Baryonium states: where do they begin?

Abstract

An investigation of the mass levels of ground and excited qqq̅q̅ (baryonium) states is carried out within a Bethe-Salpeter framework for a four-body system with pairwise q-q̅ q-q interactions of the h.o. type. The identity of quarks, and separately, of antiquarks, in a qqq̅q̅ system gives rise to a well-defined set of selection rules governing the spin-isospinorbital structures of T- and M-baryonia. A relativistic mass formula, similar to those derived recently for qq̅ and qqq systems, including spin and momentum dependent effects, is now obtained for the qqq̅q̅ system. The values of the parameters employed for mass prediction for qqq̅q̅ states, viz., the non-strange quark mass (m_q = 0.28) and the reduced spring constant (ω˜ = 0.15), are the same as those used earlier for a successful description of non-strange qq̅ and qqq spectroscopy in a unified fashion. The main prediction on the mass locations is that the orbitally unexcited qqq̅q̅ states are all in the range 2.5-3.1 GeV, the lowest one (a scalar T-baryonium) being around 2.5 GeV. Possible experimental significance of this result is breifly discussed in the latest context of disappearance of the sharp features of most baryonium states.