.
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.
Abstract
We present high-statistic data on charged-pion emission from Au + Au collisions at
$$\sqrt{s_{\mathrm{NN}}} = 2.4~\hbox {GeV}$$
s
NN
=
2.4
GeV
(corresponding to
$$E_{beam} = 1.23~\hbox {A ...GeV}$$
E
beam
=
1.23
A GeV
) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nucleon decreases moderately with increasing centrality. The polar angular distributions are found to be non-isotropic even for the most central event class. Our results on pion multiplicity fit well into the general trend of the available world data, but undershoot by
$$2.5~\sigma $$
2.5
σ
data from the FOPI experiment measured at slightly lower beam energy. We compare our data to state-of-the-art transport model calculations (PHSD, IQMD, PHQMD, GiBUU and SMASH) and find substantial differences between the measurement and the results of these calculations.
The reaction p(@3.5 GeV)+p→p+Λ+K+ can be studied to search for the existence of kaonic bound states like ppK− leading to this final state. This effort has been motivated by the assumption that in p+p ...collisions the Λ(1405) resonance can act as a doorway to the formation of the kaonic bound states. The status of this analysis within the HADES Collaboration, with particular emphasis on the comparison to simulations, is shown in this work and the deviation method utilized by the DISTO Collaboration in a similar analysis is discussed. The outcome suggests the employment of a partial wave analysis do disentangle the different contributions to the measured pK+Λ final state.
.
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 .
At energies below sNN≈2.55GeV, strange quarks cannot be produced in binary nucleon-nucleon collisions because of the higher production threshold of the lightest hadrons carrying strangeness. Hence, ...the investigation of sub-threshold strangeness production in heavy-ion collisions is one of the most promising probes, to access the properties of the created system, as the missing energy must be provided by the latter one. For the first time, a nearly complete set of strange particles has been reconstructed in the 40% most central Au+Au collisions at sNN=2.42GeV. The data sample includes multi-differential representations of charged and neutral particles containing strangeness (K±, Ks0, ϕ, Λ). To achieve a better understanding of strangeness production the properties of the short-lived resonances have to be investigated. The first steps in this direction are presented here, including the reconstruction of baryon resonances using a new iterative technique, comparison to microscopic transport model calculations and interpretation of the pion transverse momentum distribution.
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.
The production of Σ0 baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to sNN=3.18 GeV) is studied with the detector set-up HADES at GSI, Darmstadt. Σ0s were identified via the decay ...Σ0→Λγ with subsequent decays Λ→pπ− in coincidence with a e+e− pair from either external (γ→e+e−) or internal (Dalitz decay γ⁎→e+e−) gamma conversions. The differential Σ0 cross section integrated over the detector acceptance, i.e. the rapidity interval 0.5<y<1.1, has been extracted as ΔσΣ0=2.3±(0.2)stat±(−0.6+0.6)sys±(0.2)norm mb, yielding the inclusive production cross section in full phase space σΣ0total=5.8±(0.5)stat±(−1.4+1.4)sys±(0.6)norm±(1.7)extrapol mb by averaging over different extrapolation methods. The Λall/Σ0 ratio within the HADES acceptance is equal to 2.3±(0.2)stat±(−0.6+0.6)sys. The obtained rapidity and momentum distributions are compared to transport model calculations. The Σ0 yield agrees with the statistical model of particle production in nuclear reactions.
.
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.
Abstract
High-statistics
$$\pi ^-\pi ^-$$
π
-
π
-
and
$$\pi ^+\pi ^+$$
π
+
π
+
femtoscopy data are presented for Au + Au collisions at
$$\sqrt{s_\mathrm{NN}} = 2.4~\hbox {GeV}$$
s
NN
=
2.4
GeV
, ...measured with HADES at SIS18/GSI. The experimental correlation functions allow the determination of the space-time extent of the corresponding emission sources via a comparison to models. The emission source, parametrized as three-dimensional Gaussian distribution, is studied in dependence on pair transverse momentum, azimuthal emission angle with respect to the reaction plane, collision centrality and beam energy. For all centralities and transverse momenta, a geometrical distribution of ellipsoidal shape is found in the plane perpendicular to the beam direction with the larger extension perpendicular to the reaction plane. For large transverse momenta, the corresponding eccentricity approaches the initial eccentricity. The eccentricity is smallest for most central collisions, where the shape is almost circular. The magnitude of the tilt angle of the emission ellipsoid in the reaction plane decreases with increasing centrality and increasing transverse momentum. All source radii increase with centrality, largely exhibiting a linear rise with the cube root of the number of participants. A substantial charge-sign difference of the source radii is found, appearing most pronounced at low transverse momentum. The extracted source parameters are consistent with the extrapolation of their energy dependence down from higher energies.
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