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Exclusive measurement of the η → π + π − γ decay

2011; Elsevier BV; Volume: 707; Issue: 2 Linguagem: Inglês

10.1016/j.physletb.2011.12.027

1873-2445

P. Adlarson, C. Adolph, W. Augustyniak, W. Bardan, M. Bashkanov, T. Bednarski, Florian Bergmann, M. Berłowski, H. Bhatt, K.-Th. Brinkmann, M. Büscher, H. Calén, H. Clement, D. Coderre, E. Czerwiński, E. Doroshkevich, R. Engels, W. Erven, W. Eyrich, P. Fedorets, K. Föhl, K. Fransson, F. Goldenbaum, P. Goslawski, K. Grigoryev, C.-O. Gullström, C. Hanhart, L. Heijkenskjöld, J. Heimlich, V. Hejny, F. Hinterberger, M. Hodana, B. Höistad, M. Jacewicz, A. Jany, Benedykt R. Jany, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, O. Khakimova, A. Khoukaz, St. Kistryn, J. Klaja, H. Kleines, B. Kłos, F. Kren, W. Krzemień, P. Kulessa, A. Kupść, K. Lalwani, Stefan Leupold, B. Lorentz, A. Magiera, R. Maier, B. Mariański, P. Marciniewski, Ulf-G. Meißner, M. Mikirtychiants, H.P. Morsch, P. Moskal, Basanta Kumar Nandi, Szymon Niedźwiecki, H. Ohm, A. Passfeld, C. Pauly, E. Pérez del Río, Thimo Petri, Y. Petukhov, Н. М. Пискунов, P. Pluciński, P. Podkopał, A. Povtoreyko, D. Prasuhn, A. Pricking, K. Pysz, A. Pyszniak, T. Rausmann, C. F. Redmer, J. Ritman, A. Roy, Z. Rudy, S. Sawant, S. Schadmand, A. Schmidt, T. Sefzick, V. Serdyuk, Nausheen R. Shah, M. Siemaszko, R. Siudak, T. Skorodko, M. Skurzok, J. Smyrski, V. Sopov, R. Stassen, J. Steṕaniak, G. Sterzenbach, H. Stockhorst, Felix Stollenwerk, H. Ströher, Antoni Szczurek, A. Täschner, Carla Terschlüsen, T. Tolba, A. Trzciński, R. Varma, P. Vlasov, G. J. Wagner, W. Węglorz, A. Winnemöller, A. Wirzba, M. Wolke, A. Wrońska, P. Wüstner, P. Wurm, X. Yuan, L. Yurev, J. Zabierowski, C. Zheng, M. Zieliński, W. Zipper, J. Złomańczuk, P. Żuprański,

High-Energy Particle Collisions Research

An exclusive measurement of the decay η→π+π−γ has been performed at the WASA facility at COSY. The η mesons were produced in the fusion reaction pd→He3 X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13960±140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of η→π+π−γ. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the π+π− system.