1205.1918 (G. Agakishiev et al.)

First measurement of low momentum dielectrons radiated off cold nuclear
matter    [PDF]

G. Agakishiev, A. Balanda, D. Belver, A. Belyaev, J. C. Berger-Chen, A. Blanco, M. Böhmer, J. L. Boyard, P. Cabanelas, S. Chernenko, A. Dybczak, E. Epple, L. Fabbietti, O. Fateev, P. Finocchiaro, P. Fonte, J. Friese, I. Fröhlich, T. Galatyuk, J. A. Garzón, R. Gernhäuser, K. Göbel, M. Golubeva, D. González-Díaz, F. Guber, M. Gumberidze, T. Heinz, T. Hennino, R. Holzmann, A. Ierusalimov, I. Iori, A. Ivashkin, M. Jurkovic, B. Kämpfer, T. Karavicheva, I. Koenig, W. Koenig, B. W. Kolb, G. Kornakov, R. Kotte, A. Krása, F. Krizek, R. Krücken, H. Kuc, W. Kühn, A. Kugler, A. Kurepin, V. Ladygin, R. Lalik, S. Lang, K. Lapidus, A. Lebedev, T. Liu, L. Lopes, M. Lorenz, L. Maier, A. Mangiarotti, J. Markert, V. Metag, B. Michalska, J. Michel, C. Müntz, L. Naumann, 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, J. Siebenson, Yu. G. Sobolev, S. Spataro, B. Spruck, H. Ströbele, J. Stroth, C. Sturm, A. Tarantola, K. Teilab, P. Tlusty, M. Traxler, R. Trebacz, H. Tsertos, T. Vasiliev, V. Wagner, M. Weber, C. Wendisch, J. Wüstenfeld, S. Yurevich, Y. Zanevsky

We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics measurement of dielectrons radiated from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e+e- invariant mass spectra to elementary p+p data, we observe for e+e- momenta P<0.8 GeV/c a strong modification of the shape of the spectra, which we attribute to an additional rho-like contribution and a decrease in omega yield. These opposite trends are tentatively interpreted as a strong coupling of the rho meson to baryonic resonances and an absorption of the omega meson, which are two aspects of in-medium modification of vector mesons.

View original: http://arxiv.org/abs/1205.1918