Quark models of dibaryon resonances in nucleon-nucleon scattering

Abstract

We look for $\ensuremath{\Delta}\ensuremath{\Delta}$ and $N\ensuremath{\Delta}$ resonances by calculating $\mathit{NN}$ scattering phase shifts of two interacting baryon clusters of quarks with explicit coupling to these dibaryon channels. Two phenomenological nonrelativistic chiral quark models giving similar low-energy $\mathit{NN}$ properties are found to give significantly different dibaryon resonance structures. In the chiral quark model (ChQM), the dibaryon system does not resonate in the $\mathit{NNS}$ waves, in agreement with the experimental SP07 $\mathit{NN}$ partial-wave scattering amplitudes. In the quark delocalization and color screening model (QDCSM), the $S$-wave $\mathit{NN}$ resonances disappear when the nucleon size $b$ falls below 0.53 fm. Both quark models give an ${\mathit{IJ}}^{P}={03}^{+}\ensuremath{\Delta}\ensuremath{\Delta}$ resonance. At $b=0.52$ fm, the value favored by the baryon spectrum, the resonance mass is 2390 (2420) MeV for the ChQM with quadratic (linear) confinement, and 2360 MeV for the QDCSM. Accessible from the ${}^{3}{D}_{3}^{\mathit{NN}}$ channel, this resonance is a promising candidate for the known isoscalar ABC structure seen more clearly in the $\mathit{pn}\ensuremath{\rightarrow}d\ensuremath{\pi}\ensuremath{\pi}$ production cross section at 2410 MeV in the recent preliminary data reported by the CELSIUS-WASA Collaboration. In the isovector dibaryon sector, our quark models give a bound or almost bound ${}^{5}{S}_{2}^{\ensuremath{\Delta}\ensuremath{\Delta}}$ state that can give rise to a ${}^{1}{D}_{2}^{\mathit{NN}}$ resonance. None of the quark models used have bound $N\ensuremath{\Delta}P$ states that might generate odd-parity resonances.