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The lowest-lying glueballs are investigated in lattice QCD using $N_f=2$clover Wilson fermion on anisotropic lattices. We simulate at two different andrelatively heavy quark masses, corresponding to physical pion mass of$m_\pi\sim 938$ MeV and $650$ MeV. The quark mass dependence of the glueballmasses have not been investigated in the present study. Only the gluonicoperators built from Wilson loops are utilized in calculating the correspondingcorrelation functions. In the tensor channel, we obtain the ground state massto be 2.363(39) GeV and 2.384(67) GeV at $m_\pi\sim 938$ MeV and $650$ MeV,respectively. In the pseudoscalar channel, when using the gluonic operatorwhose continuum limit has the form of $\epsilon_{ijk}TrB_iD_jB_k$, we obtainthe ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pionmasses. These results are compatible with the corresponding results in thequenched approximation. In contrast, if we use the topological charge densityas field operators for the pseudoscalar, the masses of the lowest state aremuch lighter (around 1GeV) and compatible with the expected masses of theflavor singlet $q\bar{q}$ meson. This indicates that the operator$\epsilon_{ijk}TrB_iD_jB_k$ and the topological charge density couple ratherdifferently to the glueball states and $q\bar{q}$ mesons. The observation ofthe light flavor singlet pseudoscalar meson can be viewed as the manifestationof effects of dynamical quarks. In the scalar channel, the ground state massesextracted from the correlation functions of gluonic operators are determined tobe around 1.4-1.5 GeV, which is close to the ground state masses from thecorrelation functions of the quark bilinear operators. In all cases, the mixingbetween glueballs and conventional mesons remains to be further clarified inthe future.

Glueball spectrum from $N_f=2$ lattice QCD study on anisotropic lattices