Axialvector diqaurk Mass and quark-diquark potential in Sigma_c

The axialvector diquark is studied by using 2+1 flavor Lattice QCD. Being a two-quark object, diquark has a non-neutral color charge. Hence the two-point correlators of diquark fields do not have a particle pole due to the color confinement of QCD, and it is not straightforward to study the diquark mass by lattice QCD by using an exponential fit of a temporal two-point correlator. In order to avoid this difficulty, our strategy is to regard the diquark mass as a mass parameter of an effective quark-diquark model which is constructed by using an extended HAL QCD method based on equal-time quark-diquark Nambu-Bethe-Salpeter (NBS) wave functions. We attempt to calculate the axial-vector diquark mass and the quark-diquark potentials between a charm quark and an axial-vector diquark in the $\Sigma_c$ baryon. Lattice QCD Monte Carlo calculation is performed by using the 2+1 flavor QCD gauge configurations generated on $32^3\times 64$ lattice by PACS-CS Collaboration which corresponds to the pion mass of about 700 MeV. As a result, a quark-diquark central potential of Cornell-type and a short-ranged spin-dependent potential are obtained. However, from a quantitative point of view, the ground state convergence of the NBS wave functions are not sufficient so that we obtain a larger string tension and a smaller axial-vector diquark mass than we have expected phenomenologically.