The Dalitz decay of baryonic resonances (B
→
N
e
+
e
-
) gives access to the time-like electromagnetic structure of baryonic transitions at small positive values of the squared four momentum ...transferred. Such processes were investigated by the HADES collaboration in elementary hadronic interactions. The Dalitz decay branching ratio of the
Δ
(
1232
)
resonance has been measured for the first time in pp reactions at 1.25 GeV beam energy. At higher energies, the
e
+
e
-
emission from baryonic decays is shown to be sensitive to transition form factors of the Vector Dominance Model type. Using a pion beam, Dalitz decays of baryonic resonances can be measured more directly. In addition, the simultaneous measurement of hadronic channels provides a new data base for baryon spectroscopy issues. Preliminary results of a test experiment in the N(1520) region are shown, together with prospects for higher resonance studies. A project of measuring hyperon Dalitz decays at GSI and later on at FAIR is also discussed. The study of Dalitz decays of baryon resonances and, in particular, the role of the
ρ
meson brings useful constraints for the study of medium effects also investigated by the HADES collaboration in reactions with nuclei.
Tests of optical glues for the PANDA electromagnetic calorimeter Dbeyssi, A.; Tomasi-Gustafsson, E.; Hennino, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2013, Volume:
722
Journal Article
Peer reviewed
This paper reports on the results of tests for low temperature applications of two commercial optical glues in the electromagnetic calorimeter of PANDA at FAIR. Mechanical, thermal and optical ...properties are presented, as well as radiation hardness to photon and proton radiation.
Design of the pluto event generator Fröhlich, I; Galatyuk, T; Holzmann, R ...
Journal of physics. Conference series,
04/2010, Volume:
219, Issue:
3
Journal Article
Peer reviewed
Open access
We present the design of the simulation package Pluto, aimed at the study of hadronic interactions at SIS and FAIR energies. Its main mission is to offer a modular framework with an object-oriented ...structure, thereby making additions such as new particles, decays of resonances, new models up to modules for entire changes easily applicable. Overall consistency is ensured by a plugin- and distribution manager. Particular features are the support of a modular structure for physics process descriptions, and the possibility to access the particle stream for on-line modifications. Additional configuration and self-made classes can be attached by the user without re-compiling the package, which makes Pluto extremely configurable.
Flow coefficients vn of the orders n = 1 – 6 are measured with the High-Acceptance Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, ...and rapidity in Au + Au collisions at √sNN = 2.4 GeV. Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.
We present a search for the e+e− decay of a hypothetical dark photon, also named U vector boson, in inclusive dielectron spectra measured by HADES in the p(3.5 GeV) + p, Nb reactions, as well as the ...Ar (1.756 GeV/u) + KCl reaction. An upper limit on the kinetic mixing parameter squared ϵ2 at 90% CL has been obtained for the mass range MU=0.02–0.55 GeV/c2 and is compared with the present world data set. For masses 0.03–0.1 GeV/c2, the limit has been lowered with respect to previous results, allowing now to exclude a large part of the parameter region favored by the muon g−2 anomaly. Furthermore, an improved upper limit on the branching ratio of 2.3×10−6 has been set on the helicity-suppressed direct decay of the eta meson, η→e+e−, at 90% CL.
High-precision measurements of flow coefficients
v
n
(
n
=
1
-
4
) for protons, deuterons and tritons relative to the first-order spectator plane have been performed in Au+Au collisions at
s
NN
=
2.4
... GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at the SIS18/GSI. Flow coefficients are studied as a function of transverse momentum
p
t
and rapidity
y
cm
over a large region of phase-space and for several classes of collision centrality. A clear mass hierarchy, as expected by relativistic hydrodynamics, is found for the slope of
v
1
,
d
v
1
/
d
y
′
|
y
′
=
0
where
y
′
is the scaled rapidity, and for
v
2
at mid-rapidity. Scaling with the number of nucleons is observed for the
p
t
dependence of
v
2
and
v
4
at mid-rapidity, which is indicative for nuclear coalescence as the main process responsible for light nuclei formation.
v
2
is found to scale with the initial eccentricity
⟨
ϵ
2
⟩
, while
v
4
scales with
⟨
ϵ
2
⟩
2
and
⟨
ϵ
4
⟩
. The multi-differential high-precision data on
v
1
,
v
2
,
v
3
, and
v
4
provides important constraints on the equation-of-state of compressed baryonic matter.
The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the \PANDA detector is discussed. Detailed simulations on signal efficiency for the ...annihilation of $\bar p +p $ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $\bar p +p \to e^++ e^-$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2\simeq 14$ (GeV/c)$^2$. The total $\bar p +p\to e^++e^-$ cross section will be measured up to $q^2\simeq 28$ (GeV/c)$^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated.
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