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arXiv · 2512.12454

Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV

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·F. Hojeij·R. Holzmann·H. Huck·M. Idzik·B. Kämpfer·K-H. Kampert·B. Kardan·V. Kedych·S. Kim·I. Koenig·W. Koenig·M. Kohls·J. Kolas·G. Kornakov·R. Kotte·I. Kres·W. Krueger·A. Kugler·R. Lalik·S. Lebedev·S. Linev·F. Linz·L. Lopes·M. Lorenz·A. Malige·J. Markert·T. Matulewicz·S. Maurus·V. Metag·J. Michel·A. Molenda·C. Müntz·M. Nabroth·L. Naumann·K. Nowakowski·A. Opíchal·J. Orliński·J. -H. Otto·M. Parschau·C. Pauly·D. Pawlowska-Szymanska·V. Pechenov·O. Pechenova·D. Pfeifer·K. Piasecki·J. Pietraszko·T. Povar·K. Prościński·A. Prozorov·W. Przygoda·K. Pysz·B. Ramstein·N. Rathod·J. Ritman·A. Rost·A. Rustamov·P. Salabura·J. Saraiva·K. Scharmann·N. Schild·E. Schwab·F. Scozzi·F. Seck·I. Selyuzhenkov·U. Singh·L. Skorpil·J. Smyrski·S. Spies·A. Sreejith·H. Ströbele·J. Stroth·K. Sumara·O. Svoboda·M. Szala·P. Tlusty
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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 $Λ$ 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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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, F. Hojeij, R. Holzmann, H. Huck, M. Idzik, B. Kämpfer, K-H. Kampert, B. Kardan, V. Kedych, S. Kim, I. Koenig, W. Koenig, M. Kohls, J. Kolas, G. Kornakov, R. Kotte, I. Kres, W. Krueger, A. Kugler, R. Lalik, S. Lebedev, S. Linev, F. Linz, L. Lopes, M. Lorenz, A. Malige, J. Markert, T. Matulewicz, S. Maurus, V. Metag, J. Michel, A. Molenda, C. Müntz, M. Nabroth, L. Naumann, K. Nowakowski, A. Opíchal, J. Orliński, J. -H. Otto, M. Parschau, C. Pauly, D. Pawlowska-Szymanska, V. Pechenov, O. Pechenova, D. Pfeifer, K. Piasecki, J. Pietraszko, T. Povar, K. Prościński, A. Prozorov, W. Przygoda, K. Pysz, B. Ramstein, N. Rathod, J. Ritman, A. Rost, A. Rustamov, P. Salabura, J. Saraiva, K. Scharmann, N. Schild, E. Schwab, F. Scozzi, F. Seck, I. Selyuzhenkov, U. Singh, L. Skorpil, J. Smyrski, S. Spies, A. Sreejith, H. Ströbele, J. Stroth, K. Sumara, O. Svoboda, M. Szala, P. Tlusty. 2025-12-13. Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV. https://doi.org/10.1016/j.physletb.2026.140745

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