Gravitational waves (GWs) emanated by stellar-mass compact binary coalescences (CBCs), and lensed by galaxy- or cluster-scale lenses, will produce two or more copies of the GW signal. In the geometric-optics limit, these signals will have similar phase evolution but differing amplitudes. Such lensing signatures are expected to be detected by the end of the LIGO-Virgo-KAGRA Collaboration’s fifth observing run. In this work, we propose a novel ${\chi }_{\mathrm{lens}}^2$ statistic to segregate pairs of detected GW events as lensed or unlensed, using templates typically used in GW searches. The statistic is an application of the generalized ${\chi }^2$ discriminator, tailored to probe the similarity (or lack thereof) between the phase evolutions of two CBC signals. We assess the performance of ${\chi }_{\mathrm{lens}}^2$ on an in-part astrophysically motivated dataset of lensed and unlensed CBCs detectable in the fourth observing run, assuming a single LIGO-like detector at design sensitivity. Our results show that ${\chi }_{\mathrm{lens}}^2$ correctly identifies lensed events with efficiencies comparable to existing Bayesian and machine learning methods, while being orders of magnitude faster to evaluate than Bayesian methods. Moreover, the statistical properties of ${\chi }_{\mathrm{lens}}^2$ in stationary Gaussian noise are fully understood, in contrast to machine learning methods. ${\chi }_{\mathrm{lens}}^2$ can, therefore, be used to rapidly and accurately weed out the vast majority of unlensed candidate pairs and identify lensed pairs.

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• Gravitational wave sources
• Gravitational waves