Abstract
We present the results of two-pion production in tagged quasi-free np collisions at a deutron incident beam energy of 1.25 GeV/c measured with the High-Acceptance Di-Electron Spectrometer (HADES) installed at GSI. The specific acceptance of HADES allowed for the first time to obtain high-precision data on π+π− and π−π0 production in np collisions in a region corresponding to large transverse momenta of the secondary particles. The obtained differential cross section data provide strong constraints on the production mechanisms and on the various baryon resonance contributions (∆∆, N(1440), N(1520), ∆(1600)). The invariant mass and angular distributions from the np → npπ+π −and np → ppπ−π0 reactions are compared with different theoretical model predictions.
Highlights
The two-pion production in nucleon-nucleon (NN) collisions is a very rich source of information about the baryon excitation spectrum and the baryon-baryon interaction properties
In this work we present high statistics invariant mass and angular distributions on π+π− and π−π0 production in quasi-free np collisions at an incident deutron beam energy of 1.25 GeV/c obtained with the High-Acceptance Di-Electron Spectrometer (HADES) spectrometer
The calculations [3] and [12] predict that the ππ production for the np → npπ+π− reaction at 1.25 GeV is mainly caused by the ΔΔ excitation, while according to the OPER model [11] the ΔΔ and OBE gives commensurable contributions
Summary
The two-pion production in nucleon-nucleon (NN) collisions is a very rich source of information about the baryon excitation spectrum and the baryon-baryon interaction properties. In this work we present high statistics invariant mass and angular distributions on π+π− and π−π0 production in quasi-free np collisions at an incident deutron beam energy of 1.25 GeV/c obtained with the HADES spectrometer. The experimental data have been obtained using the High Acceptance Di-Electron Spectrometer (HADES) [9] located at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany.
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