F. Dohrmann

Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

Abstract We report measurements of electron pair production in elementary p + p and d + p reactions at 1.25 GeV / u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n + p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass M e + e − > 0.15 GeV / c 2 is about an order of magnitude larger in n + p reactions as compared to p + p . A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C + C reactions are compatible with a superposition of elementary n + p and p + p collisions, leaving little room for additional electron pair sources in such light collision systems.

Dielectron production in Ar+KCl collisions at 1.76A GeV

We present results on dielectron production in 40 Ar+KCl collisions at 1.76A GeV. For the first time ω mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The ω multiplicity has been extracted and compared to the yields of other particles, in particular of the φ meson. At intermediate e + e invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for ]

Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES

Abstract.We present measurements of exclusive

Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy

\ensuremath \pi^{+,0}

A versatile method for simulating pp \rightarrow ppe+e- and dp \rightarrow pne+e-pspec reactions

and

A versatile method for simulating pp → ppe + e − and dp → pne + e − p spec reactions

\eta

Electroproduction of kaons on light nuclei

production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of

A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions

\pi^{+}_{}

QuasifreeΛ,Σ0, andΣ−electroproduction fromH1,2,He3,4, and carbon

and

Quasifree Lambda, Sigma^0, and Sigma^- electroproduction from 1,2H, 3,4He, and Carbon

\pi^{0}_{}