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. B\"ohmer , J. L. Boyard , P. Braun-Munzinger

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P. Cabanelas E. Castro S. Chernenko T. Christ M. Destefanis J. D\'iaz F. Dohrmann A. Dybczak L. Fabbietti O. V. Fateev P. Finocchiaro P. Fonte J. Friese I. Fr\"ohlich T. Galatyuk J. A. Garz\'on R. Gernh\"auser A. Gil C. Gilardi M. Golubeva D. Gonz\'alez-D\'iaz F. Guber T. Hennino R. Holzmann I. Iori A. Ivashkin M. Jurkovic B. K\"ampfer T. Karavicheva D. Kirschner I. Koenig W. Koenig B. W. Kolb R. Kotte F. Krizek R. Kr\"ucken W. K\"uhn 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. Morini\`ere J. Mousa C. M\"untz 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. Str\"obele 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. W\"ustenfeld S. Yurevich Y. V. Zanevsky P. Zhou

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classification ⚛️ nucl-ex

keywords electronpairreactionscollisionselementarylightpairsproduction

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

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