The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at sNN=2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon's transverse momentum (pT) and rapidity (yCM) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are 〈PΛ〉(%)=6.8±1.3(stat.)±2.1(syst.) for Au+Au and 〈PΛ〉(%)=6.2±0.4(stat.)±0.6(syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
Abstract The production of $$\Sigma ^{0}$$ Σ 0 hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected ...with the HADES setup. The total production cross section is found to be $${\sigma (pK^{+}\Sigma ^{0}) = 17.7 \pm 1.7 (stat) \pm 1.6 (syst)}$$ σ ( p K + Σ 0 ) = 17.7 ± 1.7 ( s t a t ) ± 1.6 ( s y s t ) µb. Differential cross section distributions of the exclusive channel $${pp \rightarrow pK^{+}\Sigma ^{0}}$$ p p → p K + Σ 0 were analyzed in the center-of-mass, Gottfried–Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to $$\textrm{K}^{+}\Sigma ^{0}$$ K + Σ 0 . The Bonn–Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 $${\textrm{GeV}/\textrm{c}^{2}}$$ GeV / c 2 ( $${\textrm{N}^{*}(1710)}$$ N ∗ ( 1710 ) ) and 1.900 $${\textrm{GeV}/\textrm{c}^{2}}$$ GeV / c 2 ( $${\textrm{N}^{*}(1900)}$$ N ∗ ( 1900 ) or $${\Delta ^{*}(1900)}$$ Δ ∗ ( 1900 ) ) are preferred by the fit.
The production of
Σ
0
hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The ...total production cross section is found to be
σ
(
p
K
+
Σ
0
)
=
17.7
±
1.7
(
s
t
a
t
)
±
1.6
(
s
y
s
t
)
µb. Differential cross section distributions of the exclusive channel
p
p
→
p
K
+
Σ
0
were analyzed in the center-of-mass, Gottfried–Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to
K
+
Σ
0
. The Bonn–Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710
GeV
/
c
2
(
N
∗
(
1710
)
) and 1.900
GeV
/
c
2
(
N
∗
(
1900
)
or
Δ
∗
(
1900
)
) are preferred by the fit.
Inclusive e$^+$e$^-$ production has been studied with HADES in $\pi^-$ + p,
$\pi^-$ + C and $\pi^- + \mathrm{CH}_2$ reactions, using the GSI pion beam at
$\sqrt{s_{\pi p}}$ = 1.49 GeV. Invariant mass ...and transverse momentum
distributions have been measured and reveal contributions from Dalitz decays of
$\pi^0$, $\eta$ mesons and baryon resonances. The transverse momentum
distributions are very sensitive to the underlying kinematics of the various
processes. The baryon contribution exhibits a deviation up to a factor seven
from the QED reference expected for the dielectron decay of a hypothetical
point-like baryon with the production cross section constrained from the
inverse $\gamma$ n$\rightarrow \pi^-$ p reaction. The enhancement is attributed
to a strong four-momentum squared dependence of the time-like electromagnetic
transition form factors as suggested by Vector Meson Dominance (VMD). Two
versions of the VMD, that differ in the photon-baryon coupling, have been
applied in simulations and compared to data. VMD1 (or two-component VMD)
assumes a coupling via the $\rho$ meson and a direct coupling of the photon,
while in VMD2 (or strict VMD) the coupling is only mediated via the $\rho$
meson. The VMD2 model, frequently used in transport calculations for dilepton
decays, is found to overestimate the measured dielectron yields, while a good
description of the data can be obtained with the VMD1 model assuming no phase
difference between the two amplitudes. Similar descriptions have also been
obtained using a time-like baryon transition form factor model where the pion
cloud plays the major role.
Hadron production (\(\pi^\pm\), proton, \(\Lambda\), \(K_S^0\), \(K^\pm\)) in \(\pi^- + \mathrm{C}\) and \(\pi^- + \mathrm{W}\) collisions is investigated at an incident pion beam momentum of ...\(1.7~\mathrm{GeV}/c\). This comprehensive set of data measured with HADES at SIS18/GSI significantly extends the existing world data on hadron production in pion induced reactions and provides a new reference for models that are commonly used for the interpretation of heavy-ion collisions. The measured inclusive differential production cross-sections are compared with state-of-the-art transport model (GiBUU, SMASH) calculations. The (semi-) exclusive channel \(\pi^- + A \rightarrow \Lambda + K_S^0 +X\), in which the kinematics of the strange hadrons are correlated, is also investigated and compared to a model calculation. Agreement and remaining tensions between data and the current version of the considered transport models are discussed.
The production of $\Sigma^0$ hyperons in proton proton collisions at a beam
kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was
investigated using data collected with the HADES setup. ...The total production
cross section is found to be $\mathrm{\sigma (pK^{+}\Sigma^{0}) \mu b = 17.7
\pm 1.7 (stat) \pm 1.6 (syst)}$. Differential cross section distributions of
the exclusive channel $\mathrm{pp \rightarrow pK^{+}\Sigma^{0}}$ were analyzed
in the center-of-mass, Gottfried-Jackson and helicity reference frames for the
first time at the excess energy of 556 MeV. The data support the interplay
between pion and kaon exchange mechanisms and clearly demonstrate the
contribution of interfering nucleon resonances decaying to
$\mathrm{K^{+}\Sigma^{0}}$. The Bonn-Gatchina partial wave analysis was
employed to analyse the data. Due to the limited statistics, it was not
possible to obtain an unambiguous determination of the relative contribution of
intermediate nucleon resonances to the final state. However nucleon resonances
with masses around 1.710 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1710)}$) and
1.900 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1900)}$ or
$\mathrm{\Delta^{*}(1900)}$) are preferred by the fit.
The global polarization of {\Lambda} hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are <P_{\Lambda}>(%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and <P_{\Lambda}>(%) = 6.2 \pm 0.4 (stat.) \pm 0.6 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
The production of \(\Sigma^0\) hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES ...setup. The total production cross section is found to be \(\mathrm{\sigma (pK^{+}\Sigma^{0}) \mu b = 17.7 \pm 1.7 (stat) \pm 1.6 (syst)}\). Differential cross section distributions of the exclusive channel \(\mathrm{pp \rightarrow pK^{+}\Sigma^{0}}\) were analyzed in the center-of-mass, Gottfried-Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to \(\mathrm{K^{+}\Sigma^{0}}\). The Bonn-Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 \(\mathrm{GeV/c^{2}}\) (\(\mathrm{N^{*}(1710)}\)) and 1.900 \(\mathrm{GeV/c^{2}}\) (\(\mathrm{N^{*}(1900)}\) or \(\mathrm{\Delta^{*}(1900)}\)) are preferred by the fit.
Basic physical characteristics of electromagnetic fields and their influence on living organisms were reported. Standard values of electromagnetic field intensity, according to obligatory ...recommendations for the cow shed buildings, were given. Electric and magnetic field intensities were measured in four cow sheds in the north-eastern Poland. Measured values of electromagnetic fields in tested livestock buildings were much less than the standard values both, on working stands for the people and in the livestock stalls. The highest measured value of magnetic field intensity achieved 3.1 A/m (at acceptable standard 80 A/m); the intensity of electric fields was negligible
Effect of "geopathic" radiation emitted by water underflows was evaluated in a cow-shed localized in Zulawy region. On a ten-degree scale, the teams of dowsers identified 4 zones of underflow ...activity, including 3 extremely harmful areas: 10, 9 and 5 deg, and control zone of 1 deg. Milk yields, fat production and herd replacement were analysed. The lowest milk and fat yields were obtained from cows staying on stands subjected to 10 and 9 deg radiation; the highest - at 1 deg radiation. The highest herd replacement rate was recorded for cows receiving 10 and 9 deg radiation. Cows were removed from the herd due to infertility, leukaemia, miscarriages, post-calving palsy, circulatory failure and low milk yield
