A. Balanda

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

Search for e+e− pairs with narrow sum-energy distributions in heavy-ion collisions☆

\ensuremath \pi^{+,0}

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

and

Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

\eta

Experiments on e+e−-line emission in HI collisions

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

A deviation in internal pair conversion

\pi^{+}_{}

High-spin states in 148Eu

and

Associate K^0 production in p+p collisions at 3.5 GeV: The role of Delta(1232)++

\pi^{0}_{}