Hidden-beauty charged tetraquarks and heavy quark spin conservation

Abstract

Assuming the dominance of the spin-spin interaction in a diquark, we point out that the mass difference in the beauty sector M(Zb′)±-M(Zb)± scales with quark masses as expected in QCD, with respect to the corresponding mass difference M(Zc′)±-M(Zc)±. Notably, we show that the decays γ (10890)→ γ (nS)π+π- and γ(10890)→(hb(1P),hb(2P))π+π- are compatible with heavy quark spin conservation if the contributions of Zb,Zb′ intermediate states are taken into account, γ (10890) being either a γ (5S) or the beauty analog of Yc(4260). Belle results on these decays support the quark spin wave function of the Z states as tetraquarks. We also consider the role of light quark spin nonconservaton in Zb,Zb′ decays into BB∗ and B∗B∗. Indications of possible signatures of the still missing Xb resonance are proposed.