Jarlskog invariant ($J$)

The Jarlskog invariant is a rephasing-invariant measure of CP violation in a three-generation quark mixing matrix. It is the common magnitude of imaginary quartic products such as $\mathrm{Im}(V_{ij}{V}_{k\ell }{V}_{i\ell }^{\ast }{V}_{kj}^{\ast })$ for distinct rows and columns.