Measurement of $J/ψ\toγη_{\rm c}$ decay rate and $η_{\rm c}$ parameters at KEDR

V. V. Anashin, V. M. Aulchenko, E. M. Baldin, A. K. Barladyan, A. Yu. Barnyakov, M. Yu. Barnyakov, S. E. Baru, I. Yu. Basok, I. V. Bedny, A. E. Blinov, V. E. Blinov, A. V. Bobrov, V. S. Bobrovnikov, A. V. Bogomyagkov, A. E. Bondar, A. R. Buzykaev, S. I. Eidelman, Yu. M. Glukhovchenko, V. V. Gulevich, D. V. Gusev, S. E. Karnaev, G. V. Karpov, S. V. Karpov, T. A. Kharlamova, V. A. Kiselev, S. A. Kononov, K. Yu. Kotov, E. A. Kravchenko, V. F. Kulikov, G. Ya. Kurkin, E. A. Kuper, E. B. Levichev, D. A. Maksimov, V. M. Malyshev, A. L. Maslennikov, A. S. Medvedko, O. I. Meshkov, S. I. Mishnev, I. I. Morozov, N. Yu. Muchnoi, V. V. Neufeld, S. A. Nikitin, I. B. Nikolaev, I. N. Okunev, A. P. Onuchin, S. B. Oreshkin, I. O. Orlov, A. A. Osipov, S. V. Peleganchuk, S. G. Pivovarov, P. A. Piminov, V. V. Petrov, A. O. Poluektov, G. E. Pospelov, V. G. Prisekin, O. L. Rezanova, A. A. Ruban, V. K. Sandyrev, G. A. Savinov, A. G. Shamov, D. N. Shatilov, B. A. Shwartz, E. A. Simonov, S. V. Sinyatkin, A. N. Skrinsky, V. V. Smaluk, A. V. Sokolov, A. M. Sukharev, E. V. Starostina, A. A. Talyshev, V. A. Tayursky, V. I. Telnov, Yu. A. Tikhonov, K. Yu. Todyshev, G. M. Tumaikin, Yu. V. Usov, A. I. Vorobiov, A. N. Yushkov, V. N. Zhilich, V. V. Zhulanov, A. N. Zhuravlev

Published 2014-06-30, updated 2014-10-22Version 2

Using the inclusive photon spectrum based on a data sample collected at the $J/\psi$ peak with the KEDR detector at the VEPP-4M $e^+e^-$ collider, we measured the rate of the radiative decay $J/\psi\to\gamma\eta_{\rm c}$ as well as $\eta_{\rm c}$ mass and width. Taking into account an asymmetric photon lineshape we obtained $\Gamma^0_{\gamma\eta_{\rm c}}=2.98\pm0.18 \phantom{|}^{+0.15}_{-0.33}$ keV, $M_{\eta_{\rm c}} = 2983.5 \pm 1.4 \phantom{|}^{+1.6}_{-3.6}$ MeV/$c^2$, $\Gamma_{\eta_{\rm c}} = 27.2 \pm 3.1 \phantom{|}^{+5.4}_{-2.6}$ MeV.