Dielectron Production in 12C + 12C Collisions at 2A GeV with the HADES Spectrometer

Agakichiev, G.; Agodi, C.; Alvarez Pol, H.; Bałanda, A.; Bertini, D.; Bielcik, J.; Bellia, G.; Boehmer, M.; Bokemeyer, H.; Boyard, J. L.; Braun Munzinger, P.; Cabanelas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Cosentino, L.; Dıaz, J.; Dohrmann, F.; Duran, I.; Eberl, T.; Enghardt, W.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Froehlich, I.; Fuentes, B.; Garabatos, C.; Garzon, J. A.; Gernhauser, R.; Gilardi, 12 C.; Golubeva, M.; Gonzalez Dıaz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Homolka, J.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jaskuła, M.; Jurkovic, M.; Kagarlis, M.; Kajetanowicz, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kastenmueller, A.; Kidon, L.; Kienle, P.; Koenig, I.; Koenig, W.; Koerner, H. J.; Kolb, B. W.; Kotte, R.; Kruecken, R.; Kugler, A.; Kuehn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lange, S.; Lehnert, J.; Lins, E.; Magestro, D.; Maiolino, C.; Malarz, A.; Markert, J.; Metag, V.; Mousa, J.; Muench, M.; Muentz, C.; Naumann, L.; Nekhaev, A.; Novotny, J.; Otwinowski, J.; Pachmayer, Y. C.; Pechenov, V.; Perez, T.; Piattelli, P.; Pietraszko, J.; Pleskac, R.; Płoskon, M.; Pospısil, V.; Prokopowicz, W.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Schoen, H.; Schoen, W.; Schroeder, C.; Schwab, E.; Simon, R. S.; Smolyankin, V.; Smykov, L.; Spataro, STEFANO GIOVANNI; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudoł, M.; Suk, M.; Taranenko, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vassiliev, D.; Vazquez, A.; Wagner, V.; Walus, W.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Zanevsky, Y.; Zeitelhack, K.; Zovinec, D.; Zumbruch, P.

doi:10.1103/PhysRevLett.98.052302

The invariant-mass spectrum of e+e- pairs produced in 12C + 12C collisions at an incident energy of 2 GeV per nucleon has been measured for the first time. The measured pair production probabilities span over 5 orders of magnitude from the pi°-Dalitz to the rho/omega invariant-mass region. Dalitz decays of pi° and eta account for all the yield up to 0:15 GeV=c2, but for only about 50% above this mass. A comparison with model calculations shows that the excess pair yield is likely due to baryon-resonance and vector-meson decays. Transport calculations based on vacuum spectral functions fail, however, to describe the entire mass region.