Diffusion Monte Carlo calculations of fully-heavy multiquark bound states

Abstract

We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation describing fully heavy tetraquark systems. This approach allows us to reduce the uncertainty of the numerical calculation at the percent level, accounts for multiparticle correlations in the physical observables, and avoids the usual quark clustering assumed in other theoretical techniques applied to the same problem. The interaction between particles was modeled by the most general and accepted potential—i.e., a pairwise interaction including Coulomb, linear-confining and hyperfine spin-spin terms. This means that, in principle, our analysis should provide some rigorous statements about the mass location of the all-heavy tetraquark ground states, which is particularly timely due to the very recent observation made by the LHCb Collaboration of some enhancements in the invariant mass spectra of J=ψ pairs. Our main results are as follows: (i) The cc¯ c¯ c, cc¯ b¯ b (bb¯ c¯ c), and bb¯ b¯ b lowest-lying states are located well above their corresponding meson-meson thresholds. (ii) The JPC ¼ 0þþ cc¯c¯ c ground state with preferred quark-antiquark pair configurations is compatible with the enhancement(s) observed by the LHCb Collaboration. (iii) Our results for the cc¯ c¯ b and bb¯ c¯ b sectors seem to indicate that the 0þ and 1þ ground states are almost degenerate, with the 2þ located around 100 MeV above them. (iv) Smaller mass splittings for the cb¯ c¯ b system are predicted, with absolute mass values in reasonable agreement with other theoretical works. (v) The 1þþ cb¯ c¯ b tetraquark ground state lies at its lowest S-wave meson-meson threshold, and it is compatible with a molecular configuration.