Measurement of the η → 3 π 0 Dalitz plot distribution with the WASA detector at COSY WASA-at-COSY Collaboration

a Physikalisches Institut, Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany b Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich, Germany c Jülich Center for Hadron Physics, Forschungszentrum Jülich, 52425 Jülich, Germany d Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany e The Few Body System Laboratory, High Energy Physics Division, St. Petersburg Nuclear Physics Institute, Orlova Rosha 2, 188300 Gatchina, Russia f High Energy Physics Department, The Andrzej Soltan Institute for Nuclear Studies, ul. Hoza 69, 00-681, Warsaw, Poland g Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 Maharashtra, India h Helmholtz-Institut für Strahlenund Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Nußallee 14-16, 53115 Bonn, Germany i Budker Institute of Nuclear Physics, akademika Lavrentieva prospect 11, 630090 Novosibirsk, Russia j Division of Nuclear and Particle Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden k Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Kraków, Poland l The Svedberg Laboratory, Uppsala University, Box 533, 75121 Uppsala, Sweden m Zentralinstitut für Elektronik, Forschungszentrum Jülich, 52425 Jülich, Germany n Institute for Theoretical and Experimental Physics, State Scientific Center of the Russian Federation, Bolshaya Cheremushkinskaya 25, 117218 Moscow, Russia o Cryogenic and Superconductive Techniques Department, High Energy Physics Division, St. Petersburg Nuclear Physics Institute, Orlova Rosha 2, 188300 Gatchina, Russia p Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 9, 48149 Münster, Germany q High Energy Accelerator Research Organisation KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan r August Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland s The Henryk Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, 152 Radzikowskiego St, 31-342 Kraków, Poland t Fachbereich Physik, Universität Duisburg-Essen, Lotharstr. 1, 47048 Duisburg, Germany u Bethe Center for Theoretical Physics, Rheinische Friedrich-Wilhelms-Universität Bonn, 53115 Bonn, Germany v Veksler and Baldin Laboratory of High Energiy Physics, Joint Institute for Nuclear Physics, 141980 Dubna, Russia w Department of Cosmic Ray Physics, The Andrzej Soltan Institute for Nuclear Studies, ul. Uniwersytecka 5, 90-950 Lodz, Poland x Institut für Experimentalphysik der Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany y Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Physics, 141980 Dubna, Russia z Department of Nuclear Reactions, The Andrzej Soltan Institute for Nuclear Studies, ul. Hoza 69, 00-681 Warsaw, Poland aa Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Rd., 730000 Lanzhou, China ab Department of Physics Applications, The Andrzej Soltan Institute for Nuclear Studies, 05-400 Otwock–Świerk, Poland