We present three-particle mixed-harmonic correlations cos(mφa + nφb − (m + n)φc ) for harmonics
m, n = 1 − 3 for charged particles in
√
sNN = 200 GeV Au+Au collisions at RHIC. These measurements
provide information on the three-dimensional structure of the initial collision zone and are important for
constraining models of a subsequent low-viscosity quark–gluon plasma expansion phase. We investigate
correlations between the first, second and third harmonics predicted as a consequence of fluctuations in
the initial state. The dependence of the correlations on the pseudorapidity separation between particles
show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the
art hydrodynamic calculations with different initial states and temperature dependent viscosities. These
measurements provide important steps towards constraining the temperature dependent viscosity and
longitudinal structure of the initial state at RHIC.