.
We present transverse momentum spectra, rapidity distribution and multiplicity of
-hyperons measured with the HADES spectrometer in the reaction Ar(1.76AGeV) + KCl . The yield of
is calculated from ...our previously reported
/(
+
) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured
-hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of
, K
+
,
K
0
s
, K
-
,
,
and
. The resulting chemical freeze-out temperature of
T
= (76±2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the different particles.
.
Results on
hyperon production are reported for collisions of p(3.5 GeV) + Nb , studied with the High-Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion ...Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about 90 MeV at a rapidity of
y
= 1.0,
i.e.
slightly below the center-of-mass rapidity for nucleon-nucleon collisions,
. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The
phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions,
i.e.
in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for
production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing
polarization in the weak decay
. Finite negative values of the polarization in the order of 5-20% are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for
p
t
> 300 MeV/c and increases with decreasing rapidity for
y
< 0.8 .
We present the inclusive invariant mass, transverse momentum and rapidity distributions of dielectrons (e
+
e
-
pairs) in p+p interactions at 3.5GeV beam kinetic energy. In the vector meson mass ...region, a distinct peak corresponding to direct ω decays is reconstructed with a 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for e
+
e
-
invariant masses above 0.2 GeV/
c
2
and for transverse pair momenta
p
t
< 1 GeV/
c
, acceptance corrections are, to a large extent, model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross-sections for light vector mesons. Inclusive production cross-sections for π
0
and η mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct η decays into the electron-positron channel is obtained.
.
We report on baryon resonance production and decay in proton-proton collisions at a kinetic energy of 3.5 GeV based on data measured with HADES. The exclusive channels
and
as well as
are studied ...simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon systems were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (
R
with masses < 2 GeV/c
2
. A very good description of the one-pion production is achieved allowing for an estimate of individual baryon resonance production cross sections which are used as input to calculate the dielectron yields from
decays. Two models of the resonance decays into dielectrons are examined assuming a point-like
coupling and the dominance of the
meson. The results of model calculations are compared to data from the exclusive
channel by means of the dielectron and
invariant mass distributions.
We present the inclusive invariant mass, transverse momentum and rapidity distributions of dielectrons (e+e- pairs) in p+p interactions at 3.5GeV beam kinetic energy. In the vector meson mass region, ...a distinct peak corresponding to direct ω decays is reconstructed with a 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for e+e- invariant masses above 0.2 GeV/c 2 and for transverse pair momenta p t < 1 GeV/c, acceptance corrections are, to a large extent, model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross-sections for light vector mesons. Inclusive production cross-sections for π0 and η mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct η decays into the electron-positron channel is obtained.
Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25GeV is investigated. The multi-differential data were measured by the HADES Collaboration. Exclusive channels ...with one pion in the final state (
npπ
+
and
ppπ
0
were put to extended studies based on various observables in the framework of a one-pion exchange model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the
Δ
(1232), yet with a sizable impact of the
N
(1440) and non-resonant partial waves.
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