Investigating hadronic resonances in pp interactions with HADES

¹ Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-348 Kraków, Poland
² GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany
³ Institute of Physics, Slovak Academy of Sciences, 84228 Bratislava, Slovakia
⁴ LIP-Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516 Coimbra, Portugal
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 E12, 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 (UMR 8608), CNRS/IN2P3 - Université Paris Sud, F-91406 Orsay Cedex, France
¹⁶ Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068 Rez, Czech Republic
¹⁷ LabCAF. F. Física, Univ. de Santiago de Compostela, 15706 Santiago de Compostela, Spain
^a also at ISEC Coimbra, Coimbra, Portugal
^b also at ExtreMe Matter Institute EMMI, 64291 Darmstadt, Germany
^c also at Technische Universität Dresden, 01062 Dresden, Germany
^d also at Frederick University, 1036 Nicosia, Cyprus
^e also at Dipartimento di Fisica and INFN, Università di Torino, 10125 Torino, Italy
^f also at Utrecht University, 3584 CC Utrecht, The Netherlands

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

Published online: 22 June 2015

Abstract

In this paper we report on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV and 3.5 GeV, based on data measured with HADES. Exclusive channels npπ⁺ and ppπ⁰ as well as ppe⁺e⁻ were studied simultaneously in the framework of a one-boson exchange model. The resonance cross sections were determined from the one-pion channels for Δ(1232) and N(1440) (1.25 GeV) as well as further Δ and N* resonances up to 2 GeV/c² for the 3.5 GeV data. The data at 1.25 GeV energy were also analysed within the framework of the partial wave analysis together with the set of several other measurements at lower energies. The obtained solutions provided the evolution of resonance production with the beam energy, showing a sizeable non-resonant contribution but with still dominating contribution of Δ(1232)P₃₃. In the case of 3.5 GeV data, the study of the ppe⁺e⁻ channel gave the insight on the Dalitz decays of the baryon resonances and, in particular, on the electromagnetic transition form-factors in the time-like region. We show that the assumption of a constant electromagnetic transition form-factors leads to underestimation of the yield in the dielectron invariant mass spectrum below the vector mesons pole. On the other hand, a comparison with various transport models shows the important role of intermediate ρ production, though with a large model dependency. The exclusive channels analysis done by the HADES collaboration provides new stringent restrictions on the parameterizations used in the models.