arXiv · 2512.12454
Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\mathrm{\sqrt{s_{NN}}}$ = 2.55 GeV
Abstract
We present the first observation of $\mathrm{^{3}_\Lambda H}$ and $\mathrm{^{4}_\Lambda H}$ 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 $\Lambda$ hyperons. The resulting rapidity distributions, dN/dy, exhibit a bell shape centered at mid-rapidity. The yield of $\mathrm{^{4}_\Lambda H}$ is equal to or exceeds that of $\mathrm{^{3}_\Lambda H}$, 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 $\mathrm{^{3}_\Lambda H}$, a lifetime of $\mathrm{\tau_{^{3}_\Lambda H}}$ = $(239 \pm 23{\mathrm{(stat)}} \pm 18{\mathrm{(sys)}})\,\mathrm{ps}$, is extracted, consistent on the 1$\sigma$ level with that of the free $\Lambda$. In contrast, the $\mathrm{^{4}_\Lambda H}$ lifetime of $\mathrm{\tau_{^{4}_\Lambda H}}$ = $(209 \pm 7{\mathrm{(stat)}} \pm 10{\mathrm{(sys)}})\,\mathrm{ps}$, shows a 4.5 $\sigma$ deviation from the free $\Lambda$ 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://arxiv.org/abs/2512.12454
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