Search for the Strange Dibaryons with Baryon Correlations in Isobar Collisions at STAR

TL;DR

The paper tackles the question of whether strange dibaryons, such as the H-dibaryon ($S=-2$) and the $N\Omega$ dibaryon ($S=-3$), can form in high-energy nuclear collisions. It employs two-particle correlation functions for $p$–$\Xi^{-}$ and $p$–$\Omega^{-}$ pairs in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}=200$ GeV, analyzed with the Lednicky–Lyuboshitz formalism to extract near-threshold scattering parameters $f_0$ and $d_0$, informed by HAL QCD potentials. The results reveal a weakly attractive $p$–$\Xi^{-}$ interaction and, notably, a pronounced suppression at low $k^{*}$ in $p$–$\Omega^{-}$ consistent with a shallow bound state with binding energy $E\approx 1.5$–$1.6$ MeV (spin-averaged and quintet-channel fits yield $f_0$ around $-4.3$ to $-4.9$ fm). These findings align with HAL QCD predictions and provide the first experimental indication of a strange dibaryon, with implications for hyperon–nucleon interactions and the QCD phase diagram.

Abstract

Dibaryons provide insight into the strong interaction beyond conventional hadrons. Strange dibaryons, containing strange quarks, are especially valuable for probing hyperon-nucleon (YN) and hyperon-hyperon (YY) interactions. We report measurements of $p$-$Ξ^-$ and $p$-$Ω^-$ correlation functions in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}} = 200$ GeV. The analysis, using the Lednicky-Lyuboshitz formalism, yields scattering parameters that offer key implications for the possible formation of strange dibaryon bound states, particularly $H$ ($S = -2$) and $NΩ$ ($S = -3$).

Figures (6)

• Figure 1: $p$$-$$\Xi^{-}$ correlation functions in 0–10%, 10–40%, and 40–80% centralities for Ru+Ru (top), Zr+Zr (middle), and Au+Au (bottom) at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV. Black bars and boxes indicate statistical and systematic uncertainties, respectively. Magenta lines show simultaneous fits using the Lednický-Lyuboshitz model (including Coulomb and strong interactions), blue dashed lines show pure Coulomb, and orange band represents predictions obtained by combining HAL QCD potential with particle phase-space distributions generated by UrQMD pxikamiyapxiSasaki.
• Figure 2: The spin-averaged $p$$-$$\Xi^{-}$ scattering length parameter ($f_0$) extracted from simultaneous fits in Isobar and Au+Au collisions using the Bayesian method. The red point represent the results from simultaneous fits. The black points indicate the results for the three individual systems. The green band shows the prediction from HAL QCD pxikamiyapxiSasaki.
• Figure 3: Correlation functions for $p$$-$$\Omega^{-}$ and $\bar{p}$$-$$\overline{\Omega}^{+}$ pairs measured in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}} = 200$ GeV. Open black symbols represent the data with statistical (bars) and systematic (boxes) uncertainties. The magenta lines show fits using the Lednický-Lyuboshitz model with the spin-averaged method, while gray dashed lines represent Coulomb-only contributions. Blue bands indicate HAL QCD predictions HALQCD:2014okwMorita:2019rph. The insets are showing a zoom into the region near unity.
• Figure 4: (a) The extracted $p$$-$$\Omega^{-}$ scattering parameters, scattering length ($f_0$) and effective range ($d_0$), are shown as probability contours from spin-averaged (red) and quintet (blue) methods. Solid points mark best fits and blue bands show 1–3$\sigma$ confidence levels from the quintet method. (b) The $p$$-$$\Omega^{-}$ binding energy (BE), calculated via the Bethe formula, is shown with experimental points from spin-averaged (red) and quintet (blue) fits. HAL QCD prediction and QDCSM calculation are indicated by yellow inverted triangle and diamond markers, respectively HALQCD:2018qyuYan:2024aap.
• Figure 5: Extracted final state interaction parameters: scattering length ($f_0$) and effective range ($d_0$) for $p$--$\Lambda$ (blue), $p$$-$$\Xi^{-}$ (black) and $p$$-$$\Omega^{-}$ (red) pairs.