Comparison of hydrodynamic model of graphene with recent experiment on measuring the Casimir interaction

We obtain the reflection coefficients from a graphene sheet deposited on a material substrate under a condition that graphene is described by the hydrodynamic model. Using these coefficients, the gradient of the Casimir force in the configuration of recent experiment is calculated in the framework of the Lifshitz theory. It is shown that the hydrodynamic model is excluded by the measurement data at the 99% confidence level over a wide range of separations. From the fact that the same data are in a very good agreement with theoretical predictions of the Dirac model of graphene, the low-energy character of the Casimir interaction is confirmed.