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.
.
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.
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.
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.
Results on the production of the double-strange cascade hyperon \(\mathrm{\Xi^-}\) 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. For the first time, subthreshold \(\mathrm{\Xi^-}\) production is observed in proton-nucleus interactions. Assuming a \(\mathrm{\Xi^-}\) phase-space distribution similar to that of \(\mathrm{\Lambda}\) hyperons, the production probability amounts to \(P_{\mathrm{\Xi^-}}=(2.0\,\pm0.4\,\mathrm{(stat)}\,\pm 0.3\,\mathrm{(norm)}\,\pm 0.6\,\mathrm{(syst)})\times10^{-4}\) resulting in a \(\mathrm{\Xi^-/(\Lambda+\Sigma^0)}\) ratio of \(P_{\mathrm{\Xi^-}}/\ P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm 0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}\). Available model predictions are significantly lower than the estimated \(\mathrm{\Xi^-}\) yield.
Results on \(\Lambda\) 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, \(y_{cm}=1.12\). The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The \(\Lambda\) 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 \(\Lambda\) 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 \(\Lambda\) polarization in the weak decay \(\Lambda\rightarrow p \pi^-\). 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 \(y < 0.8\).
PDF
