Analysis of the exclusive final state npe+e- in the 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 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of e+e- pairs above the π0 mass in the exclusive channel dp → 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- Δ excitation combined with intermediate ρ-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 sides.
- Publication:
-
European Physical Journal A
- Pub Date:
- July 2017
- DOI:
- 10.1140/epja/i2017-12341-3
- arXiv:
- arXiv:1703.08575
- Bibcode:
- 2017EPJA...53..149A
- Keywords:
-
- Nuclear Experiment;
- J.2
- E-Print:
- 12 pages, 7 figures