arXiv · 1703.08575
Analysis of the exclusive final state npe$^+$e$^-$ in quasi-free np reaction
Abstract
We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25 GeV/u inpinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of $e^+e^-$ pairs above the $\pi^{0}$ mass in the exclusive channel $dp \to npe^{+}e^{-}(p_{spect})$ as compared to the exclusive channel $ppe^{+}e^{-}$ measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double-$\Delta$ excitation combined with intermediate $\rho$-meson production. Differential cross sections as a function of the $e^+e^-$ invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical side.
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J. Adamczewski-Musch, O. Arnold, E. T. Atomssa, C. Behnke, A. Belounnas, A. Belyaev, J. C. Berger-Chen, J. Biernat, A. Blanco, C. Blume, M. Böhmer, P. Bordalo, S. Chernenko, L. Chlad, C. Deveaux, J. Dreyer, A. Dybczak, E. Epple, L. Fabbietti, O. Fateev, P. Filip, P. Finocchiaro, P. Fonte, C. Franco, J. Friese, I. Fröhlich, T. Galatyuk, J. A. Garzón, R. Gernhäuser, M. Golubeva, F. Guber, M. Gumberidze, S. Harabasz, T. Heinz, T. Hennino, S. Hlavac, C. Höhne, R. Holzmann, A. Ierusalimov, A. Ivashkin, B. Kämpfer, T. Karavicheva, B. Kardan, I. Koenig, W. Koenig, B. W. Kolb, G. Korcyl, G. Kornakov, R. Kotte, W. Kühn, A. Kugler, T. Kunz, A. Kurepin, A. Kurilkin, P. Kurilkin, V. Ladygin, R. Lalik, K. Lapidus, A. Lebedev, T. Liu, L. Lopes, M. Lorenz, T. Mahmoud, L. Maier, A. Mangiarotti, J. Markert, S. Maurus, V. Metag, J. Michel, E. Morinière, D. M. Mihaylov, S. Morozov, C. Müntz, R. Münzer, L. Naumann, K. N. Nowakowski, M. Palka, Y. Parpottas, V. Pechenov, O. Pechenova, O. Petukhov, J. Pietraszko, W. Przygoda, S. Ramos, B. Ramstein, A. Reshetin, P. Rodriguez-Ramos, P. Rosier, A. Rost, A. Sadovsky, P. Salabura, T. Scheib, H. Schuldes, E. Schwab, F. Scozzi, F. Seck, P. Sellheim, J. Siebenson, L. Silva, Yu. G. Sobolev. 2017-03-24. Analysis of the exclusive final state npe$^+$e$^-$ in quasi-free np reaction. https://doi.org/10.1140/epja/i2017-12341-3
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