Spin Dependence of eta Meson Production in Proton-Proton Collisions Close to Threshold

WASA-At-COSY Collaboration, P. Adlarson*, W. Augustyniak, W. Bardan, M. Bashkanov, S. D. Bass, F. S. Bergmann, M. Berlowski, A. Bondar, M. Buscher, H. Calen, I. Ciepal, H. Clement, E. Czerwinski, K. Demmich, R. Engels, A. Erven, W. Erven, W. Eyrich, P. FedoretsK. Fohl, K. Fransson, F. Goldenbaum, A. Goswami, K. Grigoryev, C. -O. Gullstrom, L. Heijkenskjold, V. Hejny, N. Husken, L. Jarczyk, T. Johansson, B. Kamys, G. Kemmerling, G. Khatri, A. Khoukaz, O. Khreptak, D. A. Kirillov, S. Kistryn, H. Kleines, B. Klos, W. Krzemien, P. Kulessa, A. Kupsc, A. Kuzmin, K. Lalwani, D. Lersch, B. Lorentz, A. Magiera, R. Maier, P. Marciniewski, B. Marianski

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high polarization degree of the proton beam of COSY, the reaction (p) over right arrowp -> pp eta has been measured close to threshold to explore the analyzing power A(y). The angular distribution of A(y) is determined with the precision improved by more than 1 order of magnitude with respect to previous results, allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV, signaling s-wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveal strong interference of Ps and Pp partial waves and cancellation of (Pp)(2) and Ss*Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the eta meson.

Original languageEnglish
Article number022002
Number of pages6
JournalPhysical Review Letters
Issue number2
Publication statusPublished - 8 Jan 2018


  • COSY


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