Analysis of the exclusive final state npe+e- in the quasi-free np reaction

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. 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; D. M. Mihaylov; E. Morinière; S. Morozov; C. Müntz; R. Münzer; L. Naumann; K. Nowakowski; M. Palka; Y. Parpottas; V. Pechenov; O. Pechenova; V. Petousis; 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; S. Spataro; H. Ströbele; J. Stroth; P. Strzempek; C. Sturm; O. Svoboda; P. Tlusty; M. Traxler; H. Tsertos; E. Usenko; V. Wagner; C. Wendisch; M. G. Wiebusch; J. Wirth; Y. Zanevsky; P. Zumbruch; A. V. Sarantsev

doi:10.1140/epja/i2017-12341-3

2022 Impact factor 2.7

Hadrons and Nuclei

Open Access

Eur. Phys. J. A (2017) 53: 149
https://doi.org/10.1140/epja/i2017-12341-3

Regular Article - Experimental Physics

Analysis of the exclusive final state npe⁺e^- in the quasi-free np reaction

HADES Collaboration
J. Adamczewski-Musch⁴, O. Arnold¹⁰^,9, E. T. Atomssa¹⁵, C. Behnke⁸, A. Belounnas¹⁵, A. Belyaev⁷, J. C. Berger-Chen¹⁰^,9, J. Biernat³, A. Blanco², C. Blume⁸, M. Böhmer¹⁰, P. Bordalo², S. Chernenko⁷, L. Chlad¹⁶, C. Deveaux¹¹, J. Dreyer⁶, A. Dybczak³, E. Epple¹⁰^,9, L. Fabbietti¹⁰^,9, O. Fateev⁷, P. Filip¹, P. Fonte², C. Franco², J. Friese¹⁰, I. Fröhlich⁸, T. Galatyuk⁵^,4, J. A. Garzón¹⁷, R. Gernhäuser¹⁰, M. Golubeva¹², F. Guber¹², M. Gumberidze⁵, S. Harabasz⁵^,3, T. Heinz⁴, T. Hennino¹⁵, S. Hlavac¹, C. Höhne¹¹, R. Holzmann⁴, A. Ierusalimov⁷, A. Ivashkin¹², B. Kämpfer⁶, T. Karavicheva¹², B. Kardan⁸, I. Koenig⁴, W. Koenig⁴, B. W. Kolb⁴, G. Korcyl³, G. Kornakov⁵, R. Kotte⁶, W. Kühn¹¹, A. Kugler¹⁶, T. Kunz¹⁰, A. Kurepin¹², A. Kurilkin⁷, P. Kurilkin⁷, V. Ladygin⁷, R. Lalik¹⁰^,9, K. Lapidus¹⁰^,9, A. Lebedev¹³, T. Liu¹⁵, L. Lopes², M. Lorenz⁸, T. Mahmoud¹¹, L. Maier¹⁰, A. Mangiarotti², J. Markert⁴, S. Maurus¹⁰, V. Metag¹¹, J. Michel⁸, D. M. Mihaylov¹⁰^,9, E. Morinière¹⁵, S. Morozov¹², C. Müntz⁸, R. Münzer¹⁰^,9, L. Naumann⁶, K. Nowakowski³, M. Palka³, Y. Parpottas¹⁴, V. Pechenov⁴, O. Pechenova⁸, V. Petousis¹⁴, O. Petukhov¹², J. Pietraszko⁴, W. Przygoda³^*, S. Ramos², B. Ramstein¹⁵, A. Reshetin¹², P. Rodriguez-Ramos¹⁶, P. Rosier¹⁵, A. Rost⁵, A. Sadovsky¹², P. Salabura³, T. Scheib⁸, H. Schuldes⁸, E. Schwab⁴, F. Scozzi⁵^,15, F. Seck⁵, P. Sellheim⁸, J. Siebenson¹⁰, L. Silva², Yu. G. Sobolev¹⁶, S. Spataro¹, H. Ströbele⁸, J. Stroth⁸^,4, P. Strzempek³, C. Sturm⁴, O. Svoboda¹⁶, P. Tlusty¹⁶, M. Traxler⁴, H. Tsertos¹⁴, E. Usenko¹², V. Wagner¹⁶, C. Wendisch⁴, M. G. Wiebusch⁸, J. Wirth¹⁰^,9, Y. Zanevsky⁷, P. Zumbruch⁴ and A. V. Sarantsev¹⁸

¹ Institute of Physics, Slovak Academy of Sciences, 84228, Bratislava, Slovakia
² LIP-Laboratório de Instrumentação e Fısica Experimental de Partıculas, 3004-516, Coimbra, Portugal
³ Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059, Kraków, Poland
⁴ GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
⁵ Technische Universität Darmstadt, 64289, Darmstadt, Germany
⁶ Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, 01314, Dresden, Germany
⁷ Joint Institute of Nuclear Research, 141980, Dubna, Russia
⁸ Institut für Kernphysik, Goethe-Universität, 60438, Frankfurt, Germany
⁹ Excellence Cluster “Origin and Structure of the Universe”, 85748, Garching, Germany
¹⁰ Physik Department E62, Technische Universität München, 85748, Garching, Germany
¹¹ II. Physikalisches Institut, Justus Liebig Universität Giessen, 35392, Giessen, Germany
¹² Institute for Nuclear Research, Russian Academy of Science, 117312, Moscow, Russia
¹³ Institute of Theoretical and Experimental Physics, 117218, Moscow, Russia
¹⁴ Department of Physics, University of Cyprus, 1678, Nicosia, Cyprus
¹⁵ Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, F-91406, Orsay Cedex, France
¹⁶ Nuclear Physics Institute, The Czech Academy of Sciences, 25068, Rez, Czech Republic
¹⁷ LabCAF. F. Fısica, Univ. de Santiago de Compostela, 15706, Santiago de Compostela, Spain
¹⁸ NRC “Kurchatov Institute”, PNPI, 188300, Gatchina, Russia

^* e-mail: witold.przygoda@uj.edu.pl

Received: 24 March 2017
Accepted: 13 June 2017
Published online: 18 July 2017

Abstract

We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of pairs above the mass in the exclusive channel as compared to the exclusive channel 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- excitation combined with intermediate -meson production. Differential cross sections as a function of the 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 sides.