Lattice study of the masses of singlet0++mesons

Abstract

We compute the masses of the flavour singlet 0 ++ mesons using (n f = 2) unquenched lattice QCD with the Iwasaki and Wilson gauge actions. Both fermionic and glueball interpolating operators are used to create the states. The mass of the lightest 0 ++ meson is suppressed relative to the mass of the 0 ++ glueball in quenched QCD at an equivalent lattice spacing. We discuss two possible physical reasons for this.

Near-maximal mixing of scalar gluonium and quark mesons: A Gaussian sum-rule analysis

“…Indeed, the existence of such strong mixing implies that qualitative features that would distinguish pure gluonic and qq states would be obscured for strongly-mixed states and the experimental signal of gluonium would thus be elusive. In summary, our results provide strong QCD evidence to support the scenario where the mixing of qq and gluonium is manifested in the scalar hadronic spectrum as a lighter state on the order of 1 GeV and a heavier state on the order of 1.5 GeV [4,6,8,9,10,11,12,15]. In particular, our conclusion that there exists a strong mixing between gluonium and qq states is similar to the results from a variety of approaches [6,8,9,10] and our result for the heavier state's preference for gluonic channels provides QCD support for the findings of a large gluonic component of the f 0 (1500) [2,3].…”

“…Lattice QCD calculations lead to a scalar gluonium state of approximately 1.6 GeV with quenched quarks [7]. However, with dynamical quarks the mixing with qq states appears to be very strong, driving the mass of the lightest flavour-singlet meson down toward 1 GeV with tentative identification of an excited state on the order of 1.5 GeV [8]. The vast literature on mixing of gluonia in QCD sum-rules is reviewed in detail in [9].…”

Scalar mesons in a finite volume

“…Indeed, recent years have seen considerable activity, concerning the calculation of the spectrum of the scalar mesons on the lattice (see, e.g., [25][26][27][28][29][30][31][32][33][34][35][36][37][38]). However, alone the calculations of the excited spectrum do not answer the question.…”

Hadronic decays from the lattice

“…This has not yet been achieved, for a summary of the current state of lattice studies see ref. [18].…”

“…This hadronic transition has been studied using quenched [16] and dynamical lattices [17] A full lattice study is needed which includes glueball, qq and ππ channels but the disconnected diagram for f 0 → ππ is very noisy in practice -as shown in ref. [18]. To reduce the contribution from disconnected diagrams, one can study flavour non-singlet scalar mesons.…”