Glueball spectrum from N _f = 2 lattice QCD study on anisotropic lattices

Abstract

The lowest-lying glueballs are investigated in lattice QCD using N f = 2 clover Wilson fermion on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion mass of mπ ∼ 938 MeV and 650 MeV. The quark mass dependence of the glueball masses have not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363(39) GeV and 2.384(67) GeV at mπ ∼ 938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ijk T rBiDjB k , we obtain the ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter (around 1GeV) and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ijk T rBiDjB k and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.

Study of the pseudoscalar glueball in J/ψ radiative decays

“…The authors get the result m η = 1019(119) MeV at the physical pion mass consistent with the physical η mass. Similar lattice studies have also been carried out in the N f = 2 case [8,28]. In Ref.…”

“…In Ref. [8], the authors get the mass of the isoscalar pseudoscalar η 2 to be m η2 = 890(38) MeV at m π = 650 MeV. In Ref.…”

Central exclusive diffractive production of K+K−K+K− via the intermediate ϕϕ state

“…The nature of these resonances is not understood at present and a tensor glueball has still not been clearly identified. According to lattice-QCD simulations, the lightest tensor glueball has a mass between 2.2 and 2.4 GeV; see, e.g., [44][45][46][47][48][49][50]. The f 2 (2300) and f 2 (2340) states are good candidates to be tensor glueballs.…”

Holographic QCD predictions for production and decay of pseudoscalar glueballs

“…Most lattice results have been obtained in the quenched approximation 1 , i.e. without dynamical quarks, but recent unquenched lattice calculations [18][19][20] have found no evidence for significant unquenching effects, which however should be expected if the pseudoscalar glueball were to mix strongly with radially excited η( ) mesons. Moreover, Ref.…”

“…Moreover, Ref. [20] recently reported that correlation functions of pseudoscalar gluonic operators built from Wilson loops did not show any trace of the flavor singlet pseudoscalar meson states which can be found in the topological charge density correlator. In fact, on the experimental side it is still a controversial issue whether as many as three states η(1295), η(1405), and η(1475) (and thus indication of the involvement of the pseudoscalar glueball in this mass region) really exist.…”