The GEp-III and GEp-2γ experiments, carried out in Jefferson Lab’s Hall C from 2007–2008, consisted of measurements of polarization transfer in elastic electron–proton scattering at momentum ...transfers of Q2=2.5,5.2,6.8, and 8.54 GeV 2. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio R=μpGEp∕GMp at large values of Q2 and to search for effects beyond the Born approximation in polarization transfer observables at Q2=2.5GeV2. The final results of both experiments were reported in a recent archival publication. A full reanalysis of the data from both experiments was carried out in order to reduce the systematic and, for the GEp-2γ experiment, statistical uncertainties. This technical note provides additional details of the final analysis omitted from the main publication, including the final evaluation of the systematic uncertainties.
We present first data on sub-threshold production of Ks0 mesons and Λ hyperons in Au+Au collisions at sNN=2.4 GeV. We observe an universal 〈Apart〉 scaling of hadrons containing strangeness, ...independent of their corresponding production thresholds. Comparing the yields, their 〈Apart〉 scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of them can simultaneously describe these observables with reasonable χ2 values.
Here, this technical note provides supplemental material for the archival publication of the measure- ments of polarization transfer observables in elastic e→p → e→p scattering from the GEp-III and ...GEp-2γ experiments in Jefferson Lab's Hall C.
We present and discuss recent experimental activities of the HADES collaboration on open and hidden strangeness production close or below the elementary NN threshold. Special emphasis is put on the ...feed-down from φ mesons to antikaons, the presence of the Ξ- excess in cold nuclear matter and the comparison of statistical model rates to elementary p+p data. The implications for the interpretation of heavy-ion data are discussed as well.
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.
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 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.
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