Nuclear Momentum Transfer in Invisible-Dark-Boson Searches at the Electron–Ion Collider

We quantify the benefit of nuclear momentum-transfer information in invisible-dark-boson searches at the Electron–Ion Collider. We compare optimized rectangular cuts, an estimated likelihood selection, and boosted decision trees (BDTs) for coherent scalar and vector production in electron–gold collisions at 18 GeV by 100 GeV per nucleon. Each method uses electron-only inputs or adds t, the positive magnitude of the squared nuclear four-momentum transfer. The generator-level comparison uses common weighted samples, preselection, and a significance objective, with ten independent runs at 11 masses for each boson type. At 10 GeV, adding t improves significance by approximately 31–39% across the three methods. With t included in all methods, BDT and likelihood selections give approximately 3% further improvement over cuts and have similar performance. At this mass, the benefit of t persists under illustrative 10% and 20% relative smearing and the tested photon-loss variations.