engYassine, R. AbouAdamczewski-Musch, J.Dreyer, J.Traxler, M.Treliński, S.Udrea, I. C.Ulrich-Pur, F.Ungethum, C.Wagner, V.Weber, A. A.Wendisch, C.Wirth, J.Władyszewska, A.Esmail, Waleed Ahmed MohammedZbroszczyk, H. P.Zherebtsova, E.Zieliński, M.Zumbruch, P.HADES CollaborationFabbietti, L.Floersheimer, H.Förtsch, J.Fonte, P.Friese, J.Fröhlich, I.Galatyuk, T.Greifenhagen, R.Asal, C.Grunwald, M.Gumberidze, M.Harabasz, S.Heinz, T.Höhne, C.Hojeij, F.Holzmann, RomainHuck, H.Idzik, M.Kämpfer, B.Becker, M.Kampert, K-H.Kardan, B.Kedych, V.Kim, S.Koenig, I.Koenig, W.Kohls, M.Kolas, J.Kornakov, G.Kotte, R.Belounnas, A.Kres, I.Krueger, W.Kugler, A.Lalik, R.Lebedev, S.Linev, S.Linz, F.Lopes, L.Lorenz, M.Malige, A.Blanco, A.Markert, J.Matulewicz, T.Maurus, S.Metag, V.Michel, J.Molenda, A.Müntz, C.Nabroth, M.Naumann, L.Nowakowski, K.Blume, C.Opíchal, A.Orliński, J.Otto, J. -H.Parschau, M.Pauly, C.Pawlowska-Szymanska, D.Pechenov, V.Pechenova, OlgaPfeifer, D.Piasecki, K.Chlad, L.Pietraszko, J.Povar, T.Prościński, K.Prozorov, A.Przygoda, W.Pysz, K.Ramstein, B.Rathod, N.Ritman, J.Rost, A.Chudoba, P.Rustamov, A.Salabura, P.Saraiva, J.Scharmann, K.Schild, N.Schwab, E.Scozzi, F.Seck, F.Selyuzhenkov, I.Singh, U.Ciepał, I.Skorpil, L.Smyrski, J.Spies, S.Sreejith, A.Ströbele, H.Stroth, J.Sumara, K.Svoboda, O.Szala, M.Tlusty, P.Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeVNuclear Experiment (nucl-ex)High Energy Physics - Experiment (hep-ex)FOS: Physical sciencesWe 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.arXiv 9 pp. (2025). doi:10.48550/ARXIV.2512.12454info:eu-repo/semantics/preprintinfo:eu-repo/semantics/publishedVersionarXiv2025info:eu-repo/semantics/closedAccessDEhttps://repository.gsi.de/record/365286https://repository.gsi.de/search?p=id:%22GSI-2026-00377%22Researchersinfo:eu-repo/semantics/altIdentifier/doi/10.48550/ARXIV.2512.12454