Tcc in the diabatic diquark model: Effects of D∗D isospin

Tcc+ is an isoscalar 4-quark state with mass lying barely below the D∗+D0 threshold, and several times further below the D∗0D+ threshold. It allows both dimeson molecular and elementary diquark-antidiquark (cc)(ūd¯) substructures. The diabatic generalization of the adiabatic approximation within the Born-Oppenheimer formalism rigorously incorporates the mixing of such elementary eigenstates with states corresponding to two-particle thresholds. We examine the separate influence of the two D∗D isospin channels and find that the influence of D∗+D0 is larger than that of D∗0D+ but not overwhelmingly so, and that Tcc+ contains an O(10%) (cc)(ūd¯) component. We then explore the variation of these results if the isospin breaking between the dimeson thresholds is varied, and also the sensitivity of our results to variation of the mixing-potential parameters.