Revisiting $K_1(1270)- K_1(1400)$ mixing in QCD sum rules

We investigate the $K_1(1270)-K_1(1400)$ mixing caused by the flavor $SU(3)$ symmetry breaking. The mixing angle is expressed by a $K_{1A}\to K_{1B}$ matrix element induced by the operators that breaks flavor $SU(3)$ symmetry. The QCD contribution to this matrix element is assumed to be dominated and calculated by QCD sum rules. A three-point correlation function is defined and handled both at the hadron and quark-gluon levels. The quark-gluon level calculation is based on operator product expansion up to dimension-5 condensates. A detailed numerical analysis is performed to determine the Borel parameters, and the obtained mixing angle is $\theta_{K_1}=22^{\circ}\pm 7^{\circ}$ or $\theta_{K_1}=68^{\circ}\pm 7^{\circ}$.