Search for the $H$-dibaryon resonance in ${}^{12}\mathrm{C}$ $(K^{-},K^{+}\Lambda \Lambda X)$

The $H$-dibaryon resonance was sought by a $\Lambda \Lambda$ invariant mass spectrum that was obtained by the ${}^{12}\mathrm{C}$ $(K^{-},K^{+}\Lambda \Lambda X)$ reactions. We observed a bump near the $\Lambda \Lambda$ threshold, as reported by the previous experiment (KEK E224), with better statistics. Data were compared with results of a cascade model calculation including $\Lambda \Lambda$ final state interactions consistent with the newly measured binding energy of ${}_{\Lambda \Lambda }^6\text{He}$. No significant enhancements above levels of the model predictions were observed. The resulting upper limit for the production cross section of the $H$ with a mass range between the $\Lambda \Lambda$ and $\Xi N$ threshold is found to be 2.1 ± 0.6 (stat.) ± 0.1 (syst.) μb/sr at a 90% confidence level.

Figure 1

Top view of KEK E522 experimental setup (a) and schematic drawing of the scintillating fiber active target (b).

Figure 2

Typical image of the $\Lambda \Lambda$ in the scintillating fiber active target.

Figure 3

Reconstructed mass distribution of two-Λ candidates.

Figure 4

Proper time of two-Λ data. Efficiency was corrected.

Figure 5

$\Lambda \Lambda$ invariant mass spectrum compared with theoretical predictions and with experimentally deduced backgrounds. Binning was done corresponding to the different resolutions, 5 and 15 MeV/$c^2$. Error bars are statistical only.