Quenched and unquenched quark models can explain the bottomonium sector

An open question in hadronic phenomenology concerns the "unquenching" effects of higher Fock space components on the leading Fock space description of hadrons. In a paper by Eric Swanson (UPitt, co-PI), in collaboration with Muhammad Atif Sultan (Punjab U.), Wei Hao, and Lei Chang (Nankai U.), we address this by comparing the bottomonium spectrum as computed with the relativized Godfrey-Isgur quark model and an unquenched coupled channel model driven by the ${}^3P_0$ mechanism of hadronic decay. Our results show that both models can accurately describe the spectrum, indicating that the influence of coupled channel effects can be largely absorbed into the parameters of the quenched quark model. This conclusion is reinforced by a perturbative calculation that demonstrates the spin dependence of mass splittings due to mixing with the continuum recapitulates quenched quark model spin-dependent interactions. We also show that the softening of the quark-antiquark wave function due to continuum mixing improves the description of vector bottomonium decay constants. Together, these results illustrate and substantiate the surprising robustness of simple constituent quark model descriptions of hadrons. 

Papers: arXiv:2503.10178