Deep sub-threshold $\phi$ production in Au+Au collisions

The HADES collaboration Adamczewski-Musch, J. ; Arnold, O. ; Behnke, C. ; et al.
Phys.Lett. B778 (2018) 403-407, 2018.
Inspire Record 1519164 DOI 10.17182/hepdata.92099

We present data on charged kaons (K+-) and {\phi} mesons in Au(1.23A GeV)+Au collisions. It is the first simultaneous measurement of K and {\phi} mesons in central heavy-ion collisions below a kinetic beam energy of 10A GeV. The {\phi}/K- multiplicity ratio is found to be surprisingly high with a value of 0.52 +- 0.16 and shows no dependence on the centrality of the collision. Consequently, the different slopes of the K+ and K- transverse-mass spectra can be explained solely by feed- down, which substantially softens the spectra of K- mesons. Hence, in contrast to the commonly adapted argumentation in literature, the different slopes do not necessarily imply diverging freeze- out temperatures of K+ and K- mesons caused by different couplings to baryons.

12 data tables

Acceptance and efficiency corrected transverse-mass spectra around mid-rapidity.

$K^{+}$ signal and the corresponding background fit for the region covering mid-rapidity and $m_{t}−m_{0}$ between 25 and 50 $MeV/c^{2}$.

$K^{-}$ signal and the corresponding background fit for the region covering mid-rapidity and $m_{t}−m_{0}$ between 50 and 75 $MeV/c^{2}$.

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Version 2
Probing dense baryon-rich matter with virtual photons

The HADES collaboration Adamczewski-Musch, J. ; Arnold, O. ; Behnke, C. ; et al.
Nature Phys. 15 (2019) 1040-1045, 2019.
Inspire Record 1758156 DOI 10.17182/hepdata.90846

About 10 μs after the Big Bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at temperatures close to kT = 150 MeV and densities several times higher than those found in nuclei. This quantum chromodynamics (QCD) matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. The different phases in which QCD matter may exist depend for example on temperature, pressure or baryochemical potential, and can be probed by studying the emission of electromagnetic radiation. Electron–positron pairs emerge from the decay of virtual photons, which immediately decouple from the strong interaction, and thus provide information about the properties of QCD matter at various stages. Here, we report the observation of virtual photon emission from baryon-rich QCD matter. The spectral distribution of the electron–positron pairs is nearly exponential, providing evidence for a source of temperature in excess of 70 MeV with constituents whose properties have been modified, thus reflecting peculiarities of strong-interaction QCD matter. Its bulk properties are similar to the dense matter formed in the final state of a neutron star merger, as apparent from recent multimessenger observation.

10 data tables

Reconstructed $e^{+} e^{-}$ mass distribution from Au+Au collisions.

Reconstructed $e^{+} e^{-}$ mass distribution from Au+Au collisions.

Reconstructed $e^{+} e^{-}$ mass distribution from Au+Au collisions.

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Sub-threshold production of K$^{0}_{s}$ mesons and ${\Lambda}$ hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV

The HADES collaboration Adamczewski-Musch, J. ; Arnold, O. ; Behnke, C. ; et al.
Phys.Lett. B793 (2019) 457-463, 2019.
Inspire Record 1709767 DOI 10.17182/hepdata.90954

We present first data on sub-threshold production of K0 s mesons and {\Lambda} hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 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 the latter can simultaneously describe all observables with reasonable \c{hi}2 values.

18 data tables

Example of $K^{0}_{S}$ signal for 0-40% most central events, over mixed-event background for the bin $-0.05 < y_{cm} < 0.05$ and reduced transverse masses between $80-120 MeV/c^{2}$.

Example of $\Lambda$ signal for 0-40% most central events, over mixed-event background for the bin $-0.05 < y_{cm} < 0.05$ and reduced transverse masses between $100-150 MeV/c^{2}$.

$K^{0}_{S}$ and $\Lambda$ multiplicities in full phase space and inverse slopes at mid-rapidity $T_{Eff}$ for a given centrality.

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