Exclusive measurement of the eta arrow right pi super(+) pi super(-) gamma decay

• Published in: Physics letters. B Vol. 707; no. 2; pp. 243 - 249
• Main Authors: Adolph, C, Augustyniak, W, Bardan, W, Bashkanov, M, Berlowski, M, Bhatt, H, Brinkmann, K-T, Buescher, M, Calen, H, Clement, H, Coderre, D, Czerwinski, E, Doroshkevich, E, Engels, R, Erven, W, Fohl, K, Fransson, K, Goldenbaum, F, Grigoryev, K, Heijkenskjold, L, Heimlich, J, Hejny, V, Hinterberger, F, Hodana, M, Hoistad, B, Jacewicz, M, Jany, A, Jany, B R, Jarczyk, L, Johansson, T, Kemmerling, G, Khakimova, O, Khoukaz, A, Klaja, J, Kleines, H, Klos, B, Kren, F, Krzemien, W, Kulessa, P, Kupsc, A, Lalwani, K, Leupold, S, Lorentz, B, Magiera, A, Maier, R, Marianski, B, Marciniewski, P, Meisner, U-G, Mikirtychiants, M, Morsch, H-P, Nandi, B K, Niedzwiecki, S, Ohm, H, Del Rio, EPerez, Petri, T, Petukhov, Y, Piskunov, N, Plucinski, P, Podkopal, P, Povtoreyko, A, Prasuhn, D, Pricking, A, Rausmann, T, Redmer, C F, Ritman, J, Roy, A, Rudy, Z, Sawant, S, Schadmand, S, Schmidt, A, Serdyuk, V, Shah, N, Siemaszko, M, Siudak, R, Skorodko, T, Skurzok, M, Smyrski, J, Sopov, V, Stepaniak, J, Stockhorst, H, Stollenwerk, F, Stroher, H, Szczurek, A, Taeschner, A, Terschluesen, C, Varma, R, Vlasov, P, Wagner, G J, Winnemoller, A, Wirzba, A, Wolke, M, Wuestner, P, Wurm, P, Yuan, X, Yurev, L, Zheng, C, Zielinski, MJ, Zipper, W, Zlomanczuk, J, Zupranski, P
• Format: Journal Article
• Language: English
• Published: 20-01-2012
• Subjects: Decay; Gages; Inclusions; Invariants; Mesons; Parametrization; Pions
• ISSN: 0370-2693
• DOI: 10.1016/j.physletb.2011.12.027

An exclusive measurement of the decay eta arrow right pi super(+) pi super(-) gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction [inline image] X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on [inline image] 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 eta arrow right pi super(+) pi super(-) gamma . 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 pi super(+) pi super(-) system.