Encounters With Dibaryons: Recent Discoveries And Ongoing Research.pdf

Have They Finally Become True?

This paper reviews the long history of dibaryon searches, highlighting a recent breakthrough. After decades of false alarms and theoretical predictions, experimental evidence for a bound dibaryon state has been found.

Background:

- Early Days (1950s - 1970s): Initial searches focused on resonances in NN scattering and pion production. Theoretical models based on quarks emerged, predicting various dibaryon states, leading to a "dibaryon rush" era of experimental claims. However, none were confirmed.
- Dysfunction of Early Searches: Poor data quality, inclusive measurements, and statistical fluctuations contributed to the failure of these searches. K.K. Seth (1988) famously called for honest hard work in exclusive experiments.
- Resonance in 1D2 Partial Wave: A candidate resonance in the 1D2 partial wave of NN scattering was proposed in the 1950s and later analyzed in the 1960s, 80s, and 90s. Its interpretation as a genuine s-channel resonance remains debated.

Recent Breakthrough:

- WASA-at-COSY Results (2010s): The WASA collaboration observed a dominant resonance in the double-pionic fusion reaction pn → dπ0π0 at √s = 2.37 GeV with Γ ≈ 70 MeV, decaying predominantly via an intermediate ΔΔ system.
- Key Evidence: New data on polarized np scattering confirm this resonance as a pole in coupled 3D3 −3 G3 partial waves, providing strong evidence for the existence of dibaryons.
- Theoretical Interpretations: Relativistic three-body calculations and quark models successfully predict characteristics of this resonance, including its narrow width due to hidden-color components. This resonance is dubbed the "inevitable dibaryon" d∗.

Conclusion:

After decades of searching, experimental evidence for a bound dibaryon state has finally been established. The WASA-at-COSY results mark a significant milestone in our understanding of hadronic physics and open new avenues for exploring exotic quark states.