Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV
Authors:
R. Abou Yassine,
J. Adamczewski-Musch,
C. Asal,
M. Becker,
A. Belounnas,
A. Blanco,
C. Blume,
L. Chlad,
P. Chudoba,
I. Ciepał,
J. Dreyer,
W. A. Esmail,
L. Fabbietti,
H. Floersheimer,
J. Förtsch,
P. Fonte,
J. Friese,
I. Fröhlich,
T. Galatyuk,
R. Greifenhagen,
M. Grunwald,
M. Gumberidze,
S. Harabasz,
T. Heinz,
C. Höhne
, et al. (89 additional authors not shown)
Abstract:
We present the first observation of $\mathrm{^{3}_ΛH}$ and $\mathrm{^{4}_ΛH}$ in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV, emitted around mid-rapidity. The hypernuclei are reconstructed via their two-body decay channels and identified through their weak-decay topology, employing an artificial neural network for enhanced discrimination. The analysis methodology is validated using…
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We present the first observation of $\mathrm{^{3}_ΛH}$ and $\mathrm{^{4}_ΛH}$ in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV, emitted around mid-rapidity. The hypernuclei are reconstructed via their two-body decay channels and identified through their weak-decay topology, employing an artificial neural network for enhanced discrimination. The analysis methodology is validated using $Λ$ hyperons. The resulting rapidity distributions, dN/dy, exhibit a bell shape centered at mid-rapidity. The yield of $\mathrm{^{4}_ΛH}$ is equal to or exceeds that of $\mathrm{^{3}_ΛH}$, which contrasts the measurement from the STAR collaboration at $\mathrm{\sqrt{s_{NN}}}$ = 3 GeV and is consistent with a scenario in which hypernuclei receive feed-down from excited states. The data enable a high-precision measurement of the hypernuclei lifetimes. For the $\mathrm{^{3}_ΛH}$, a lifetime of $\mathrm{τ_{^{3}_ΛH}}$ = $(239 \pm 23{\mathrm{(stat)}} \pm 18{\mathrm{(sys)}})\,\mathrm{ps}$, is extracted, consistent on the 1$σ$ level with that of the free $Λ$. In contrast, the $\mathrm{^{4}_ΛH}$ lifetime of $\mathrm{τ_{^{4}_ΛH}}$ = $(209 \pm 7{\mathrm{(stat)}} \pm 10{\mathrm{(sys)}})\,\mathrm{ps}$, shows a 4.5 $σ$ deviation from the free $Λ$ lifetime. The results consolidate the available world data.
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Submitted 13 December, 2025;
originally announced December 2025.
Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions
Authors:
R. Abou Yassine,
J. Adamczewski-Musch,
C. Asal,
M. Becker,
A. Belounnas,
A. Blanco,
C. Blume,
L. Chlad,
P. Chudoba,
I. Ciepal,
M. Cordts,
J. Dreyer,
W. A. Esmail,
L. Fabbietti,
H. Floersheimer,
P. Fonte,
J. Friese,
I. Fröhlich,
J. Förtsch,
T. Galatyuk,
T Gniazdowski,
R. Greifenhagen,
M. Grunwald,
M. Gumberidze,
S. Harabasz
, et al. (83 additional authors not shown)
Abstract:
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 \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…
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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 \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_Λ>(%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and <P_Λ>(%) = 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.
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Submitted 28 October, 2022; v1 submitted 11 July, 2022;
originally announced July 2022.