Spin structure of spin-1 charmonium states near $T_c$

Abstract

We investigate the spin structure of the $1^{--}$ and $1^{++}$ charmonium states near the critical temperature using QCD sum rules. To this end, we compute the contribution of the dimension-4 twist-2 gluon operator to the two-point function of heavy vector and axial vector currents in a rotating frame. As temperature increases, the quark spin contribution slightly increases, while the quark orbital angular momentum decreases by a comparable amount. The gluon contribution remains nearly unchanged. These thermal changes cancel each other, ensuring that the total spin is preserved even at finite temperature.