  One flavor mass reweighting can be used in lattice QCD computations to fine
tune the quark masses to their physical values. We present a new method that
utilizes an unbiased stochastic estimation of the one flavor determinant. The
stochastic estimation is based on the integral representation of the
determinant of a complex matrix, which we prove. In contrast to other methods
it can also be applied in situations where the determinant has a complex phase.
The stochastic error is controlled by determinant factorizations based on mass
interpolation and Schur decomposition. As an example of an application we
demonstrate how the method can be used to tune the up-down quark mass
difference.
