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arXiv · 0910.5875

Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

The HADES Collaboration·G. Agakishiev·A. Balanda·D. Belver·A. V. Belyaev·A. Blanco·M. Böhmer·J. L. Boyard·P. Braun-Munzinger·P. Cabanelas·E. Castro·S. Chernenko·T. Christ·M. Destefanis·J. Díaz·F. Dohrmann·A. Dybczak·L. Fabbietti·O. V. Fateev·P. Finocchiaro·P. Fonte·J. Friese·I. Fröhlich·T. Galatyuk·J. A. Garzón·R. Gernhäuser·A. Gil·C. Gilardi·M. Golubeva·D. González-Díaz·F. Guber·T. Hennino·R. Holzmann·I. Iori·A. Ivashkin·M. Jurkovic·B. Kämpfer·T. Karavicheva·D. Kirschner·I. Koenig·W. Koenig·B. W. Kolb·R. Kotte·F. Krizek·R. Krücken·W. Kühn·A. Kugler·A. Kurepin·S. Lang·J. S. Lange·K. Lapidus·T. Liu·L. Lopes·M. Lorenz·L. Maier·A. Mangiarotti·J. Markert·V. Metag·B. Michalska·J. Michel·E. Morinière·J. Mousa·C. Müntz·L. Naumann·J. Otwinowski·Y. C. Pachmayer·M. Palka·Y. Parpottas·V. Pechenov·O. Pechenova·J. Pietraszko·W. Przygoda·B. Ramstein·A. Reshetin·A. Rustamov·A. Sadovsky·P. Salabura·A. Schmah·E. Schwab·Yu. G. Sobolev·S. Spataro·B. Spruck·H. Ströbele·J. Stroth·C. Sturm·M. Sudol·A. Tarantola·K. Teilab·P. Tlusty·M. Traxler·R. Trebacz·H. Tsertos·V. Wagner·M. Weber·M. Wisniowski·T. Wojcik·J. Wüstenfeld·S. Yurevich·Y. V. Zanevsky·P. Zhou
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Abstract

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

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The HADES Collaboration, G. Agakishiev, A. Balanda, D. Belver, A. V. Belyaev, A. Blanco, M. Böhmer, J. L. Boyard, P. Braun-Munzinger, P. Cabanelas, E. Castro, S. Chernenko, T. Christ, M. Destefanis, J. Díaz, F. Dohrmann, A. Dybczak, L. Fabbietti, O. V. Fateev, P. Finocchiaro, P. Fonte, J. Friese, I. Fröhlich, T. Galatyuk, J. A. Garzón, R. Gernhäuser, A. Gil, C. Gilardi, M. Golubeva, D. González-Díaz, F. Guber, T. Hennino, R. Holzmann, I. Iori, A. Ivashkin, M. Jurkovic, B. Kämpfer, T. Karavicheva, D. Kirschner, I. Koenig, W. Koenig, B. W. Kolb, R. Kotte, F. Krizek, R. Krücken, W. Kühn, A. Kugler, A. Kurepin, S. Lang, J. S. Lange, K. Lapidus, T. Liu, L. Lopes, M. Lorenz, L. Maier, A. Mangiarotti, J. Markert, V. Metag, B. Michalska, J. Michel, E. Morinière, J. Mousa, C. Müntz, L. Naumann, J. Otwinowski, Y. C. Pachmayer, M. Palka, Y. Parpottas, V. Pechenov, O. Pechenova, J. Pietraszko, W. Przygoda, B. Ramstein, A. Reshetin, A. Rustamov, A. Sadovsky, P. Salabura, A. Schmah, E. Schwab, Yu. G. Sobolev, S. Spataro, B. Spruck, H. Ströbele, J. Stroth, C. Sturm, M. Sudol, A. Tarantola, K. Teilab, P. Tlusty, M. Traxler, R. Trebacz, H. Tsertos, V. Wagner, M. Weber, M. Wisniowski, T. Wojcik, J. Wüstenfeld, S. Yurevich, Y. V. Zanevsky, P. Zhou. 2009-10-30. Origin of the low-mass electron pair excess in light nucleus-nucleus collisions. https://doi.org/10.1016/j.physletb.2010.05.010

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