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

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 M e + e − > 0.15 GeV / c 2 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.

P. Braun-Munzinger | K. Lapidus | J. Stroth | J. Mousa | P. Finocchiaro | F. Krizek | J. S. Lange | I. Frohlich | H. Strobele | A. Tarantola | R. Trebacz | M. Destefanis | S. Spataro | L. Naumann | D. Belver | P. Cabanelas | W. Kuhn | P. Fonte | V. Pechenov | O. Pechenova | L. Fabbietti | A. Sadovsky | R. Holzmann | A. Gil | W. Koenig | B. Spruck | P. Tlusty | C. Gilardi | L. Maier | J. Pietraszko | T. Liu | O. V. Fateev | P. Salabura | W. Przygoda | J. Otwinowski | R. Krucken | B. Ramstein | V. Metag | M. Palka | A. Rustamov | T. Liu | A. Tarantola | P. Fonte | J. Lange | J. Mousa | E. Castro | M. Palka | M. Traxler | M. Destefanis | S. Chernenko | M. Sudoł | B. Spruck | C. Sturm | I. Frohlich | C. Muntz | J. Stroth | L. Naumann | A. Belyaev | M. Weber | P. Braun-Munzinger | L. Fabbietti | T. Karavicheva | F. Krizek | A. Kurepin | K. Lapidus | J. Otwinowski | Y. Pachmayer | A. Rustamov | A. Schmah | Y. Zanevsky | A. Reshetin | F. Guber | V. Wagner | S. Spataro | W. Kuhn | R. Gernhauser | A. Kugler | P. Zhou | A. Sadovsky | M. Jurkovič | A. Blanco | L. Lopes | L. Maier | J. Michel | P. Finocchiaro | P. Salabura | V. Metag | T. Hennino | B. Ramstein | R. Holzmann | D. Belver | R. Krucken | J. D'iaz | D. Gonz'alez-D'iaz | A. Ivashkin | V. Wagner | D. Gonz'alez-D'iaz | C. Sturm | J. Boyard | Y. Sobolev | J. Friese | T. Christ | M. Golubeva | S. Yurevich | O. Fateev | E. Castro | A. Balanda | A. Blanco | J. L. Boyard | T. Christ | F. Dohrmann | A. Dybczak | J. Friese | T. Galatyuk | T. Hennino | I. Iori | M. Jurkovic | D. Kirschner | I. Koenig | B. W. Kolb | R. Kotte | A. Kugler | S. Lang | A. Mangiarotti | B. Michalska | E. Schwab | M. Sudol | M. Traxler | M. Wisniowski | T. Wojcik | S. Yurevich | P. Zhou | F. Guber | T. Karavicheva | A. Kurepin | J. D'iaz | L. Lopes | Y. Parpottas | J. Michel | I. Iori | A. V. Belyaev | S. Chernenko | M. Golubeva | A. Ivashkin | M. Lorenz | J. Markert | Y. C. Pachmayer | Y. Parpottas | A. Reshetin | A. Schmah | K. Teilab | H. Tsertos | M. Weber | Y. V. Zanevsky | E. Morinière | C. Muntz | B. Kolb | P. Tlustý | T. Galatyuk | W. Koenig | J. Markert | J. Pietraszko | B. Kampfer | B. Michalska | J. Wustenfeld | The HADES Collaboration G. Agakishiev | M. Bohmer | J. A. Garz'on | R. Gernhauser | B. Kampfer | E. Moriniere | Yu.G. Sobolev | E. Schwab | A. Mangiarotti | R. Kotte | A. Balanda | P. Cabanelas | A. Dybczak | A. Gil | I. Koenig | M. Lorenz | V. Pechenov | O. Pechenova | W. Przygoda | K. Teilab | R. Trebacz | H. Tsertos | D. Kirschner | F. Dohrmann | S. Lang | M. Wiśniowski | T. Wójcik | C. Gilardi | M. Bohmer | H. Strobele | J. Wustenfeld | T. Liu | T. H. C. G. Agakishiev | J. Mousa | J. Lange | M. Palka | J. Michel

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