View original: http://arxiv.org/abs/1206.5087