The Hawking effect—the amplification of fluctuations at the horizon—has been detected in quantum fluids through real-space density correlations. However, real-space observables integrate over frequency, mixing distinct scattering channels into a single interference pattern and obscuring the spectral and entanglement structure of the emission. Here, we numerically compute momentum-space two-point correlations in a transcritical quantum fluid, using the truncated Wigner approximation applied to a realistic, driven-dissipative polariton system. We spectrally resolve the Hawking-partner channel as well as graybody factor channels and find that both carry comparable correlation strength, demonstrating that the well-known real-space “moustache” is an interference between these spectrally distinct contributions. The Hawking-partner channel is dominated by negative correlations, a direct signature of quantum-vacuum pair creation. All features reach amplitudes detectable in state-of-the-art experiments. Our results establish that the full three-mode output state must be considered for entanglement characterization, and they provide a general framework applicable to any quantum fluid.

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• Quantum fields in curved spacetime
• Polariton condensate