Speaker
Description
We report preliminary results from $\Lambda\Lambda$ invariant-mass spectroscopy in the ${}^{12}\mathrm{C}(K^{-}, K^{+})$ reaction to search for the H-Dibaryon near the $\Lambda\Lambda$ and $\Xi^{-}p$ thresholds at J-PARC. The experiment employs a $1.8~\mathrm{GeV}/c$ $K^{-}$ beam incident on a diamond target and a large-acceptance hyperon spectrometer centered on a time-projection chamber (HypTPC). This setup provides sensitivity over a broad mass region, ranging from weakly bound states below the $\Lambda\Lambda$ threshold to possible structures above the $\Xi^{-}p$ threshold.
A total of approximately $300{,}000$ ${}^{12}\mathrm{C}(K^{-}, K^{+})X$ reaction events were collected, yielding several thousand $\Lambda\Lambda$ events---about two orders of magnitude more than in previous experiments. In the $(K^{-}, K^{+})$ reaction on a nuclear target, $\Lambda\Lambda$ production proceeds through interactions on di-protons inside the nucleus. The production mechanisms include intermediate $\Xi^{-}$ formation as well as meson-induced two-step processes, such as $K^{-}p \rightarrow \Xi^{-}K^{+}$ followed by $\Xi^{-}p \rightarrow \Lambda\Lambda$, and $K^{-}p \rightarrow \pi^{0}\Lambda$ followed by $\pi^{0}p \rightarrow \Lambda K^{+}$.
In our earlier work, we measured the differential cross section for the ${}^{12}\mathrm{C}(K^{-}, K^{+}\Lambda\Lambda)$ reaction and the contributions from the $\Xi^{-}p \rightarrow \Lambda\Lambda$ conversion and meson-induced two-step processes[1] Based on these results, we have carried out invariant-mass spectroscopy of the $\Lambda\Lambda$ system to investigate the possible existence of the H-Dibaryon near threshold and to gain further insight into the $\Lambda\Lambda$--$\Xi N$ interaction. In this presentation, we will show preliminary results of the H-Dibaryon search and discuss its nature.
[1] W.S. Jung et al., Prog. Theor. Exp. Phys. 2025, ptaf064.